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Perovskite solar cells: surface, interface and materials aspects

The Symposium C is devoted to the presentation of original contributions on fundamental research at the surface and interface, and materials science engineering of the perovskite solar cells. Both theoretical and experimental studies which focus on the preparation or understanding of materials for perovskite solar cells are relevant.


The performance of perovskite solar cells, critically depends on the interfaces between the individual layers. For instance, efficient generation of charges, extraction, and transport with minimum recombination through interlayer interfaces is crucial to attain high-efficiency solar cell devices. During the overlayer formation many unexpected reactions may occur that in effect may change the expected energy bands positions and thus the charge transport properties across the layers. The interfacial reactions often lead to the degradation of the perovskite solar cells and hence to the performance and stability of these devices. Besides that, the perovskite film itself can be grown as an intrinsic, n-type or/and p-type material depending on the used substrate. Most of the preparation methods like spin-coating, co-evaporation, vapor-assisted deposition, etc. developed to prepare perovskite generate films with polycrystalline grains. The adjacent grains may assume different crystal orientations and/or have different chemical compositions, which impacts charge excitation and dynamics and thereby the overall solar cell performance. The unbalanced charge accumulation or depletion between grain boundaries and grain interiors can cause band bending, which affects the separation of photoexcited electron−hole pairs and charge carrier transport across the grain interfaces formed between grains. Therefore, it is crucial to investigate the correlation between local electronic properties and local morphologies. 

The aim of this Symposium is to gather together all researchers involved in the investigation of the (new) perovskite materials for photovoltaic applications and to provide a discussion forum for them.   Papers related to all aspects of the fundamental properties of the perovskite materials and devices, i.e. new materials for stable and efficient perovskite solar cells, laboratory- and synchrotron-based characterization of the surface and interfaces in the perovskite solar cell stacks, perovskite-inspired materials, application of hybrid perovskites in LED and photoelectrochemical water splitting devices, non-PV applications of hybrid perovskite films, new deposition techniques for industrialization of perovskite solar cells, to name a few, are invited.

Hot topics to be covered by the symposium:

  • Ex-situ, in-situ and in-operando studies of the perovskite materials and devices
  • New materials and interfaces for stable and efficient photovoltaics
  • Low-temperature processes for perovskite devices fabrication 
  • Perovskites in tandem with other materials
  • Perovskites for non-photovoltaics (LED, water splitting) applications
  • Perovskite-inspired materials
  • Atomic layer deposition (ALD) for perovskite-based devices
  • Engineering transparent conducting oxides (TCOs) for perovskite-based devices 
  • Development of flexible perovskite-based photovoltaics
  • Modeling of perovskite materials and solar cells  
  • 2D and 3D perovskites

Confirmed invited speakers:

  • Steve Albrecht, Tandem solar cells, Helmholtz-Zentrum Berlin (Germany)
  • Juan-Pablo Correa Baena, Promises and challenges in perovskite solar cells, Massachusetts Institute of Technology (USA)
  • Mariadriana Creatore, ALD for perovskite solar cells, Eindhoven University of Technology (The Netherlands)
  • Dipankar Das Sarma, Electronic properties of hybrid perovskites, Indian Institute of Science (India)
  • Caterina Ducati, Characterising degradation of perovskite solar cells through in-situ and operando Electron Microscopy, University of Cambridge (UK)
  • Germa Garcia-Belmonte, Device and interfacial properties of the perovskite solar cell, Institute of Advanced Materials (Spain)
  • Selina Olthof, Substrate-dependent electronic structure and film formation of MAPbI3 perovskites, University of Cologne (Germany)
  • Nam-Gyu Park, Methodologies toward highly efficient perovskite solar cells, Sungkyunkwan University (South Korea)
  • Daniel Prochowicz, Mechanochemical Approach to Inorganic-Organic Hybrid Materials for Perovskite Solar Cells,Polish Academy of Sciences in Warsaw (Poland)
  • Byungha Shin, In-situ Observation of Oxygen Migration in a n-i-p Type Organometal Halide Perovskite Solar Cell under Electrical Biasing, Korea Advanced Institute of Science and Technology (South Korea)
  • Zhiping Wang, Efficient ambient-air-stable solar cells with 2D–3D heterostructured butylammonium-caesium-formamidinium lead halide perovskites, University of Oxford (UK)
  • Konrad Wojciechowski, Printable perovskite solar cells, Saule Technologies (Poland)

Scientific committee members:

  • Antonio Abate (Germany)
  • Thomas Bein (Germany)
  • David Cahen (Israel)
  • Konrad Domanski (Switzerland)
  • Karsten Henkel (Germany)
  • Lukas Kegelmann (Germany)
  • Olga Malinkiewicz (Poland)
  • Barry Rand (USA)
  • Philip Schulz (France)
  • Shahzada Ahmad (Spain)
  • Trilok Singh (India)
  • Henry Snaith (UK)


Participants of the Symposium C will have a unique possibility to publish their results in a Themed Issue on “Electronic Properties and Characterisation of Perovskites" at the Journal of Materials Chemistry C (Impact factor = 5.256). The issue is currently being planned for publication in Journal of Materials Chemistry C Volume 7 (2019) with a deadline for article submissions in late 2018.

More information will be published soon.

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09:00 Welcome and Opening Remarks    
Fundamentals of Perovskite Solar Cells : Małgorzata Kot
Authors : Dr. Sylvain Nicolay
Affiliations : Section Head Coatings PV-center Rue Jaquet-Droz 1, CH-2002 Neuchâtel, Switzerland

Resume : The aim of CHEOPS is to develop very low-cost but highly performing photovoltaic (PV) devices based on the emerging perovskite (PK) technology. For single junction devices, CHEOPS aim at scaling up the lab results to single junction modules manufactured in a preproduction environment while maintaining high efficiencies (>14% stable for aperture area in modules >15x15cm2). In parallel, CHEOPS develop materials and processes to achieve very high efficiency (>29% on 2x2cm2 cells) at low cost (target <0.4¤/Wp) using a tandem configuration with a crystalline silicon heterojunction cell. CHEOPS also performs a sustainability assessment from a life-cycle perspective to anticipate potential risks for the technology (including business, technological, environmental, social & political risks). Most recent project results will be presented including single junction module with 1.35% steady state efficiency on 45 cm2 aperture area and 25.2% certified efficiency for a perovskite/Silicon tandem device using fully textured Si wafers.

Authors : D. D. Sarma
Affiliations : Solid State & Structural Chemistry Unit, Indian Institute of science, Bengaluru 560012, India

Resume : Along with the intense effort to further improve the efficiency and other technological aspects, there is a considerable effort in understanding intrinsic properties of hybrid perovskite halides. Curiously enough, there does not appear to be any universally accepted understanding of even the most basic properties of these materials. For example, an intensely debated issue concerns the ability of permanent dipoles on organic moieties to give rise to polar fields, either in the normal state (as in any ferroelectric material) or in the photo-excited state, contributing to its spectacular photovoltaic properties. Even estimates of the excitonic binding energy in these materials have proven to be controversial with various estimates differing by more than an order of magnitude. I shall discuss our own efforts with various pure and solid solution samples of APbX_3 to understand physical properties of several of these hybrid materials. We use different techniques that are sensitive to the polar nature of any given material, probing time-scales from the static down to a few hundred femto-seconds, both without and in presence of photo-excitation to address several outstanding issues. This work is a result of collaborations with B Bhattacharyya, M Bokdam, C De, C Franchini, S Ghara, TN Guru Row, A Hossain, BP Kore, G Kresse, A Kumar, J Lahnsteiner, P Mahale, A Mohanty, S Mukherjee, S Pal, A Pandey, MS Pavan, S Picozzi, T Sander, Sharada G, A Stroppa, A Sundaresan, and D Swain. Relevant references: 1. M Bokdam et al., Sci. Rep. 2016, 6, 28618 2. J Lahnsteiner et al., Phys. Rev. B 2016, 94, 214114 3. Sharada G et al., J. Phys. Chem. Lett. 2016, 7, 2412 4. Sharada G et al., J. Phys. Chem. Lett. 2017, 8, 4113 5. Sharada G et al., J. Phys. Chem. C (ASAP, 2018)

Authors : Jingrui Li, Jari Järvi, Mariana Rossi, Patrick Rinke
Affiliations : Department of Applied Physics, Aalto University, Finland (JL, JJ, PR); Fritz Haber Institute of the Max Planck Society, Theory Department, Berlin, Germany (MR)

Resume : Hybrid perovskite photovoltaics has received rapidly growing interest from the emerging solar-cell community due to its record increase in power-conversion efficiency. To further advance this technology, we need to understand the hybrid perovskite (HP) materials on the atomic scale, on which the light-to-energy conversion and transport processes occur. Currently, this atomic scale is riddled with controversies. For the detachment of methylammonium (MA) cations from the PbI3 cage in the most common HP material MAPbI3, very low as well as high (∼100 meV) activation energies (Ea) have been reported. Quasi-elastic neutron scattering measurements (QENS) for the orthorhombic phase found Ea=48 meV, which was attributed to the axial rotation of the whole MA cation [1]. To shed light on this controversy, we performed density-functional theory (DFT) calculations (PBE0 functional + van der Waals corrections + inclusion of nuclear quantum effects) for several rotational MA processes [2]. For the torsional rotation, we obtain Ea=42 meV in good agreement with the QENS result. We therefore ascribe this barrier to the rotation of CH3 against the NH3 unit, which remains bound to the PbI3 cage. For the full axial rotation, which breaks three hydrogen bonds, we obtain a much higher barrier (∼120 meV) and therefore conclude that this process is not likely to occur. [1] Chen et al., Phys. Chem. Chem. Phys. 17 31278 (2015). [2] Li et al., J. Phys. Chem. Lett. submitted.

Authors : G. A. Nemnes [1,2], Cristina Besleaga [3], A. G. Tomulescu [3], Alexandra Palici [3], L. Pintilie [3], A. Manolescu [4], Ioana Pintilie [3]
Affiliations : [1] Horia Hulubei National Institute for Physics and Nuclear Engineering, 077126 Magurele-Ilfov, Romania; [2] University of Bucharest, Faculty of Physics, Materials and Devices for Electronics and Optoelectronics Research Center, 077125 Magurele-Ilfov, Romania; [3] National Institute of Materials Physics, Magurele 077125, Ilfov, Romania; [4] School of Science and Engineering, Reykjavik University, Menntavegur 1, IS-101 Reykjavik, Iceland;

Resume : The dynamic effects observed in the J-V measurements represent one important hallmark in the behavior of the perovskite solar cells. Proper measurement protocols (MPs) should be employed for the experimental data reproducibility, in particular for a reliable evaluation of the power conversion efficiency (PCE), as well as for a meaningful characterization of the type and magnitude of the hysteresis. We discuss several MPs by comparing the experimental J-V characteristics with simulated ones using the dynamic electrical model (DEM). Under certain re-poling conditions and bias scan rates a hysteresis-less behavior with relatively high PCEs may be observed, although the J-V characteristics are far away from the stationary case. Furthermore, forward-reverse and reverse-forward bias scans show qualitatively different behaviors regarding the type of the hysteresis, normal and inverted, depending on the bias pre-poling. We emphasize here that correlated forward-reverse or reverse-forward bias scans are essential for a correct assessment of the dynamic hysteresis. In this context, we define a hysteresis index which consistently assigns the hysteresis type and magnitude. Our DEM simulations, supported by experimental data, provide further guidance for an efficient and accurate determination of the stationary J-V characteristics, showing that the type and magnitude of the dynamic hysteresis may be affected by unintentional pre-conditioning in typical experiments. [arXiv:1803.00285]

10:30 Coffee Break    
Efficiency of Perovskite Solar Cells : Chittaranjan Das
Authors : Nam-Gyu Park
Affiliations : Sungkyunkwan University

Resume : Since the first report on the solid-state perovskite solar cell (PSC) with power conversion efficiency (PCE) of 9.7% and 500 h-stability in 2012 by our group, researches on PSCs increase exponentially. As a result, PCE approaching 23% was reported, which is higher than conventional inorganic thin film solar cells, and publications reached more than 9,000 as of May 2018. It is believed that PSC is promising next-generation photovoltaics due to superb performance and very low cost. In this talk, the history of perovskite photovoltaics will be presented along with their scientific progress and perspective. For reproducible and high quality perovskite film, Lewis acid-base adduct method was developed. Grain-boundary healing method was developed via non-stoichiometric approach. Grain boundary healing process yields PCE as high as 20.4%. Method for reduction in hysteresis and improving moisture stability was developed by interfacial engineering using 2-dimensioanl perovskite. A universal method to eliminate hysteresis even in normal mesoscopic structure was discovered. Large-area coating technology was developed to commercialize high efficiency PSCs via perovskite single crystals (or powder) based viscous liquid approach. A unique bifacial technique was developed to produce high PCE (>20%) MAPbI3, FAPbI3 and other compositions at mild condition. Halide perovskite is now extend to X-ray imaging, LED and resistive memory areas, which will be also discussed in this talk.

Authors : Lukas Kegelmann, Christian M. Wolff, José Antonio Márquez Prieto, Philipp Tockhorn, Lars Korte, Thomas Unold, Dieter Neher, Bernd Rech, Steve Albrecht
Affiliations : Helmholtz-Zentrum Berlin, Berlin, 12489, Germany; University of Potsdam, Institute of Physics and Astronomy, Potsdam, 14476, Germany; Helmholtz-Zentrum Berlin, Berlin, 12489, Germany; Helmholtz-Zentrum Berlin, Berlin, 12489, Germany; Helmholtz-Zentrum Berlin, Berlin, 12489, Germany; Helmholtz-Zentrum Berlin, Berlin, 12489, Germany; University of Potsdam, Institute of Physics and Astronomy, Potsdam, 14476, Germany; Helmholtz-Zentrum Berlin, Berlin, 12489, Germany; Helmholtz-Zentrum Berlin, Berlin, 12489, Germany;

Resume : Perovskite solar cells have seen a tremendous increase in efficiencies to above 22% within few years. By now, the device parameter with the largest potential for further improvements is the open circuit voltage (Voc), which is mainly governed recombination losses at the interfaces. Here, a water-free poly(3,4-ethylenedioxythiophene) (PEDOT) layer doped with sulfonated copolymers is utilized as hole selective contact (HSC) on top of perovskite absorbers. Transient photoluminescence (PL) and steady-state PL quantum yield measurements reveal longer charge carrier lifetimes and larger quasi-fermi level splitting for perovskite films with PEDOT atop. PEDOT thin films therefore seem to suppress charge carrier recombination at the perovskite surface. By blending undoped Spiro-OMeTAD into the PEDOT dispersion, the surface energetics of the resulting films are shifted to larger ionisation energies as measured by photoelectron spectroscopy and the charge extraction is enhanced as implied by transient PL and impoved fill factors in complete devices. As a result, perovskite solar cells with mixtures of PEDOT and Spiro-OMeTAD as HSC achieve high Voc values up to 1.19 V and stabilized efficiencies over 16%. This exceeds both the Voc and PCE of reference devices with doped Spiro-OMeTAD or pure PEDOT as HSC in this study.

Authors : Chun-Guey Wu Chien-Hung Chiang
Affiliations : National Central University, Taiwan

Resume : Planar heterojunction organic-perovskite hybrid solar cell is one of the most promising photovoltaic architecture to achieve high efficiency with low temperature process. Several processes to synthesis high quality perovskite film at room temperature were disclosed. Combining with high mobility hole transporting and electron transporting layers, the planar heterojunction perovskite-PC71BM solar cell achieves the power conversion efficiency above 20% and a reasonable stability. The champion cell shows no current hysteresis both in voltage scan directions and scan rates. The growth mechanism of the high quality perovskite film can be manipulated using several strategies under low temperature. Be able to control the nucleation/ growth of the perovskite crystals makes the fabrication of high-efficiency perovskite solar cell rather reproducible.

Authors : Pietro Caprioglio⁑†, Fengshuo Zu ǂ‡, José A. Márquez Prietoǂ, Christian M. Wolff ⁑, Martin Stolterfoht ⁑, Saul Daniel Cruz Lemus°, Norbert Koch ǂ‡, Thomas Unoldǂ, Markus Antonietti°, Bernd Rech §, Steve Albrecht †§ and Dieter Neher ⁑
Affiliations : ⁑ University of Potsdam Institut für Physik und Astronomie Physik weicher Materie, Potsdam, Germany; ‡ Humboldt-Universität, Institut für Physik, Berlin , Germany; § Helmholtz-Zentrum Berlin, Institute for Silicon Photovoltaics, Berlin , Germany; † Helmholtz-Zentrum Berlin, Young Investigator Group Perovskite Tandem Solar Cells, Berlin , Germany; ǂHelmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany; °Max Planck Institute of Colloids and Interfaces, Berlin, Germany;

Resume : Metal halide perovskite solar cells are now effectively competing with their inorganic counterparts in terms of power conversion efficiencies. However, state of the art perovskite solar cells still suffer from limited fill factor (FF) and open circuit voltage (Voc), which has been related to non-geminate losses mostly happening at the surface of the perovskite absorber. Therefore, it is of imperative importance to address these types of losses and try to minimize them. One way to suppress this type of charge carrier recombination is to appropriately modify the perovskite surface in order to slow down surface recombination and, accordingly, improve its interface with the charge transporting layers as it was shown that this is the predominant loss channel. Here, we present the improvement of solar cell devices in a p-i-n solar cell architecture utilizing PTAA and C60 as hole and electron transporting layers by two different surface modifications. We combine this with an in-depth understanding of the physical processes involved in both actual devices and the bare material itself by the means of a series of detailed combined analyses. First, we show the enhancement of the Voc by adding Strontium (Sr) to a quadruple cation perovskite Rb5(Cs5(MA0.17FA0.83)95)95Pb(I0.83 Br0.17)3 in which the Sr mostly accumulates at the perovskite surface. The resulting material displays significantly enhanced photoluminescence (PL) lifetime and absolute PL yield, indicating strong reduction of non-radiative surface recombination. Consequently, in the actual devices, it has been found that the Voc drastically increases from 1.11 V to 1.18 V, along with an improvement of the electroluminescence efficiency of more than one order of magnitude, with resulting power conversion efficiency (PCE) over 20%. Upon detailed investigation of morphology (electron microscopy and secondary ion mass spectroscopy) and energetics (photoelectron spectroscopy), we found that Sr segregates at the surface where it induces a more n-type surface with a consequent strong band-banding. We propose that such a surface modification creates a back-surface field able to repel holes from the surface, thus reducing the probability of a trapped electron recombining with a hole in the valence band. Additionally, this screening effect brings a substantial improvement of the perovskite-C60 interface, compensating for the lack of selectivity of the latter. Second, we developed a treatment of the triple cation Cs5(MA0.17FA0.83)95)95Pb(I0.83 Br0.17)3 perovskite surface with a Polyimidazole derivative polyionic liquid. Here, this surface modification enables a beneficial improvement of the FF as well as an enhancement of the Voc. The resulting solar cell devices show outstanding FF values of up to 82.5% and extraordinarily PCE of over 21%. In conclusion, we propose that through exclusively addressing the surfaces it is possible to efficiently suppress the non-radiative recombination of charges and consequently reduce the energy losses. Additionally, our results can be representative of a more general methodology for device modification, and therefore potentially applicable to other compositions and cell architecture.

Authors : M. Elshobaki,1 M. Elnaggar,2 A. Mumyatov,3 S. Luchkin,1 K.J. Stevenson1 and P.A. Troshin1,3
Affiliations : 1Skolkovo Institute of Science and Technology, Nobel st. 3, Moscow, Russia, 2Department of Kinetics and Catalysis, Institute of Physics and Technology, Dolgoprudny, Moskovskaya oblast', Moscow, Russia, 3Institute for Problems of Chemical Physics of RAS, Chernogolovka, Moscow region, Russia

Resume : The power conversion efficiency of organic-inorganic perovskite solar cells has soared from 3.8% in 2009 to the current record exceeding 22%. Long-term stability of perovskite solar cells not only depends on the photoactive layer, but also on the proper selection of interfacial layers. Efficient and stable interfaces offer minimized energy-level offsets and good isolation of the perovskite layer preventing its decomposition. Here we report new fullerene-derivatives as more promising alternatives to the commonly used PCBM material, which improve the efficiency and stability of the devices in inverted configuration. Our findings show that new fullerenes: (1) provide good coverage atop of the MAPbI3 layer as confirmed by conductive AFM imaging; (2) yield efficient charge quenching confirmed by PL measurements; and (3) enhance the power conversion efficiency of PEDOT-based p-i-n devices reaching 15%. Most importantly, two of the new fullerene derivatives provided excellent isolation of the perovskite active layer resulting in largely improved thermal and ambient (60% RH in air) stability of the solar cells.

12:30 Lunch Break    
Stability of Perovskite Solar Cells : Steve Albrecht
Authors : Zhiping Wang
Affiliations : Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU, United Kingdom.

Resume : Over the last few years metal halide perovskite based solar cells have undergone a meteoric rise in cell efficiency to > 22%. Increasing importance of improving solar cell operation is reliant upon understanding and controlling thin-film crystallisation and controlling the nature of the heterojunctions between the perovskite with the p and n-type charge extraction layers. In addition, understanding and enhancing long term stability of the materials and devices is a key driver. In this talk, I will highlight the key factors which are important for reaching the maximum efficiencies and long-term operational stability, and also areas where we know require further improvement. I will specifically highlight recent advances in understanding the enhancement of long term stability through appropriate choice and adaptation of charge selective interlayers, interfacial doping and trap passivation[1?4]. I will also highlight the importance of tailoring the perovskite composition; especially introduce the creation of stable 2D-3D heterostructures within a perovskite film, for device stability improvement[5]. References: [1] Z. Wang, D. P. McMeekin, N. Sakai, S. van Reenen, K. Wojciechowski, J. B. Patel, M. B. Johnston, H. J. Snaith, Adv. Mater. 2017, 29, 1604186. [2] Y. Hou, X. Du, S. Scheiner, D. P. McMeekin, Z. Wang, N. Li, M. S. Killian, H. Chen, M. Richter, I. Levchuk, N. Schrenker, E. Spiecker, T. Stubhan, N. A. Luechinger, A. Hirsch, P. Schmuki, H. P. Steinrück, R. H. Fink, M. Halik, H. J. Snaith, C. J. Brabec, Science (80-. ). 2017, 358, 1192. [3] M. Kot, C. Das, Z. Wang, K. Henkel, Z. Rouissi, K. Wojciechowski, H. J. Snaith, D. Schmeisser, ChemSusChem 2016, 9, 3401. [4] M. Daskeviciene, S. Paek, Z. Wang, T. Malinauskas, G. Jokubauskaite, K. Rakstys, K. T. Cho, A. Magomedov, V. Jankauskas, S. Ahmad, H. J. Snaith, V. Getautis, M. K. Nazeeruddin, Nano Energy 2017, 32, 551. [5] Z. Wang, Q. Lin, F. P. Chmiel, N. Sakai, L. M. Herz, H. J. Snaith, Nat. Energy 2017, 2, 17135.

Authors : Jonas A. Schwenzer, Lucija Rakocevic, Tobias Abzieher, Diana Rueda-Delgado, Robert Gehlhaar, Bryce S. Richards, Uli Lemmer, Ulrich W. Paetzold
Affiliations : Jonas A. Schwenzer; Tobias Abzieher; Diana Rueda-Delgado; Bryce S. Richards; Uli Lemmer; Ulrich W. Paetzold: LTI, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany Lucija Rakocevic; Robert Gehlhaar: imec, Leuven, 3001, Belgium Lucija Rakocevic: ESAT, KUL, Leuven, 3000, Belgium Bryce S. Richards; Uli Lemmer; Ulrich W. Paetzold: IMT, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, 76344, Germany

Resume : With power conversion efficiencies (PCEs) exceeding 22%, perovskite solar cells (PSCs) are considered to be a promising alternative to established photovoltaic technologies. The main challenge of the technology is the limited stability. In this study, we reveal the importance of the right choice of materials when considering outdoor applications of PSCs. We present a novel degradation mechanism in PSCs that is not apparent at constant temperatures but has a heavy impact on the performance when the temperature is varied. This degradation can lead to reductions in photocurrent and thus efficiency as high as 80% within less than three hours in the TiO2/perovskite/Spiro-MeOTAD architecture, that is one of the most commonly used architectures. Identifying the underlying physical process of this degradation mechanism and proposing possibilities to overcome it is in the focus of this contribution. By exchanging the electron and hole transport layer as well as the perovskite absorber, we systematically investigate the role of the interfaces on this novel degradation process. We show that one of several routes to avoid the temperature variation induced degradation is to use C60 instead of TiO2 as electron transport layer. Combining all of these results, we demonstrate a PSC architecture that is stable for several hours under realistic outdoor temperature variations with a PCE of up to 19.5%.

Authors : Christopher J. Bartel, Christopher Sutton, Bryan R. Goldsmith, Runhai Ouyang, Charles B. Musgrave, Luca M. Ghiringhelli, Matthias Scheffler
Affiliations : University of Colorado, Chemical and Biological Engineering; Fritz Haber Institute, Theory; University of Michigan, Chemical Engineering; Fritz Haber Institute, Theory; University of Colorado, Chemical and Biological Engineering; Fritz Haber Institute, Theory; Fritz Haber Institute, Theory

Resume : Predicting the stability of the perovskite structure remains a longstanding challenge for the discovery of new functional materials for photovoltaics, fuel cells, and many other applications. Using a novel data analytics approach based on SISSO (sure independence screening and sparsifying operator), an accurate, physically interpretable, and one-dimensional tolerance factor, τ, is developed that correctly classifies 92% of compounds as perovskite or nonperovskite for an experimental dataset containing 576 ABX3 materials (X = O, F, Cl, Br, I). In comparison, the widely used Goldschmidt tolerance factor, t, achieves a maximum accuracy of only 74% for the same set of materials. The probability of forming stable perovskites is mapped continuously as a function of the sizes of the A, B, and X ions revealing physical insights into how these relative sizes yield stable and unstable perovskite structures. Additionally, the new tolerance factor is shown to compare well with DFT-calculated decomposition enthalpies of single and double perovskite oxides and chalcogenides. τ is applied to identify more than a thousand inorganic (Cs2BB’Cl6) and hybrid organic-inorganic (MA2BB’Br6) double perovskites that are predicted to be stable.

Authors : Philippe Holzhey, Michael Saliba
Affiliations : Philippe, (1) Fachbereich Physik, Freie Universität Berlin, (2) Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne; Michael Saliba, (1) Adolphe-Merkel Institute, Fribourg

Resume : The stability of perovskite solar cells has been considered poor compared to other solar cells. One reason for this is thought to be the volatile organic methylammonium (MA) cation. At the same time, small amounts of MA are used for practically all highest performing solar cells with efficiencies beyond 21%. These compositions have also shown some of the best reported stabilities indicating that MA might not be as unstable as previously assumed. This raises the question whether excluding MA for the sake of stability has been concluded prematurely. Here, we use weakest link devices, i.e. MAPbI3, to study the stability under light and different temperatures.

Authors : Haibing Xie1, Zaiwei Wang2, Kubicki Dominik Józef3, Agarwalla Anand2, Hui-Seon Kim2, Prochowicz Daniel3, Alba Mingorance1, Jose Carlos Pereyra1, Amador Perez-Tomas1, Shaik Mohammed Zakeeruddin3, Michael Grätzel3, Anders Hagfeldt2*, Monica Lira-Cantu1*
Affiliations : 1. Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and the Barcelona Institute of Science and Technology (BIST). Building ICN2, Campus UAB E-08193, Bellaterra, Barcelona, Spain. 2. Laboratory of Photomolecular Science (LSPM), Institute of Chemical Sciences and Engineering, School of Basic Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. 3. Laboratory for Photonics and Interfaces (LPI), Institute of Chemical Sciences and Engineering, School of Basic Sciences, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.

Resume : We are moving towards a sustainable society powered by renewal energy where solar photovoltaics is one of the most important players. In the past few years, emerging photovoltaic (PV) technologies have observed an exponential increase in power conversion efficiencies (PCE) with halide perovskite solar cells above 22 %, tandem photovoltaics reaching 26 % or dye sensitized solar cells for indoor lighting at the impressive 28.9 % PCE mark. Oxides in solar cells can be found as the main solar absorber responsible for photon-to-electron conversion, as interfacial layers for the transport of electron or holes, as part of the conductive metal electrodes (including transparent electrodes) and also as part of photon management. Among the many advantages is the ease of fabrication, low cost and enhanced stability that provide to the solar cell. Moreover, new-generation of oxides (e.g. doped or undoped, binary, ternary, ferroelectric, etc.) are slowly breaking ground providing competitive power conversion efficiencies, enhanced transport properties or improved UV-light stability, among others. We report our most recent studies on the application of classic oxides (binary, doped, nanostructured) and complex oxide compounds (ternary, ferroelectric, etc.) as transport layers in Halide Perovskite Solar Cells. We will show the effect of metal oxides and their surface functionalization on solar cell efficiency and long-term stability. [1] A. Hagfeldt, M. Lira-Cantu, Recent concepts and future opportunities for oxides in solar cells, Applied Surface Science, (2018) Submitted. [2] A. Perez-Tomas, A. Mingorance, Y. Reyna, M. Lira-Cantu, Metal Oxides in Photovoltaics: All-Oxide, Ferroic, and Perovskite Solar Cells, in: M. Lira-Cantu (Ed.) The Future of Semiconductor Oxides in Next Generation Solar Cells, Elsevier, 2017, pp. 566. [3] M. Lira-Cantú, Perovskite solar cells: Stability lies at interfaces, Nature Energy, 2 (2017) nenergy2017115. [4] M. Lira-Cantu, The future of semiconductor oxides in next generation solar cells, 1st ed., Elsevier, 2017. [5] Y. Reyna, M. Salado, S. Kazim, A. Pérez-Tomas, S. Ahmad, M. Lira-Cantu, Performance and Stability of Mixed FAPbI3(0.85)MAPbBr3(0.15) Halide Perovskite Solar Cells Under Outdoor Conditions and the Effect of Low Light Irradiation., Nano Energy, 30 (2016) 570–579.

15:30 Coffee Break    
Devices : Derya Baran
Authors : Konrad Wojciechowski
Affiliations : Saule Technologies

Resume : Metal halide perovskites constitute a very attractive class of materials for optoelectronic applications, such as solar cells, light emitting diodes, lasers and photodetectors. Most notably, solid-state photovoltaic devices based on these materials have reached power conversion efficiencies (PCEs) of 22% after just five years of academic research. Perovskite solar cells have a great commercial potential, but there still remain few challenges, which need to be resolved to prove the viability of the technology. Some of the well-known issues include material stability. Furthermore, cost-effective, reliable fabrication process capable of delivering highly efficient, large-area perovskite modules is yet to be demonstrated. This talk will outline the industrial challenges of perovskite solar cells including legislative hurdles as well as the potential impact on the solar industry. Moreover, we will present fully scalable ink-jet printing process of the perovskite PV stack and fabrication of perovskite printable mini-modules of areas up to A4 size, complemented with a robust encapsulation methodology.

Authors : Steve Albrecht1, Eike Köhnen1, Marko Jost1, Anna B. Morales-Vilches2, Amran Al-Ashouri1, Klaus Jäger3, Luana Mazzarella2, Bernd Stannowski2, Lars Korte4, Bernd Rech4, and Rutger Schlatmann2
Affiliations : 1 Young Investigator Group Perovskite Tandem solar cell, 2 PVcomB, 3Young Investigator Group Nano-SIPPE, 4 Institute for Silicon Photovoltaics, Helmholtz-Center Berlin, 12489 Berlin, Germany

Resume : Combining inorganic?organic perovskites and crystalline silicon solar cells into monolithic tandem solar cells has recently attracted increased attention due to the high efficiency potential of this cell architecture. Promising results with certified efficiencies as high as 23.6% were realized and published in early 2017 [1]. To further increase the tandem device performance to a level well above the best silicon single junctions at 26.7%, optical and electrical optimizations as well as a detailed device understanding of this advanced tandem architecture need to be developed. Here we present our recent results on monolithic perovskite/silicon-heterojunction tandem solar cells that reach a certified conversion efficiency of 25.0%. This remarkable achievement was enabled by several experimental improvements as compared to our previous reports [2]. Guided by our optical simulations [3,4], we selected the front contact layer stack with less parasitic absorption utilizing an (?inverted?) perovskite top cell in the p-i-n contact design and combined it with an adapted rear-emitter silicon heterojunction cell into a tandem device. In addition, optical and electrical optimization of the n-type front contact stack together with improving the optoelectronic quality of the perovskite bulk and the interfaces to the adjacent charge selective layers were necessary to achieve the high efficiency. With the help of a detailed loss analysis, experimental guidelines for further improvements will be shown. The analysis shows that realistic efficiencies above 30% are within reach for monolithic tandem cells when the perovskite band-gap is enlarged and optimized light trapping/light management techniques are successfully implemented. [1] Bush, K. A.; Palmstrom, A. F.; Yu, Z. al. Nature Energy 2017, 2, 17009. [2] Albrecht, S.; Saliba, M.; Correa Baena, J. P. et al. Energy Environ. Sci. 2016, 9, 81. [3] Jäger, K.; Korte, L.; Rech, B. et al. Optics Express 2017, 25, A473. [4] Mazzarella, L.; Werth, M.; Jäger, K. et al. Optics Express 2018, 26, A487.

Authors : Stefano Pisoni, Thierry Moser, Romain Carron, Thomas Feurer, Shiro Nishiwaki, Ayodhya N. Tiwari, Stephan Buecheler
Affiliations : Laboratory for Thin Films and Photovoltaics, Empa – Swiss Federal Laboratories for Material Science and Technology, Ueberlandstrasse 129, Duebendorf, Switzerland

Resume : For all thin film based tandem solar cells, perovskite solar cell (PSC) represents an ideal candidate for wide band gap top cell in combination with low band gap Cu(In,Ga)Se2 (CIGS) bottom cell. The possibility to develop highly efficient perovskite and CIGS solar cells on flexible substrates lays the foundations to lightweight flexible tandem devices by high-throughput roll-to-roll manufacturing. Here, we report a multi-stage perovskite deposition approach by combining vacuum- and solution-based techniques, where the morphology of vacuum deposited PbI2 is appropriately tailored to enhance organic cation intercalation. The preferential growth of the inorganic layer is the result of minimization of combined surface and interface energy. Depending on the specific substrate surface nature, compact or nanostructured PbI2 morphologies can be obtained. With this process, we have achieved steady-state efficiencies of 15.8% and 14.0% for opaque and NIR-transparent PSCs, respectively, on a flexible front sheet which is used for flexible CIGS module encapsulation. Further, flexible perovskite/CIGS tandem with 19.6% efficiency were measured in four-terminal configuration. Eventually, through optical loss analysis, we define potential pathways for more efficient flexible NIR-transparent PSCs. Our work represents a step forward towards new concepts for flexible thin film tandem devices, and provides insights into growth of layers and interfaces for high efficiency flexible solar cells.

Authors : H. Kim, H. W. Jang
Affiliations : Department of Materials science and Engineering, Seoul National University, Seoul, Korea

Resume : Resistive switching memory devices based on 2-dimensional halide perovskites The halide perovskite is the crystal structure formed with the general formula ABX3, where A cation is larger than B cation, and X represents the halide (Cl, Br, or I) anion. And the ABX3 halide perovskite shows a 3-dimensional (3D) structure corresponding to a corner-sharing octahedral network. The halide perovskite shows unique property and fast ion migration, which plays a major role in resistive switching behavior and causes current–voltage (I–V) hysteresis. The halide perovskite materials have received great attention as potential alternatives to conventional materials and begun to be applied to resistive switching memory devices. However, in the resistive switching process which has repeatable formation and rupture of filaments in an insulating layer, conducting filaments in the 3D halide perovskite structure are difficult to control the strength, shape, and uniformity, because charged defects randomly migrate in 3D structure. To overcome these issues, 2D layered halide perovskites can be applied to the memory devices instead of 3D halide perovskites. The 2D layered perovskite structures are formed by inserting large molecule at A sites in the 3D frames, which means that the 3D structures are broken, then become layered structures. Herein, we successfully apply CsPbI3 with phenylethyl ammonium (PEA) for 2D layered-perovskite in resistive switching memory devices, and the device structure is Ag/polymethylmethacrylate (PMMA)/(PEA)2Csn−1PbnI3n+1/Pt/Ti/SiO2/Si stack. The uniform perovskite film is synthesized on the substrate using low temperature all-solution process and the 2D layered-perovskites exhibit bipolar resistive switching behavior. Previously, the characteristics of CsPbI3 (3D perovskite) switching memory devices exhibit the ON/OFF ratio of 109 and a root mean square (RMS) roughness of 9.883 nm. But interestingly, the switching memory devices based on (PEA)2Csn−1PbnI3n+1 (2D perovskite) shows ON/OFF ratio of 109 with ultralow operating voltage (<0.20 V) and a RMS roughness of 2.634 nm. This research will contribute to the improvement of switching behavior of memory devices and the better understanding on the resistive switching mechanisms based on the 2D layered halide perovskites.

Authors : Ji Su Han, Quyet Van Le, Soo Young Kim, Ho Won Jang
Affiliations : Department of Materials Science and Engineering, Seoul National University; School of Chemical Engineering and Materials Science, Chung-Ang University; School of Chemical Engineering and Materials Science, Chung-Ang University; Department of Materials Science and Engineering, Seoul National University

Resume : Organometal and all-inorganic halide perovskites (HPs), ABX3, where A is the organic (CH3NH3) or inorganic (Cs, Rb) cation, B is a metal cation (Pb, Sn), and X is a halide anion (Cl, Br, or I), are regarded as promising functional materials due to their exotic properties such as tunable bandgap, fast ion migration, facile majority carrier control, and super-flexibility as well as optoelectronic characteristics. With their unique property of current-voltage hysteresis caused by fast ion migration, they have begun to be actively applied to resistive switching (RS) memory devices beyond optoelectronics. Resistive switching random-access memory (ReRAM), which can be applied to memristors, neuromorphic technology, and logic-in-memory application, is considered to be a promising nonvolatile memory device due to its low power consumption, fast switching speed, and high integration density. Many ReRAM devices with HPs have been reported, however, the general HPs have an environmental problems by including toxic lead element. Cesium lead iodide, well known all-inorganic HP, contains lead element which is harmful to the environment. To be environmentally friendly, the lead element has to be replaced with harmless elements such as Sn, Bi. Despite the seriousness of environmental problems caused by lead element, there are still few reports about lead-free HP in RS memory device. Herein, we successfully apply a lead-free and all-inorganic cesium tin iodide (CsSnI3) perovskite in RS memory device. The RS memory device has Ag or Au/polymethylmethacrylate (PMMA)/CsSnI3/Pt/Ti/SiO2/Si structure. A pinhole-free and uniform perovskite film with a thickness of only 300 nm is synthesized on a platinum coated silicon substrate using low temperature all-solution process. Interestingly, the RS memory devices based on CsSnI3 perovskites exhibit bipolar RS behavior in both Ag and Au electrodes devices, respectively, which shows different switching mechanisms. The devices with Ag electrode exhibit filamentary RS behavior with ultralow operating voltage (<0.15 V) and on/off ratio of 103. In contrast, the devices with Au electrode show interface-type RS behavior with gradual resistance change. This study will contribute to the understanding of the RS mechanism based on HPs and suggests the possibility of the lead-free and all-inorganic perovskites for eco-friendly green memory.

Authors : Bronisław Psiuk
Affiliations : Pracownia Badań Strukturalnych, Termicznych i Termomechanicznych

Resume : Development of solar energy, is presented as one of the most important challenges posed ceramics in the twenty-first century. Realization of this requirement is associated with the searching of materials absorbing electromagnetic waves in the field of ultraviolet and visible light. One of the potential practical applications, using sunlight is photodegradation of organic impurities, in this phenol compounds in aqueous solutions. The most common compounds of the present heterogeneous catalytic systems are TiO 2 based materials. However, in order to reduce its energy gap (3.2eV) and activation also visible light for the mentioned processes the modification of this compound are performed. Another photocatalytic compouds, in this perovskite structure materials, are also studied. The work shows light absorption abilities of KNbO3 and SrTiO3 doped with V and Fe. The pure and doped samples were investigated especially with using UV-VIS spectrometry and additionaly by XRD, SEM and XPS methods. Photocatalytic properties have been tested in practice by examining the degradation of phenol in aqueous solutions. Both dopants caused improving of the absorption as compared to the undoped samples. The results showed also that the ability to absorb light in a wide wavelength range is not a sufficient condition to improvement of photocatalytic activities in practice.

Authors : Di Girolamo Diego, Piccinni Marco, Matteocci Fabio, Marrani Andrea, Di Carlo Aldo, Dini Danilo
Affiliations : Dept. of Chemistry, University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome,Italy ; Dept. of Chemistry, University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome,Italy ; Centre for Hybrid and Organic Solar Energy (CHOSE), Dept. of Electronic Engineering, University of Rome “Tor Vergata”, Via del Politecnico 1, 00133 Rome, Italy ; Dept. of Chemistry, University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome,Italy ; Centre for Hybrid and Organic Solar Energy (CHOSE), Dept. of Electronic Engineering, University of Rome “Tor Vergata”, Via del Politecnico 1, 00133 Rome, Italy , Department of Semiconductor Electronics and Device Physics, National University of Science and Technology,Moscow 119049, Russia ; Dept. of Chemistry, University of Rome “La Sapienza”, P.le A. Moro 5, 00185 Rome,Italy

Resume : Diffused exciting around lead halide perovskite photovoltaics is largely justified by skyrocketing increase in power conversion efficiency up to certified 22.7%. The race for record efficiency is far from the end, but research community nowadays is well aware that more important criticality need to be addressed. Unstability and scale-up losses of perovskite PV technology are fundamental limitation toward feasibility of real-world application. Selective contacts quality is a sine qua non and metal oxides, mainly TiO2, SnO2 and NiO, guarantee state of the art efficiency and stability. Processing of metal oxides thin film is at the heart of technology advancement with high interest application including catalysis, energy and electronics. Electrodeposition is one of the most powerful and intriguing deposition technique for metal oxides, due to reproducibility, processing from water, low cost, scalability and the high purity of deposit due to highly selective driving force for film nucleation and growth. We report anodic electrodeposition of NiO on TCO substrates and their implementation as hole selective contact in p-i-n PSC. Detailed investigation through nucleation-growth modelling of electrodeposition mechanism shed light on mass-transport limited process overlapping with oxygen evolution. The effect of electroplating parameters like the concentration and nature of support electrolyte, temperature and applied potential is thoroughly investigated. Deposition efficiency increases at higher temperature while suppor rt electrolyte suppress the deposition process due to nickel cation complexation in solution. Devices based on CH3NH3PbI3 processed in air employing electrodeposited NiO within the architecture ITO|NiO|PSK|PCBM|BCP|Ag deliver a stabilized efficiency up to 16%

Authors : Yinglong Jiang, Huanpo Ning, and Jian Yu*
Affiliations : Institute of Functional Materials and Department of Physics, Donghua University, Shanghai 201620, China *e-mail:

Resume : Ferroelectric materials take advantage of spontaneous electric polarization separating photo-excited carriers and above-bandgap output voltage. Compared with organic-inorganic hybrid perovskites, ferroelectric oxide perovskites are much stable in a wide range of mechanical, chemical and thermal conditions and be able to fabricate using low-cost methods. The bottlenecks for ferroelectric photovoltaic applications are their poor visible optical absorption and low electrical conductivity owing to wide bandgap. In this work, using B-site chemistry, bandgap of BiFeO3-based oxide perovskites has been judiciously engineered in the range of 1.20-2.06 eV, that make ferroelectric semiconductors feasible for wide light absorption and high energy conversion photovoltaic solar cell applications. In particular, La and Mn co-substituted BiFeO3 solid solution exhibits a narrow direct bandgap of 1.22 eV, that allows photon absorptions of ~80% sunlight spectrum. The electronic subshell configuration, reduce mass of unit cell, and tolerant factor/octahedral factor related to ionic size are attempted as descriptors to classify and data-mine the relationship between composition and bandgap property of BiFeO3-based oxide perovskites. This essay provides an efficient approach to make ferroelectric semiconductor photovoltaic solar cells for human sustainable and clean energy resource with power conversion efficiency possible beyond the Shockley-Queisser limit for conventional p-n junction solar cell.

Authors : Hock Beng Lee, Mi-Kyung Jeon, Jae-Wook Kang
Affiliations : Department of Flexible and Printable Electronics, Chonbuk National University, Jeonju, Korea.

Resume : Tailoring the organic cations composition has often been considered as the most effective approach to dictate the morphology and crystal structure of inorganic-organic halide based perovskite film. In this work, we demonstrate the fabrication of (FAPbI3)1−x(MAPbBr3)x perovskite solar cells (PSCs) with various composition ratios of x, (x = 0, 0.10, 0.125, 0.15 and 0.20) employing spin-coating method. The as-fabricated PSCs exhibit device architecture as follows: glass/indium tin oxide (ITO)/tin oxide(SnO2)/composite perovskite/Spiro-oMeTAD/Ag. Specifically, the composite perovskite film acts as an active light-harvesting layer, whereas SnO2 and Spiro-oMeTAD function as electron and hole transporting layer, respectively. The device performance of the PSC are evaluated with respect to the structural and optical properties of the perovskite film at different x composition. It was found that the addition of MAPbBr3 into FAPbI3 stabilized the perovskite phase, leading to more uniform and dense morphology. The incorporation of MAPbBr3 into FAPbI3 stabilized the perovskite phase and helped to enhance the power conversion efficiency (PCE) of PSCs. The optimal PSC device (at x = 0.15) exhibits the lowest series resistance and highest fill factor, resulting in a PCE of 17.06% with negligible hysteresis. In summary, this study offers insights on how the incorporation of MAPbBr3 altered the properties of the perovskite films and the photovoltaic performance of PSCs.

Authors : Ali Asgher Syed,1 Chung-Yan Poon,2 Hung Wing Li,2 Furong Zhu,1
Affiliations : 1- Department of Physics, Institute of Advance Materials, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong, China 2- Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong

Resume : Hole extraction layer (HEL) of the inverted planar perovskite solar cells (PSCs) plays a dominant role in determining the device performance. High short circuit current density, open circuit voltage and efficient charge collection with suppressed charge recombination can be achieved through controlled growth of the perovskite layer. In this work, the effect of sodium citrate modified poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT:PSS) HEL on improved perovskite growth and hence the performance of the PSCs was investigated. Power conversion efficiency (PCE) of >11.30% was achieved for PSCs made with a sodium citrate modified PEDOT:PSS HTL, which is >20% higher than that of a structurally identical control device (9.16 %). Incident-photon to current efficiency, light intensity-dependent J−V characteristics, scanning electron microscope (SEM) and X-ray diffraction (XRD) measurements were carried out to analyzed the performance enhancement of the PSCs. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements reveal that sodium citrate solution modification partially removes surface PSS content of PEDOT:PSS HTL. A significant increase in the ratio of PEDOT to PSS of about 0.197 was observed for the sodium citrate modified PEDOT:PSS, as compared to that of the pristine PEDOT:PSS layer (0.108). The increase in the ratio of PEDOT to PSS agrees with the observation of increase in the conductivity of sodium citrate modified PEDOT:PSS layer. We propose that the sodium citrate modified PEDOT:PSS HTL benefits the efficient operation of PSCs in two ways: (1) it assists the crystal growth to increase in the perovskite domain size, and (2) it favors the charge collection in the PSCs.

Authors : Barkha Tyagi, Hock Beng Lee, Jae-Wook Kang*
Affiliations : Graduate School of Flexible and Printable Electronics, Chonbuk National University, Jeon-ju 54896, Republic of Korea

Resume : In recent years, perovskite solar cells (PSCs) have attained state-of-the-art efficiency comparable to that of silicon solar cells. To further enhance the power conversion efficiency (PCE) and air stability of PSCs, it is imperative to optimize the device architecture, surface and interfacial morphology and composition of the active perovskite layer. Herein, we demonstrate the use of methylammonium bromide (MABr) as a passivation layer on top of MAPbI₃ film surface to effectively suppress charge recombination and simultaneously improve charge collection. The MAPbI₃ PSCs were prepared via one-step anti-solvent technique, in which tin oxide (SnO₂) and spiro-OMeTAD were used as electron (ETL) and hole transporting layer (HTL), respectively. Our findings show that the presence of MABr passivation layer has remarkably reduced the excessive PbI₂ phase, grain boundaries and surface defects of MAPbI₃ film. This facilitated the charge transfer in the device, resulting in > 10% increment in the PCE of the device (13.5%). In overall, this work manifests the defect-passivation and charge facilitator roles of interfacial passivation layer on the rear surface of perovskite film.

Authors : Marko Jost 1, Nopporn Rujisamphan 2, Thidarat Supasai 3, Steve Albrecht 1, Thomas Dittrich 4
Affiliations : 1 Helmholtz Center Berlin for Materials and Energy GmbH, Young Investigator Group Perovskite Tandem Solar Cells, Kekuléstr. 5, D-12489 Berlin, Germany 2 Nanoscience and Nanotechnology Graduate Program, Faculty of Science, King Mongkut’s University of Technology Thonburi, 10140, Bangkok, Thailand 3 Department of Materials Science, Faculty of Science, Kasetsart University, 10900, Bangkok, Thailand 4 Helmholtz Center Berlin for Materials and Energy GmbH, Institute of Si-Photovoltaics, Kekuléstr. 5, D-12489 Berlin, Germany

Resume : Planar p-i-n type (“inverted”) perovskite solar cells based on the mixed perovskite “triple cation” absorber (Cs0.05((CH3NH3)0.17(HC(NH2)2)0.83)0.95Pb(I0.83Br0.17)3 with an initial efficiency of more than 17% were cycled in a temperature range between room temperature and 180°C. Modulated photovoltage spectra were measured during and after each heating cycle of 40 min duration and correlated with current-voltage characteristics, which were measured at room temperature. Surprisingly, a decrease of the energy parameter of the exponential defect states near the band-gap was observed with increasing temperature up to 80°C. The photovoltage signals related to deep defect states increased strongly between 80 and 100°C and decreased between 100 and 120°C, in correlation with a local minimum of the parameters of the solar cell at 100°C. However, strong degradation of the efficiency of the solar cells set on at temperatures above 150°C. This can be related to formation of defects in the perovskite and/or instability of the electron-selective contact layer.

Authors : Yueli Liu, Rui Zhang, Qiao Chen, Rui Zhang, Keqiang Chen, Wen Chen
Affiliations : State Key Laboratory of Silicate Materials for Architectures, School of Materials Science and Engineering, Wuhan University of Technology

Resume : Wurtzite structure Cu2ZnSnS4 (CZTS) quantum dots (QDs) are successfully synthesized by the hot-injection method, and UV-vis spectra are introduced to measure optical properties of the CZTS QDs for choosing the suitable QDs as the hole-transporting materials (HTM) in the perovskite solar cells (PSCs). The solar cells based on 6.7 nm CZTS QDs with the band gap of 1.81 eV reach the power conversion efficiency (PCE) of 9.5%. The high PCE value is related to the improvement of the Jsc, resulting in the increasement of the external quantum efficiency (EQE) at 680 nm. The devices based on CZTS QDs also show a good stability of PCE value after several days, which may provide a simple and low-cost way for fabricating PSCs.

Authors : Celline Awino1, Katrin Hirselandt 2, Lukas Kegelmann 3, Eva Unger 2, Steve Albrecht 3, Thomas Dittrich1
Affiliations : 1 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institut für Silizium-Photovoltaik, Kekuléstr. 5, D-12489 Berlin, Germany 2 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Young Investigator Group Hybrid Materials Formation and Scaling, Kekuléstr. 5, D-12489 Berlin, Germany 3 Helmholtz Center Berlin for Materials and Energy GmbH, Young Investigator Group Perovskite Tandem Solar Cells, Kekuléstr. 5, D-12489 Berlin, Germany

Resume : Modulated surface photovoltage (SPV) spectroscopy is a powerful tool for ex-situ and quasi in-situ characterization of electronic properties related to the band gap (Eg), tail states (Et), direction of charge separation and diffusion length (L). Furthermore, SPV analysis does not require the preparation of contacts and can be performed after different stages of layer preparation, light soaking etc. Eg, Et and L depend on crystallization, defect formation, solvents, substrates, temperature, additives as well as aging and light soaking. Application of modulated SPV spectroscopy is demonstrated on the examples of the dependence of Eg and Et on the stoichiometry in CH3NH3Pb(I1-XBrX)3 films, on temperature in Mo / CH3NH3PbI3 / PMMA, on different kinds of interfaces and degradation. Furthermore, the degradation of L under light soaking is demonstrated.

Authors : Dirk Döhler*, Pascal Büttner*, Julien Bachmann*°
Affiliations : * Department of Chemistry and Pharmacy, Friedrich-Alexander University of Erlangen-Nürnberg, Egerlandstraße 3a, D – 91058 Erlangen, Germany; ° Saint-Petersburg State University, Institute of Chemistry, Universitetskii pr. 26, 198504 St. Petersburg, Russia

Resume : Organic-inorganic hybrid perovskite solar cells evolved to one of the hot topics in the photovoltaic community due to facile processing and high efficiencies. A compact and continuous electron transporting material (ETM) is often used for recombination inhibition. This can be performed by spin coating, spray pyrolysis or atomic layer deposition (ALD). Using ALD, the thickness of these compact layers can be controlled precisely. Due to the self-limiting layer-by-layer process even complex morphologies can be coated with a well-defined homogeneous layer. We present perovskite solar cells with planar geometry using ALD as a crucial method in the manufacturing process of the ETM. ALD allows for a systematic tuning of the layer thickness and chemical composition. Also, two or more different layers can be combined to facilitate the charge extraction. The ALD film is analyzed by spectroscopic ellipsometry. The cell morphology and composition is characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. The cell performance is measured by cyclic voltammetry and external quantum efficiency measurements. The use of ALD surface treatments paves the way towards three-dimensional perovskite solar cell architectures based on nanoporous 'anodic' aluminum oxide templates.

Authors : Pascal Büttner*, Dirk Döhler*, Julien Bachmann*°
Affiliations : * Department of Chemistry and Pharmacy, Friedrich-Alexander University of Erlangen-Nürnberg, Egerlandstraße 3a, D – 91058 Erlangen, Germany ° Saint-Petersburg State University, Institute of Chemistry, Universitetskii pr. 26, 198504 St. Petersburg, Russia

Resume : Perovskite solar cells have emerged in recent years as a potential low-cost technology for solar energy harvesting. Within only nine years of research the demonstrated performances climbed from 3.8% to above 22% certified efficiency. The deposition of high-quality perovskite thin films by solution processes such as blade and spin coating allows for the utilization of a wide range of planar and structured substrates. Titania nanotubes combine the advantageous high surface area of mesoporous TiO2 nanoparticular films with short, direct carrier pathways, thus facilitating charge extraction. Anodization is a versatile tool for the large-scale fabrication of nanotubes or pores on metal foils or thin films sputtered on FTO glass superstrates. The easy, independent tunability of structure and dimensions enables a conclusive in-depth study of the geometric effects on device performance. In this work, arrays of hexagonally arranged TiO2 nanotubes are employed as electron transport layers for nanostructured perovskite solar cells. The device structure is characterized after each processing step, and the performance of final devices is investigated by J-V curves, external quantum efficiency, and impedance spectroscopy. This system allows for systematic investigation of geometric effects on solar cell performance parameters.

Authors : Yangyang Wang, Tianhao Li, Seng Wang, Xianyu Deng*
Affiliations : Y.Y. Wang; T.H. Li; S. Wang; X. Y. Deng Shenzhen Key Laboratory of Advanced Materials, School of Materials Science and Engineering, Harbin Institute of Technology, Shenzhen, 518055, (PR China)

Resume : The film quality of perovskite is very crucial to the performance of perovskite solar cells. Here we present two methods on the growth of high quality perovskite films via a simple and rapid process. Polymer PAN and a series of hydrochlorides with different organic amine cations were introduced into CH3NH3PbI3 solution as an additive to obtain solar cells. Based on the high-quality films, a series of 2D materials and organic molecules as an interfacial layer makes perovskite solar cells with a planar heterojunction have largely enhanced open circiut voltage (Voc) and high power conversion efficiency (PCE) as well as a significant enhancement of stability.

Authors : C. Besleaga. L. Pintilie
Affiliations : National Institute of Materials Physics, 405 A Atomistilor street, PO Box MG 7, RO-077125, Magurele, Romania.

Resume : The impressive display market can maintain or even grow its prosperity only by investing in the improvement of the present state-of-the-art technology, lowering the costs and promoting new, environmentally friendly, materials. Here are intervening the OLETs as a possible next generation technology in the display industry. This type of devices can successfully combine the light emission of OLED with the switching of thin film transistors (TFT). The first room-temperature light-emitting diode based on organic-inorganic halide perovskite was reported in 2014 [1,2]. In both these two works, as well in other new studies the CH3NH3PbCl3, CH3NH3PbCl1.5Br1.5, CH3NH3PbBr3, CH3NH3PbBrI2 and CH3NH3PbI3 materials showed electroluminescence in the blue, green, red and near-infrared. But, the optimistic achievements reported these works are shaded by the use of lead in halide perovskite. The research concerning OLET based on halide perovskite is breaking new ground. There are very few published studies regarding the light-emitting TFT and, apparently, no TFT based on lead-free halide perovskite was reported yet. Here we report the fabrication of lead-free (CH3NH3)3Sb2I9-xClx thin films by three methods: i) modified one-step; ii) two-steps starting from spin-coated SbI3 film and iii) two-step starting from thermal evaporated SbI3 layer. Their structural, optical, morphological and electrical properties were analyzed and discussed. The optimized (CH3NH3)3Sb2I9-xClx layer was integrated in a TFT whose photo-electrical response was probed at room temperature. References: 1. Z.K. Tan et al., Nature Nanotechnol. 9 (2014) 687. 2. G. Xing et al., Nature Mater. 13 (2014) 476.

Authors : Qin Tan, Thomas Dittrich
Affiliations : Institute of Silicon Photovoltaics, Helmholtz-Center Berlin for Materials and Energy

Resume : Vacuum-assisted evaporation of solvents is a promising intermediate step for the controlled deposition of hybrid organic inorganic metal halide perovskite layers from salt solutions. The DMF:DMSO ratio, the components in the salt solutions, the temperature of the substrate during vacuum treatment (Ts) and the time of vacuum treatment (tv) were varied. The band gap and the tail states were characterized by modulated surface photovoltage spectroscopy and correlated with the current-voltage characteristics of solar cells. The band gap increased with decreasing DMF:DMSO ratio and, surprisingly, both Isc and Voc increased with increasing band gap. For CH3NH3PbI3, the optimum DMF:DMSO ratio, Ts and tv were 9:1, 30°C and 10s, respectively, and resulted in an efficiency above 17%. The dependence of the band gap of (CH3NH3)x(CH(NH2)2)1-xPbI3 on x was obtained. For mixed ion systems, a modified vacuum treatment including a purge with a pure gas is needed in order to reach high efficiencies.

Authors : Kyungmun Yeom1, Jun Hong Noh1,2*
Affiliations : 1School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 136-713, Republic of Korea 2Division of Advanced Materials, Korea Research Institute of Chemical Technology, 141 Gajeong-Ro, Yuseong-Gu, Daejeon 305-600, Republic of Korea. Fax: +82-(42)-3290-4866 E-mail address:

Resume : Halides such as CsPbI3, CH3NH3PbI3 and HC(NH2)2PbI3 have attracted many attentions in recent as innovative light absorbing materials in photovoltaic system. It is called halide perovskite solar cell (HPSC) because such halides have AMX3 perovskite crystal structure. Photovoltaic performance of HPSCs strongly depends on quality of the halide perovskite film. In particular, open circuit voltage (VOC) is determined by concentration of non-radiative recombination sites which lead to high voltage deficit that is a difference between optical band gap and qVOC. Therefore, the trap density in halide perovskite film should be minimized to obtain low voltage deficit. In this study, we propose a strategy of rapid crystallization of halide perovskite film to minimize voltage deficit instead of the conventional long annealing process to obtain high crystallinity of the film. We will discuss approach to obtain low voltage deficit by introducing short annealing process through control of crystallization behavior of halides.

Authors : Rajendra Adhikari
Affiliations : Kathmandu University, Dhulikhel, Kavre, Nepal

Resume : We conduct a systematic study on s, p and d (incomplete) electron atoms in different parts of Wurtzite crystl structure SnO2 for transparent electrode in perovskite solar cells. Next, we will study the bandgap alignment and possibaly 2D electron gas behavior at TiO2 interface at [100], [110] and [111] interface planes.

Authors : Yen-Sook Jung, Jun-Seok Yeo, Jae-Min Hong, Dong-Yu Kim
Affiliations : Institute of Advance composite Materials, Korea Institute of Science and Technology

Resume : Perovskite based on organic-inorganic metal halide has been highly attracted for solar energy conversion materials due to their superior properties such as high mobility, long diffusion length and high absorption co-efficiency. The efficiency of perovskite solar cells (PeSCs) has rapidly increased up to PCE of 22.1 % with developing various methods to modify perovskite morphology. We controlled the perovskite crystallization and morphology using binary processing additives, N-cyclohexyl-2-pyrrolidone (CHP) and 1,3-dimetyl-2-imidazolidinone (DMI) and fabricated highly efficient PeSCs via facial one-step process. CHP and DMI have higher basicity than DMF (dimethylformamide), which allows them to interact preferentially to Lewis acid base interaction with Pb. Therefore CHP and DMI affected crystallization and film morphology of perovskite during the crystal growth. The final perovskite film with CHP and DMI is highly oriented at azimuthal angle of 45 °, which facilitated charge transport from perovskite to hole transport layer. The best devices showed power conversion efficiency of 15.4 % and 12.26 % for devices fabricated by spin coating and slot die coating in optimized fabrication condition.

Authors : Damian Glowienka(a)(b), Francesco Di Giacomo(b), Mehrdad Najafi(b), Yulia Galagan(b), Jedrzej Szmytkowski(a)
Affiliations : (a) Faculty of Applied Physics and Mathematics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland (b) Holst Centre, Partner in Solliance High Tech Campus 21, Eindhoven 5656AE, The Netherlands;

Resume : Perovskite solar cells have attracted much attention in recent years due to their high efficiencies reaching values over 23% with application in tandem solar cells [1, 2]. However, the problem with perovskite solar cells is instability at high temperature and humidity which pose to be daunting in view of upscaling and application. Therefore, the recent research for improvement in stability has led to the conclusion that perovskite solar cells with mixed dual A-cation (2C) consists of formamidinium and cesium ions in perovskite layer have much better structural stability without loss of efficiency [3]. In the same kind of perovskite with sufficient cesium content, it has been reported that its charge carrier properties are not reduced when increasing bromide concentration [4]. Therefore, the 2C perovskite seems to be a good candidate for application in tandem solar cells with possibility to tune the bandgap by changing bromide and cesium content [5]. However, this raises a question what salt should be used to introduce bromide ions. Here, we investigate the three sources of bromide in the 2C perovskite Cs0.18Fa0.82Pb(I0.94Br0.06)3 absorption layer, meaning lead bromide (PbBr2), formamidinium bromide (FABr) and cesium bromide (CsBr). Using the same ion and mass concentration in the precursor, we have been able to compare the same perovskite composition made from the three different bromide sources. We analyze perovskite layer prepared with gas quenching and antisolvent method in the p-i-n device structure. Results of the following experiment have shown better performance for FABr and CsBr sources of bromide in comparison to regularly used PbBr2. Apart from the efficiency, the cells made with FABr as a bromide source for perovskite layer have also achieved best light stability at continuous MPP tracking compare to other composition. Our study will demonstrate long-term stability study at MPPT. The influence of bromide source on photovoltaic characteristics and long-term stability of the devices will be explained using structural, electrical and optical measurements. [1] D. Zhao, C. Wang, Z. Song, Y. Yu, C. Chen, X. Zhao, K. Zhu and Y. Yan, ACS Energy Lett. 2018, 3(2), 305?306. [2] Solliance Solar Research (2018, 21 March). Solliance and ECN take major step in improving tandem solar cells [Press release]. Retrieved from [3] J. W. Lee, D. H. Kim, H. S. Kim, S. W. Seo, S. M. Cho and N. G. Park, Adv. Energy Mater. 2015, 5(20), 1501310. [4] W. Rehman, D. P. McMeekin, J. B. Patel, R. L. Milot, M. B. Johnston, H. J. Snaith, L. M. Herz, Energy Environ. Sci. 2017, 10(1), 361?369. [5] K. A. Bush, K. Frohna, R. Prasanna, R. E. Beal, T. Leijtens, S. A. Swifter, M. D. McGehee, ACS Energy Lett. 2018, 3(2), 428?435.

Authors : Anirban Dutta, Narayan Pradhan*
Affiliations : Senior Research Fellow, Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India 7000322; Professor, Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India 700032

Resume : Cubic CsPbI3 perovskite nanocrystal is the next generation of materials for optoelectronic application, but this faces serious phase instability and transformed to nonemissive orthorhombic phase. Only a few approaches were reported to stabilize this cubic phase of the nanocrystals. All these approaches were based on heteroatom doping, using spatially designed ligands or following ice cool protocol. Success has been achieved in stabilizing these nanocrystals for few weeks in ambient atmosphere, but the problem of phase transformation during annealing in the reaction flask was not addressed. In contrary to that we have reported high-temperature colloidal synthesis for obtaining thermal, colloidal and phase stable CsPbI3 nanocrystals. The stability was achieved by introducing pre-formed alkylammonium salt and increasing the reaction temperature to 260 ᵒC. The pre-introduced alkylammonium ions at high-temperature passivate the surface firmly and prevented the nanocrystals from phase transformation. These nanocrystals were stable in reaction flask during annealing, in the crude reaction mixture in purified dispersed or in powder form. Details of the temperature gradient, the role of different parameters were investigated. Different spectroscopic analysis was carried out and details of the surface binding of alkylammonium ligands in place of surface Cs in the crystal lattice were investigated. As CsPbI3 is one of the most demanding optical materials, bringing stability by proper surface fictionalization without the use of secondary additives would indeed help in the wide spreading of their applications.

Authors : Samrat Das Adhikari, Narayan Pradhan*
Affiliations : SRF, Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India 700032 ; Professor, Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India 700032

Resume : Doped perovskite nanocrystals have recently emerged as a new class of energy materials for solar concentrators and solid-state lighting device applications. Among these, doping Mn(II) in high band gap CsPbCl3 perovskite host nanostructures has been extensively studied. However, going beyond their optical emissions, herein, the impact of dopant ions on tuning the doped platelet dimensions and retaining the monodispersity is reported. These were performed by designing appropriate compositions of layered perovskites, L2(Pb1–xMnx)Cl4, which on thermal treatment in the presence of Cs(I) ions transformed to Mn-doped CsPbCl3 platelets. Correlating the amount of Mn present in layered perovskites and retained in doped platelets, the role of Mn for the conversion of layered to doped perovskites was established. These doped platelets showed dominated Mn d–d emission and also Mn concentration-dependent emission tuning. Even though several reports of Mn-doped CsPbCl3 have been reported, these findings add new fundamental insight into the design of dimension-tunable doped perovskites from layered perovskites.

Authors : Ayesha Sultana†, Md. Mehebub Alam†, and Dipankar Mandal†,˦*
Affiliations : †Organic Nano-Piezoelectric Device Laboratory, Department of Physics, Jadavpur University, Kolkata 700032, India ˦Institute of Nano Science and Technology (INST), Phase-10, Sector-64, Mohali-160062, India ‡ Department of Instrumentation Science, Jadavpur University, Kolkata 700032, India *Corresponding Author E-mail:

Resume : Towards hybridized renewable energy harvesting systems, improvement of suitable materials is needed so that they can be used as self-powered portable electronic systems.1 In this work, methylammonium lead iodide (MAPI) is synthesized via co-precipitation method and used to nucleate -phase in polyvinylidene fluoride (PVDF) films.2 We found that MAPI not only nucleates electroactive phase (up to ~ 91 % ) in PVDF but it also gets stabilized in ambient condition. The piezoelectric energy generation from composite film of MAPI and PVDF is presented under simple human finger touch motion. The hybrid photoactive energy harvester can simultaneously harvest mechanical energy and detect visible light. The fast rising time as well as fast increase in current under non-monochromatic light illumination is detected which is a signature to use as an efficient photoactive device. On account of the photoresponsive and electroactive characteristic of the composite film a new class of stand-alone self-powered flexible hybrid photoactive mechanical energy harvester is made. A significant change of piezoelectric output voltage and current is observed during the visible light detection that promises its futuristic application in piezo-phototronic technology. REFERENCES [1] A. Sultana et al., ACS Appl. Mater. Interfaces 2015, 7, 19091. [2] D. Mandal et al., J. Phys. Chem. B 2011, 115, 10567.

Authors : Karsten Henkel, Małgorzata Kot, Dieter Schmeißer
Affiliations : Brandenburg University of Technology Cottbus-Senftenberg, Applied Physics and Sensor Technology, K.-Wachsmann-Allee 17, 03046 Cottbus, Germany

Resume : The characterization of intrinsic defect mechanisms in Al2O3 thin films is essential for their effective use in surface passivation schemes for solar cells. Particularly, perovskite solar cells (PSC) have shown an enhanced long-term stability and an improved protection against ambient conditions when an ALD-Al2O3 layer is introduced into the PSC stack [1]. In this work, we discuss comparatively ALD-Al2O3 films prepared on different substrates (including MAPI: CH3NH3PbI3) and by different process parameters (thermal-ALD, plasma-enhanced-ALD, substrate temperature). These films were analyzed by resonant photoelectron spectroscopy. Intrinsic defect states within the electronic band gap were observed including excitonic, polaronic, and charge-transfer defect states, where their relative abundance depends on the choice of the used ALD parameters and substrate [2,3]. The most pronounced signature of excitonic states is found for the Al2O3 film prepared on MAPI at room temperature. It points to a strong distortion of the octahedral coordinated network with a high number of tetrahedral sites which have a high affinity for OH adsorption and , hence, are responsible for perovskite protection against humidity [2]. [1] M. Kot et al., ChemSusChem 9 (2016) 3401. [2] K. Henkel, M. Kot, D. Schmeißer, J. Vac. Sci. Technol. A 35 (2017) 01B125. [3] K. Henkel, M. Kot, M. Richter, M. Tallarida, D. Schmeißer, in K. Wandelt (Ed.): Encyclo-pedia of Interfacial Chemistry: Surface Science and Electrochemistry, Elsevier, Oxford, 2018, vol. 3.1, pp 18-26.

Authors : Malgorzata Kot1, *, Lukas Kegelmann2, Peter Kus3, Nataliya Tsud3, Iva Matolinova3, Steve Albrecht2, Vladimir Matolin3 and Dieter Schmeißer1
Affiliations : 1Brandenburg University of Technology Cottbus–Senftenberg, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstraße 5, 12489 Berlin, Germany 3Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic *Corresponding author e-mail address:

Resume : Since few years, many efforts have been done to keep the initial efficiency of the perovskite solar cells over a long time. The CH3NH3PbI3-based solar cells have shown an increased long-term stability against ambient conditions while encapsulating them or covering the perovskite film by a thin Al2O3 film. Although the solar cells stability with the Al2O3 film could be successfully improved it has not lasted for a long time. In this paper, we will present that by covering the CH3NH3PbI3 film with a room temperature atomic layer deposited Al2O3 (RT-ALD-Al2O3) [1,2] one cannot only increase the stability, but more interestingly, one can boost the efficiency of solar cells over time. In particular, the Al2O3/CH3NH3PbI3 interface is characterized using the X-ray Photoemission Spectroscopy (XPS) and Field Emission Scanning Electron Microscopy (FESEM). The efficiency of the Au/Spiro-OMeTAD/(RT-ALD-Al2O3)/CH3NH3PbI3/PCBM/TiO2 /ITO/glass solar cells are extracted from the current density-voltage (J-V) characteristics measured under AM1.5G light at 100 Wcm-2. As deduced from the XPS and FESEM studies the ALD precursors only clean the perovskite surface from the –OH groups and do not change its composition. Most importantly, the average efficiency of the solar cells containing 9 RT-ALD-Al2O3 cycles increases from 9.4 to 10.8 % but without the RT-ALD layer it decreases from 13.6 to 9.6 % while storing both in the same environmental conditions for 355 days. [1] M. Kot et al., ChemSusChem 9 (2016) 3401. [2] M. Kot et al., Nucl. Instrum. Methods Phys. Res. B 411 (2017) 49.

Authors : Chittaranjan Das1, Michael Wussler1, Nils Wagner1, Thomas Mayer1 and Wolfram Jaegermann1 Andreas Binek 2 and Thomas Bein2
Affiliations : 1. Technical University Darmstadt, Department: Surface science, Germany 2. LMU München, Bein Research Group: Functional Nanosystems, Germany

Resume : The electronic properties of the perovskites change itself depending on the synthesis methods and the substrates on which they are grown and hence the performance of the device [1 ]. Therefore it is of prime importance to study the electronic properties of the perovskite in order to choose the proper contact materials and optimized solar cell performance. In literature it is discussed that a mixture of the methylammonium (MA) and formamidinium (FA) halide based perovskite are efficient and stable compare to single organic cation based perovskite[ 2]. In the present work we investigated the electronic properties of mixed organic cation perovskite. In particular we conducted the photoemission study on different percentage of the FA and MA in the mixed perovskite and measured the valence band and work function. It is found that the change is electronic structure is minimal in case of FAxMA(1-x)PbI3 upon variation of FA and MA concentration while in FAxMA(1-x)PbBr3 it is larger. In FAxMA(1-x)PbBr3 the value of x=0 to 1 changes the valence band maxima of perovskite form 1.39 eV to 1.97 eV. We believe this finding can be helpful to properly design the perovskite based multijunciton solar cell as well as to choose the proper contact materials for optimum efficiency . 1. S. Olthof and K. Meerholz, Sci. Rep. 2017, 7, 40267. 2.N. Pellet P. Gao, G. Gregori, T-Y. Yang M. K. Nazeeruddin, J. Maier and M. Grätzel, Angew. Chem. Int. Ed. 2014, 53, 3151 ?3157.

Authors : Lokeshwari Mohan, Joe Briscoe, Martyn A. McLachlan, Russell Binions
Affiliations : Department of Materials and Centre for Plastic Electronics, Imperial College London, South Kensington, London SW7 2AZ, United Kingdom; School of Engineering and Materials Science and Materials Research Institute, Queen Mary University of London, Mile End Road, London E14NS, United Kingdom

Resume : Copper (l) thiocyanate (CuSCN) is an optically transparent, wide bandgap (3.4-3.9 eV), p-type semiconductor used in organic and perovskite solar cells. In comparison to other hole transporting materials, CuSCN is economically favourable and comparable in performance, with efficiencies for hybrid organic-inorganic metal halide perovskite solar cells exceeding 20% [1]. Current research involves several solution-processable methods such as spin coating, spray coating and doctor blading. This study reports the first ever synthesis of CuSCN via aerosol assisted chemical vapour deposition (AACVD). AACVD is a scalable technique with low processing costs, simple reactor design and no vacuum requirement. The study involves deposition of CuSCN using four different solvents; diethyl sulfide, dipropyl sulfide, diethyl methyl sulfide and ammonium hydroxide. For each CuSCN/ solvent combination, deposition temperature, concentration of solution and amount of precursor solution deposited were altered. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy were used to determine morphological, structural and optical information. [1] N. Arora, M. I. Dar, A. Hinderhofer, N. Pellet, F. Schreiber, S. M. Zakeeruddin and M. Grätzel, Science, 2017.

Authors : Marcin Saski a, Daniel Prochowicz ab, Michael Grätzel b, Janusz Lewiński ac
Affiliations : a Institute of Phisical Chemistry Polish Academy of Sciences , Kasprzaka 44/52, Warsaw (Poland) b Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, School of Basic Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne (Swieterland) c Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, Warsaw, Poland

Resume : We present a facile mechanochemical route for the preparation of organolead halide perovskites, where the chemical reactions are forced by high energy ball mill. Advantages of this methods include fast reaction time, high product purity and avoiding toxic organic solvents (producing less waste). Powder X-ray diffraction measurements demonstrate that mechanosynthesis is a suitable strategy to produce a highly crystalline material showing no detectable amounts of the starting substrates. Here we report a facile mechanochemical route for: (a) preparation of MAPbI3 and other two component materials (b) the stabilization of a structurally stable α-FAPbI3 perovskite by fine and controllable stoichiometry modification in mixed-cation (MA)x(FA)1−xPbI3 perovskites, (c) the first time atomic-level evidence that guanidine cation is directly incorporated into the MAPbI3 and FAPbI3 lattices, forming pure GUAxMA1–xPbI3 or GUAxFA1–xPbI3 phases. The following materials were used to manufacture perovskite solar cells with extraordinary efficiencies reaching 20%. 1) D. Prochowicz, M. Franckevičius, A. M. Cieślak, S. M. Zakeeruddin, M. Grätzel, J. Lewiński, Journal of Materials Chemistry A, 2015, 3, 20772–20777 2) D. Prochowicz, Y. P. Kumar, M. Saliba, M. Saski, S. M. Zakeeruddin, J. Lewiński, M. Grätzel, Sustainable Energy and Fuels, 2017, 1, 689–693 3) D. Prochowicz, P. Yadav, M. Saliba, M. Saski, S. Zakeeruddin, J. Lewinski, M. Grätzel, ACS Applied Materials & Interfaces, 2017, 34, 28418–28425 4) D. Kubicki, D. Prochowicz, A. Hofstetter, M. Saski, P. Yadav, D. Bi, N.Pellet, J. Lewinski, S.M. Zakeeruddin, M. Grätzel, L. Emsley, Journal of the American Chemical Society, 2018, 140, 3345–3351

Authors : Rokas Gegevičius, Marius Treideris, Marius Franckevičius, Vidmantas Gulbinas
Affiliations : R. Gegevičius; Dr. M. Treideris; Dr. M. Franckevičius; Prof. V. Gulbinas Center for Physical Sciences and Technology, Saulėtekio Av. 3, LT-10257 Vilnius, Lithuania

Resume : It is nearly eight years since the hybrid perovskites have attracted the significant interest of the scientific community, mainly due to the outstanding performance of hybrid perovskite solar cells. A high achievable efficiency of the perovskite-based solar cells, currently reaching 22%, [1] shows that carrier generation efficiency in perovskites may approach 100%, suggesting that perovskites may be promising materials not only for solar cells but also for sensitive photodetectors, which may compete with conventional semiconductor analogs. Despite tremendous interest in solar cell research perovskite photodetectors still lack a basic understanding of their operating principles. Here, we study the performance of planar polycrystalline MAPbI3 perovskite photodetectors produced on interdigitated comb of electrodes made from various metals. We demonstrate that a hole blocking oxide layer between metal electrodes and perovskite may enhance responsivity and photocurrent gain of the planar photodetector based on the polycrystalline film by order of magnitude. Application of the Cr interdigitated comb of electrodes with naturally formed oxide layer enabled to reach resposivity of 152 A/W an external gain of more than 350. We suggest that the gain enhancement originates from the hindered extraction of photogenerated holes and the migration of ions, which creates additional hole traps at interfaces. These effects reduce the barrier for electron injection and enable the passage of a larger number of electrons during the prolonged lifetime of photogenerated holes. The achieved photodetector sensitivity, suggested gain enhancement approach and obtained better understanding of the photocurrent gain mechanism in hybrid metal halide perovskites open a way towards the further development of a cheap and easily producible planar perovskite photodetectors based on interdigitated electrode arrays. Reference [1] National Renewable Energy Laboratory. Best Research-Cell Efficiencies. Available at Accessed on 21 May 2018

Authors : Yan Fong Ng, Sneha A. Kulkarni, Shayani Parida, Nur Fadilah Jamaludin, Natalia Yantara, Annalisa Bruno, Cesare Soci, Subodh Mhaisalkar, Nripan Mathews
Affiliations : Nanyang Technological University, Singapore

Resume : Halide perovskites have established themselves as a promising semiconductor material for light-emitting diodes (LEDs), challenging the state-of-the-art organic and quantum dot LEDs. While three-dimensional (3D) perovskites (APbX3 where A = MA or FA and X = I, Br or Cl) suffer from low photoluminescence quantum yield due to small exciton binding energies and non-radiative recombination arising from trap states, quasi-2D perovskite structures derived from intercalating large organic counter-cations within the lead halide networks have recently been found to overcome such problems. However, the organic-based (MA and FA) perovskites are known to have poor thermal stability. This work presents the first study of a quasi-2D perovskite based on the inorganic and more thermally resistant CsPbBr3 compound. The incorporation of a large alkylated molecule – phenylethylammonium bromide (PEABr), into the CsPbBr3 framework is shown to yield huge improvement to the photophysical and morphological properties of the perovskite film. By carefully tuning the molar addition of PEABr, highly compact, smooth and nano-sized grains were achieved with efficient energy funneling through an energy cascade as proven by various spectroscopic analyses. The benefits are well reflected in LEDs made from this quasi-2D mix, giving more than 50-fold increment in luminance and efficiency. The simplicity of this approach allows ample opportunity for large-scale production.

Authors : Benny Febriansyah, Teck Ming Koh, Rohit Abraham John, Rakesh Ganguly, Li Yongxin, Annalisa Bruno, Subodh G. Mhaisalkar, Jason England.
Affiliations : Benny Febriansyah (Energy Research Institute at NTU, Interdisplinary Graduate School, Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences); Teck Ming Koh (Energy Research Institute at NTU); Rohit Abraham John (Energy Research Institute at NTU, School of Materials Science and Engineering); Rakesh Ganguly (Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences); Li Yongxin (Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences); Annalisa Bruno (Energy Research Institute at NTU); Subodh G. Mhaisalkar (Energy Research Institute at NTU, School of Materials Science and Engineering); Jason England (Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences).

Resume : As a consequence of their quantum- and electronically-confined inorganic lattices, 1D lead-iodide perovskites are ill suited to photovoltaic (PV) applications. In order to circumvent these problems we utilized electron accept-ing viologen (N,N'-dialkyl-4,4'-bipyridinium) dications incorporating hydrogen bond donor functionalities, which served to induce π-π stacking interactions. The resulting 'viologen dimers' display enhanced charge-transfer (CT) interactions with the 1D lead-iodide nan-owires. This manifests in extended light absorption (up to 800 nm), reduced band gaps (1.74 eV to 1.77 eV), and longer photoluminescence lifetimes. More importantly, we demonstrate significant photoconductivity behavior in polycrystalline 1D lead-iodide perovskites for the first time. Thus, this work offers a strategy for inducing the properties required for PV applications in 1D lead-iodide perovskites.

Authors : Xiaolu Zheng, Yulong Wang, Hongwei Lei, Guang Yang, Zongxiang Xu*, Guojia Fang*
Affiliations : Guojia Fang, Xiaolu Zheng, Hongwei Lei, Guang Yang Key Lab of Articial Micro- and Nano-Structures of Ministry of Education of China, School of Physics and Technology, Wuhan University, Wuhan 430072, P. R. China. E-mail: Zongxiang Xu, Yulong Wang, Department of Chemistry, South University of Science and Technology of China, Shen Zhen, Guangdong 518055, P. R. China. E-mail:

Resume : Organo-lead halide perovskite solar cells (PSCs) have attracted tremendous attention owing to their superior photovoltaic properties. However, despite the excellent power conversion efficiencies (PCEs) that have recently been achieved, the device stabilities are still a challenge for the commercialization of PSCs. Spiro-OMeTAD is a widely used hole transport layer (HTL) in conventional n-i-p PSCs, which has been reported to suffer degradation from the permeate of moisture due to the hygroscopic additive and the presence of pinholes. To fix the relatively low device stability of PSCs based on spiro-OMeTAD, numerous strategies have been developed and applied in PSCs. One approach to diminishing these adverse effects introduced by the moisture permeate and ion migration is to insert a buffer layer. To avoid decreasing the device performance while improving the stability, this p-type semiconductor needs possess high conductivity and superior hole mobility besides hydrophobicity. Lead sulphide (PbS) is a traditional direct bandgap semiconductor with high hole mobility. We found that when inserting a thin layer of PbS between the metal electrode and spiro-OMeTAD, the PSCs with PbS buffer layer exhibited a better photovoltaic performance and significantly enhanced stability with respect to the reference cells. The superior hole mobility of spiro-OMeTAD/PbS bilayer was considered to be the dominated origin of the device performance improvement. And the hydrophobic nature and dense morphology of PbS enable it to provide an efficient permeation barrier against moisture and metal migration. The champion cell with PbS buffer layer displayed a PCE of 19.58% and maintained almost 100% of its initial PCE after 1000 h stored in ambient air. While in this structure the spiro-OMeTAD is still requisite. Metallophthalocyanine (MPc) compounds that consist of an 18-π electron conjugated macrocycle skeletal structure are potential candidates for stable HTLs in PSCs. We reported a novel heavy atom Pc derivative, octamethyl-substituted palladium(II) phthalocyanine (PdMe2Pc), which shows promise as an HTL in PSCs. The introduction of the heavy Pd atom endows the material with a long carrier lifetime and without dramatically reducing its mobility. This PdMe2Pc exhibited a long carrier diffusion length (LD) which is benefit to reducing the charge recombination. The devices based on PdMe2Pc displayed a relatively high PCE of 16.28% and good long-term stability.

Authors : Annalisa Bruno, Herlina Arianita Dewi, Wang Hao, K. Vergeer, Li Jia, Maung Thway, Lin Fen, Rolf Stangl, Armin Aberle, Nripan Mathew, Subodh Mhaisalkar
Affiliations : Energy Research Institute@Nanyang Technological University, Singapore. SERIS, National University of Singapore, Singapore. School of Materials Science and Engineering, NTU, Singapore

Resume : The photovoltaic (PV) market is dominated by silicon solar cells (SCs) delivering high efficiency and long-term stability. However, Si SCs are approaching their efficiency limit and new methodologies are required to overcome it. Tandem SCs, combining Si SCs with a low-cost wide-band-gap absorber material as perovskite, that absorb light in a complementary solar spectrum region, are the most promising option for improving existing PV technologies keeping the production cost low.1 The implementation of highly efficiency semi-transparent perovskite SCs is a critical issue to reach this goal. In this work we present tandem structures using semi-transparent perovskite top-cell and silicon SCs as bottom cell reaching efficiency above 23% in a 4-terminals mechanical stack configuration. Semitransparent perovskite SCs with efficiency above 16.0% efficiency and average transparency >70% in near-infrared, have been realized using indium tin oxide (ITO) as transparent electrode and a thin Ag layer to protect the organic layers and to guarantee a resistant to delamination contact.2 Here we also compare SCs realized both by spincoating and thermal evaporation and we discuss the effects of perovskite bandgap on tandem SCs efficiency. 1. J Werner, et al., Adv. Mater. Interfaces 2018, 5, 731; Y Wu et al., En. Environ. Sci., 2017,10, 2472; K.Bush, et al. Nature Energy volume 2, 17009 (2017); T. Duong, et al. Adv. Energy Mater. 2017, 7, 228. 2. A. Guchhait et al ACS Energy Lett. 2, 4, 807-812

Authors : Yamilova O.R.(1,2), Luchkin S.Yu.(3), Mangrulkar M.(3), Fedotov Yu.S.(4), Bredikhin S.I.(4), Troshin P.A.(3,1)
Affiliations : (1) Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia; (2) Lomonosov Moscow State University, Moscow, Russia; (3) Skolkovo Institute of Science and Technology, Moscow, Russia; (4) Institute of Solid State Physics of RAS, Chernogolovka, Russia

Resume : Perovskite solar cells demonstrated impressive power conversion efficiencies of >22%, while their practical application is hampered by poor stability of the active materials. Functional layers of perovskite solar cells have to sustain electric fields generated by built-in and light-induced potentials. Otherwise, the electrochemical degradation of active or charge transport layer materials would ruin the solar cell performance. In this work, we report a systematic comparative study of the electrochemical stability of a series of hybrid and all-inorganic lead halide based perovskite materials - MAPbI3, MAPbBr3, FAPbI3, FAPbBr3, CsPbBr3, CsPbI2Br. Thin films of these materials were exposed to the potentiostatic polarization under anoxic conditions using the lateral and vertical two-electrode device architectures. We have shown that polarization leads to the appearance of the field-induced gradients in the chemical composition of the films as revealed by PL and Kelvin probe microscopy and ToF-SIMS. The effects of the potentiostatic polarization of the solar cells under forward and reversed bias on their photovoltaic performance will be also discussed and interpreted using results of the light beam induced current (LBIC) mapping. Analysis of the obtained data allowed us to correlate the chemical composition of the perovskite materials with their electrochemical stability, which might guide further design of stable light absorbers for future generation photovoltaics.

Authors : Azat F. Akbulatov (1)*, Nadezda N. Dremova (1), Sergey Yu. Luchkin (2), Sergey A. Tsarev (2), Moneim Elshobaki (2), Ernst Z. Kurmaev (3,4), Vyacheslav M. Martnenko (1) and Pavel A. Troshin (2,1)
Affiliations : 1 Institute for Problems of Chemical Physics of RAS, Semenov ave. 1, Chernogolovka, Moscow region, 142432, Russia; 2 Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Nobel st. 3, Moscow, 143026, Russia; 3 Institute of Physics and Technology, Ural Federal University, Mira st. 19, Yekaterinburg, 620002, Russia; 4 M. N. Mikheev Institute of Metal Physics of Ural Branch of Russian Academy of Sciences, S. Kovalevskoi st. 18, Yekaterinburg, 620990, Russia

Resume : Lead halide based perovskite solar cells have progressed significantly with the efficiency rising from 3.8% to over 22% within a few years. However, the use of toxic Pb derivatives severely limits niches for their application and commercialization. Less harmful tin (Sn), bismuth (Bi) and antimony (Sb) derivatives are considered now as environment friendly alternatives. Here we present a systematic study of thermal and photochemical degradation pathways of a series of complex halides ASnX3, A3Bi2X9 and A3Sb2X9 (X=I, Br) with organic (A+= CH3NH3+, H2NCHNH2+) and inorganic (A+=Cs+) cations under inert anoxic conditions by using a set of complementary techniques: optical spectroscopy, AFM and SEM microscopy, XPS, XRD, EDX microanalysis and mass spectrometry. It has been shown that hybrid perovskite materials incorporating organic cations are intrinsically unstable under the realistic solar cell operation conditions and undergo dramatic changes in their optical, morphological and structural properties. On the contrary, cesium-based all inorganic complex metal halides showed much superior stability. Unfortunately, none of the investigated materials demostarted improved photochemical stability in comparison with the conventional complex lead halides. Nevertheless, the analysis of the comprehensive set of the obtained results creats a solid background for rational design of the next generation light absorbers for efficient and durable perovskite-inspired solar cells.

Authors : L.A. Frolova,1,2 A. F. Akbulatov, 2 S.Yu. Luchkin,1 S.A.Tsarev,1 N.N. Dremova,2 K.J. Stevenson1 and P.A. Troshin1,2
Affiliations : 1 Skolkovo Institute of Science and Technology, Nobel st. 3, Moscow, Russia 2Institute for Problems of Chemical Physics of RAS, Chernogolovka, Moscow region, Russia *e-mail:

Resume : Hybrid perovskite solar cells have attracted a considerable attention of researchers due to feasibility of their low-cost production and achieving impressive power conversion efficiencies of >22%. Currently, low operation stability of hybrid perovskite solar cells represents the main obstacle for their practical implementation. Replacing fragile organic moieties with robust inorganic cations represents a promising approach to designing some more stable absorber materials. Inorganic lead-halide based perovskites CsPbI3-xBrx (x=0-3) have demonstrated improved thermal and photochemical stability. Unfortunately, the photovoltaic performances of all-inorganic perovskites remain much infeior in comparison with conventional hybrid materials and suffer from severe phase stability issues (e.g. perovskite phase of CsPbI3 is thermodynamically unstable at room temperature). To overcome these obstacles, more research is needed. Here we report a detailed investigation of all-inorganic perovskite-inspired systems based on CsxPbI2Brx alloys with x ranging from 1 to 4. An optimal non-stoichiometric composition has been identified, which delivered the best optoelectronic, structural and photovoltaic characteristics in combination with the improved stability. The revealed remarkable effect of excessive CsBr on the photothermal stability and photovoltaic performance of CsPbI2Br perovskite films might create a new paradigm in the development of efficient and stable solar cells.

Authors : Dr. Shuxia Tao1, Dr. Ionut Tranca2, Ines Schmidt3, Dr. Selina Olthof3, Prof. Klaus Meerholz3
Affiliations : (1) Center for Computational Energy Research, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513 5600 MB Eindhoven, the Netherlands (2) Energy Technology, Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands (3) Institute of Physical Chemistry, Department of Chemistry, University of Cologne, Luxemburgerstrasse 116, 50939 Cologne, Germany

Resume : In just a few years, perovskites solar cells (PSCs) have emerged as one of the most promising solar cell technologies. So far, the PCEs of PSCs above 22% have been reported, which is rivalling values achievable with crystalline silicon solar cells. In spite of the fast growth in the photovoltaic performance, PSCs are severely limited in their large scale applications due to instability issues. These include intrinsic instabilities of the metal halide perovskites, environmental instabilities, and device operation related instability. In this work, the first issue, i.e. intrinsic instability of the metal halide perovskite is studied by combing chemical bonding analysis of DFT calculations and experimental degardation study using Ultraviolet–visible spectroscopy. A comprehensive set of chemical bonding analysis of DFT calculations are done for AMX3 (A=Cs, MA, FA, M=Pb, Sn, X=I, Br, Cl) perovskites. Bond order, net charge, steric repulsion, and Crystal Orbital Hamilton Population (COHP) analysis reveal the relation of covalent, ionic, steric interactions, as well as bonding/antibonding characters with their stability, respectively. As a part of this work, Ultraviolet–visible spectroscopy of AMX3 perovskites film degradation during incremental heating were carried out to probe their thermal stability. A systematic comparison of the theoretical analysis and experimental data points to the most important factors responsible for the trends in the thermal stability of AMX3 perovskites. This sets of chemical bonding analysis also shows promise (from our preliminary study) in explaining the structural instability of metal halide perovskites, i.e. transition of black phase (3D structure) to yellow phase (2D structure).

Authors : Zahra Heydari, Hamed Abdy, Arash Aletayeb, Mohammadreza Kolahdouz, A. Valinejad, Amir Hossein Karami, Ebrahim Asl-Soleimani
Affiliations : School of Electrical and Computer Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran.

Resume : Perovskite solar cells (PSCs) has raised hopes for a technological revolution in the field of photovoltaics. However, fabrication parameters should be investigated carefully to achieve optimum PSCs. In this work, the effects of electron transport layer (ETL) thickness, purity of solvents and precursor materials, methods of perovskite synthesis, and type of hole transporting material (HTM) are studied as some of the most important fabrication factors. We found that the performance of the PSC is strongly influenced by the purity of the precursors and solvents. Using precursor materials synthesized in our lab and conventional solvents we could not reach efficiencies more than %1.47, but replacing precursors with high purity commercial ones and using anhydrous solvents easily improved our results up to %4.11. The quality of ETL highly affects the quality and reproducibility of fabricated solar cells. Our experiments show that spin coating of TiO2 as ETL (blocking layer) for two times yields better and more reproducible results. Using a mesopore TiO2 layer is also beneficial. We also tried to use the sputtering method for coating the NiO layer as hole transport material, which showed that even the least sputtering power could damage and degrade the perovskite films. A comparison on two step spin coating and electrodeposition methods for perovskite synthesis were also done which shows morphological superiority of perovskite layer deposited using electrodeposition method.

Authors : Taisuke Matsui,1 Ieva Petrikyte,2 Tadas Malinauskas,2 Konrad Domanski,3 Maryte Daskeviciene,2 Matas Steponaitis,2 Paul Gratia,4 Wolfgang Tress,3 Juan-Pablo Correa-Baena,5 Antonio Abate,3 Anders Hagfeldt,5 Michael Graetzel,3 Mohammad Khaja Nazeeruddin,5 Vytautas Getautis,*2 Michael Saliba,*3,4
Affiliations : 1 Advanced Research Division, Materials Research Laboratory, Panasonic Corporation, 1006 Kadoma, Kadoma City, Osaka 571-8501, Japan; 2 Department of Organic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, Kaunas, 50254, Lithuania; 3 Laboratory of Photonics and Interfaces, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland; 4 Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland; 5 Laboratory of Photomolecular Science, Station 6, CH-1015 Lausanne, Switzerland.

Resume : Rapid development of technologies and their influence on people's lives is increasingly associated with energy demand. In order to meet this growing energy demand and minimize related costs new and effective energy generation methods are necessary. Among several alternative sources, photovoltaics are among the most promising, as solar energy is free and inexhaustible energy source. Perovskite solar cells often consist of several layers, each having a specific function and made of materials that meet a certain set of requirements. Some of those requirements include the stability issue, which derives from additives that are used in the process of increasing the conductivity of hole transporting materials. Having that in mind triarylamine derivative polymers with different functional groups were synthetized as hole transport materials (HTMs) for perovskite solar cells (PSCs). The novel materials enabled efficient PSCs without the use of chemical doping to enhance the charge transport. Devices employing poly(triarylamine) with methylphenylethenyl functional groups showed better power conversion efficiency then widely used additive-free compound - poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). Notably, devices with the foremost polymer enabled stable PSCs under 1 sun at maximum power point tracking for ~40 hours and under elevated temperature (85 °C) for more than 140 hours. The results present remarkable progress towards stable PSC under real working conditions, which is crucial for industrial application

Authors : K. Juraić (1), I. Panžić (1), Domagoj Belić (1), D. Meljanac (1), K. Salamon (1), A. Šantić (1), M. Plodinec (2), T. Rath (3), G. Trimmel (3), A. Gajović (1)
Affiliations : (1) Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia (2) Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany (3) Institute for Chemistry and Technology of Materials (ICTM), NAWI Graz, Graz University of Technology, Stremayrgasse 9, 8010 Graz, Austria

Resume : One of the methods to improve perovskite solar cells (PSC) performance is to change the mesoporous titania (TiO2) structure to a more ordered one, e.g. to nanorod or nanotube arrays. Oriented nanorod-like materials on transparent conductive oxide (TCO) are known for their efficient charge separation and transport properties and are thus favourable for achieving good device performance. Recently we have reported successful preparation of vertically aligned TiO2 nanotube (NT) array thin film for photovoltaic application by electrochemical anodization of titanium layer deposited by magnetron sputtering (V. Mandic et al. Solar Energy Materials and Solar Cells 168 (2017) 136–145). If the duration of anodization process is not set optimally, obtained TiO2 NT layer will not have satisfying transparency or will have deep holes that continue in TCO layer underneath which can cause bad performance of PSC. In this work, we propose the use of very thin TiO2 buffer layer in-between TCO and TiO2 NT layer to minimize this problem. TiO2 buffer layer will be deposited by DC reactive magnetron sputtering using titania target and Ar O2 working gas mixture followed by titania layer deposition. Structural, optical and electrical propertis of the improved composite TiO2 NT electrode will be compared to standard one. Influence on PSC performance will be also disused. Acknowledgement to Croatian science foundation (project ZOTONanoPhotovolt 2014-09-9419) for financial support.

Authors : Wouter Van Gompel ; Roald Herckens, Gunter Reekmans ; Peter Adriaensens ; Laurence Lutsen ; Dirk Vanderzande
Affiliations : IMEC – IMOMEC – Wetenschapspark 1, B-3590 Diepenbeek, Belgium. Hasselt University, Institute for Materials Research (IMO), Organic and Biopolymer Chemistry (OBPC), Agoralaan - Building D, B-3590 Diepenbeek, Belgium

Resume : The highest efficiency in perovskite solar cells is currently achieved with mixed-cation hybrid perovskites. The ratio in which the cations are present in the perovskite structure has an important effect on the optical properties and the stability of these materials. The incorporation of formamidinium into hybrid perovskites has proven beneficial in terms of stability as well as efficiency. Indeed, the highest efficiency lab-scale devices currently contain a certain percentage of the formamidinium cation. Therefore this system was chosen for an in-depth NMR study. Formamidinium-methylammonium lead iodide phases (FAxMA1-xPbI3) with different FA/MA ratios were prepared. Powders obtained via a precipitation method were compared with powders obtained by scarping off films. The powders were analyzed using X-ray diffraction and 1H-, 13C- and 207Pb solid–state NMR. The incorporation of formamidine and methylamine in the hybrid perovskite crystal lattice can be derived from differences in relaxation behavior compared to the precursor salts. The 207Pb resonance peak shifts systematically with the FA/MA ratio present in the powders.

Authors : Yasir Saeed
Affiliations : Department of physics, Abbottabad University of Science Technology, Abbottabad, KPK, Pakistan.

Resume : The double perovskites Cs 2 AgBiCl 6 and Cs 2 TlSbCl 6 have been investigated using all-electron full-potential linearized augmented plane wave (FP-LAPW+lo) method within the frame work of the density functional theory. In addition to this, we employed Modified Back-Johnson bandgap correction in order to obtained close value of gap with respect to the experimental value. Our obtained bandgap is 2.66 eV (Cs 2 AgBiCl 6 ) and 1.466 eV (Cs 2 TlSbCl 6 ) with spin orbit coupling. Cs 2 AgBiCl 6 has indirect (L ? X) bandgap while our hypothetical Cs 2 TlSbCl 6 shows direct bandgap at ?-point. We have calculated phonon band structure for both studied compounds and found positive frequencies, which shows the stability. Stable, direct bandgap and value of gap close to MAPI makes Cs 2 TlSbCl 6 a great competitor in Pb-free hybrid perovskites solar cell word.

Authors : Junke Jiang 1, Chidozie K. Onwudinanti 2, Ross A. Hatton 3, Peter A. Bobbert 4,1, Shuxia Tao 1
Affiliations : 1 Center for Computational Energy Research, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513 5600 MB Eindhoven, The Netherlands; 2 Center for Computational Energy Research, DIFFER – Dutch Institute for Fundamental Energy Research, De Zaale 20, 5612 AJ Eindhoven, The Netherlands; 3 Department of Chemistry, University of Warwick, CV4 7AL, Coventry, United Kingdom; 4 Molecular Materials and Nano Systems, Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513 5600 MB Eindhoven, The Netherlands.

Resume : Due to its thermal stability, lead-free composition and nearly ideal optical and electronic properties, orthorhombic CsSnI3 perovskite is considered promising as a light absorber for lead-free all-inorganic perovskite solar cells (PSCs). However, the susceptibility of this 3-dimensional perovskite towards oxidation in air has limited the development of solar cells based on this material. Here, we report the findings of a computational study which identifies promising RbyCs1-ySn(BrxI1-x)3 perovskites for solar cell applications, prepared by substituting cations (Rb for Cs) and anions (Br for I) in CsSnI3. We show the evolution of the material’s electronic structure, as well as its thermal and structural stabilities upon gradual substitution. Importantly, we demonstrate how the unwanted yellow phase can be suppressed by substituting Br for I in CsSn(BrxI1-x)3 with x >1/3. We predict that substitution of Rb for Cs results in a highly homogeneous solid solution and therefore an improved film quality and applicability in solar cell devices.

Authors : Subha Sadhu1,2, Thierry Buffeteau1, Kyler Aqueche1, Dario Bassani1, and Lionel Hirsch2
Affiliations : 1Université Bordeaux CNRS UMR 5255, ISM, F-33405 Talence, France, 2Université Bordeaux, CNRS, UMR 5218, IMS, F-33400 Talence, France

Resume : Self-assembly of organic monolayers (SAM) on solid surfaces is a common technique to modify surface and interfacial properties and are used to alter the wettability, conductivity and biocompatibility of the surface. In this study, we show the self-assembly of perfluorocarbons , free base and metal based fluorinated porphyrins on methylammoniumleadiodide (CH3NH3PbI3) perovskite thin film and demonstrate the interaction of perovskite surface with fluorine by X-ray photoelectron spectroscopy (XPS), Kelvin probe microscopy (KPM) and polarization-modulated infrared reflection absorption spectroscopy (PMIRRAS) measurements. From PMIRRAS measurements, it emerges that weak non-covalent halogen bonding between fluorine from the perfluorocarbon or perfluorinated porphyrin and the perovskite are the driving forces for the formation of SAM on perovskite surface. To the best of our knowledge this is the first report of PMIRRAS measurement on perovskite surface to prove halogen bonding and formation of monolayer. Though the CH3NH3PbI3 perovskite thin film have enormous potential in the area of photovoltaic research, but the perovskite surface is very prone to moisture absorbance which drastically reduces the stability of the device by decomposition of the CH3NH3PbI3 crystal structure to methylamine (CH3NH2). Fluorocarbons are well known for their water repelling properties and generate a strong interfacial dipole moment due to the high electronegativity of fluorine. Thus, the presence of hydrophobic fluorine group on the perovskite surface may improve the stability and efficiency of HOIP-based devices by altering the work function.

Authors : Nur Fadilah Jamaludin, Natalia Yantara, Yan Fong Ng, Annalisa Bruno, Bevita K. Chandran, Xin Yu Chin, Krishnamoorthy Thirumal, Nripan Mathews, Cesare Socid and Subodh Mhaisalkar*
Affiliations : Nanyang Technological University

Resume : Identified as emerging light absorbers due to their plethora of unique optoelectronic properties, perovskites have also been touted as a promising candidate for light emission. However, despite the effortless transition of perovskites into the current organic light-emitting diodes (OLEDs), misalignment of energy levels at the hole transporting material (HTM) and perovskite interface limits the efficacy of interfacial charge transport. Herein, it is shown that by incorporating a small organic molecule, bathophenanthroline (BPhen), into the CH3NH3PbBr3 emitter via a solvent engineering technique, the energy band levels of the perovskite can be tailored and the energy mismatch at the HTM/perovskite interface can be ameliorated through the formation of a graded emitter layer and accompanying morphological improvements. With a BPhen concentration of 0.500 mg mL−1, more than ten-fold enhancement of device luminance and efficiency was achieved, thus demonstrating a facile and viable approach for fabricating high-performance perovskite light-emitting diodes (PeLEDs).

Authors : Ming-Hsien Li, Yu-Hsien Chiang, Po-Shen Shen, Yu-Syuan Yang, Peter Chen
Affiliations : Department of Photonics and Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, No. 1, University Road, Tainan 701, Taiwan

Resume : We will report two device architectures using inorganic selective contact materials for perovskite solar cells. The first one is a sandwiched configuration where perovskite is in contact with n-type and p-type oxide. No organic buffer layer is required to completed the device. The other one is a monolithic device where a thin (100nm) porous Au:NiOx counter electrode is formed on top of TiO2/Al2O3 mesoscopic scaffold. The perovskite is filled in as the last step to complete the device. A monolithic substrate with such architecture is robust and recyclable that the perovskite can be washed off and refilled. The stability performance will be presented. We believe that these device configurations have promising potential for commercializing cost-effective, large scale, and robust perovskite solar cells.

Authors : Claudiu Mortan, Michael Weber, Jochen Rank, Michael Wußler, Tim Hellmann, Ralph Dachauer, Chittaranjan Das, Kerstin Lakus-Wollny, Thomas Mayer, Wolfram Jaegermann
Affiliations : Department of Materials Science, Surface Science Group, TU Darmstadt, Darmstadt, 64287, Germany

Resume : The water solubility and toxicity of components in lead containing perovskite thin-film solar cells raise concerns over their implementation as feasible commercial products. Substitution of the lead (Pb) in the perovskite with another post-transition metal such as tin (Sn) could result in a wider acceptance. The best-known efficiency using CH3NH3SnI3 was published in 2014 by Noel, N.K., et al., who achieved a record PCE of 6,4% using the spin-coating technique [1]. We intend to build fully vacuum processed perovskite solar cells. In our labs we could produce and analyse lead (Pb) based perovskite solar cells using Glass/FTO/c-TiO2/m-TiO2/CH3NH3PbI3/spiroMeOTAD/Au by means of spin coating with a highest recorded efficiency of 15,6%. Working on the transition to lead-free perovskite solar cells, a Vacuum Flash Evaporation prototype has been built and tested. Analysis methods include XPS, XRD, SEM, PL, microscopy, solar simulator, etc. As upcoming research, tuning the band gap of the material using mixtures of Bromide (Br-) and iodide (I-) in the perovskite and building working devices could be proven useful for constructing tandem solar cell devices. [1] Noel, N.K., et al., Lead-free organic?inorganic tin halide perovskites for photovoltaic applications. Energy & Environmental Science, 2014. 7(9): p.3061-3068

Authors : Ying Suet LAU, Furong ZHU* *Email:
Affiliations : Department of Physics, Hong Kong Baptist University, Hong Kong

Resume : The performance of perovskite light-emitting diodes (PeLEDs) has been substantially improved over the past few years. However, the related fundamental physics is still far from adequate. A comprehensive analysis of morphology and growth mechanism of the perovskite light-emitting layers, charge injection and suppression of trap density in cesium lead bromide (CsPbBr3)-based PeLEDs was carried out. A hybrid precursor of poly(ethylene oxide) (PEO) and cesium carbonate (Cs2CO3) was used in the formulation of CsPbBr3-PEO-Cs2CO3-based perovskite light-emitting layer. The results show that the use of PEO and Cs2CO3 precursors benefits the operation of the CsPbBr3-PEO-Cs2CO3-based green PeLEDs in the two ways: (1) the presence of PEO in the emitting layer suppresses both the trap density and non-radiative recombination-induced leakage current, realized through passivating the perovskite crystal boundary defects and decreasing CsPbBr3 crystal grain size; (2) the incorporation of Cs2CO3 helps to improve the hole-blocking and electron-transporting in the active layer. As a result, the CsPbBr3-PEO-Cs2CO3-based green PeLEDs with a maximum current efficiency of 1.18 cd/A were obtained, which is about 6 times higher than that of a CsPbBr3-based control PeLED (0.20 cd/A). The CsPbBr3-PEO-Cs2CO3-based all inorganic green PeLEDs also possess a maximum luminance of 10290 cd/m2.

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Interfaces in Perovskite Solar Cells : tba
Authors : Germà Garcia-Belmonte
Affiliations : Institute of Advanced Materials (INAM), Universitat Jaume I, 12006 Castelló, Spain

Resume : Hybrid lead halide perovskite-based solar cells have reached very large solar to electricity power conversion efficiencies. The most extensively studied has been CH3NH3PbI3 (MAPbI3) perovskite as absorber material, in combination with electron (TiO2) and hole (spiro-OMeTAD) selective contacts. The current density?voltage curves of perovskite solar cells (PSCs) are found to present a hysteresis-like distortion when the measurement is done by sweeping the applied voltage at different scan conditions. Hysteresis has raised many concerns about the feasibility and long-term stability of this kind of photovoltaic technology. Recent experimental work shows a connection between capacitive current and hysteresis behavior in hybrid lead halide perovskites.1 PSCs present a distinctive capacitive feature in the low-frequency wing of the spectra. A huge increase of capacitance, which grows with illumination and charge injection up to mF?cm?2 (under 1 sun light or 1.0?V), has been measured and connected to the hysteretic features and surface/interface phenomena.2 Also resistances determined by impedance spectroscopy can be easily interpreted in terms of known recombination and extraction mechanisms. All these capacitive/resistive features point to the occurrence of determinant electronic processes at the interfaces between hybrid perovskite and selective contacts governing the performance of PSCs.3,4 We show here an exhaustive survey and recent advances concerning operating electronic mechanisms in PSCs. The impedance spectroscopy response of high-efficiency solar cells based on pure CH3NH3PbI3 and mixed Cs0.1FA0.74MA0.13PbI2.48Br0.39 perovskites are compared in relation to recombination models. Also the role of interlayers such as 2D perovskite thin capping with AVA2PbI4 between TiO2 and MAPbI3, and/or Bl2PbI4 between MAPbI3 and spiro-OMeTAD is discussed. Similarly, CFMPIB variants included PEA2PbI4 as a thin coating at both interfaces. All these experiments allow progressing in a proper understanding of the prominent role of outer interfaces in the operation of perovskite solar cells. 1. Almora, O.; Zarazua, I.; Mas-Marza, E.; Mora-Sero, I.; Bisquert, J.; Garcia-Belmonte, G., Capacitive Dark Currents, Hysteresis, and Electrode Polarization in Lead Halide Perovskite Solar Cells. J. Phys. Chem. Lett. 2015, 6, 1645?1652. 2. Zarazua, I.; Bisquert, J.; Garcia-Belmonte, G. Light-Induced Space-Charge Accumulation Zone as Photovoltaic Mechanism in Perovskite Solar Cells. The Journal of Physical Chemistry Letters, 2016, 7, 525-528. 3. Zarazua, I.; Han, G.; Boix, P.P.; Mhaisalkar, S.G.; Fabregat-Santiago, F.; Mora-Seró, I.; Bisquert, J.; Garcia-Belmonte, G. Surface Recombination and Collection Efficiency in Perovskite Solar Cells from Impedance Analysis. The Journal of Physical Chemistry Letters, 2016, 7, 5105-5113. 4. Almora, O.; Cho, K.Taek; Aghazada, S.; Zimmermann, I.; Matt, G.J.; Brabec, C.J.; Nazeeruddin, M.Khaja; Garcia-Belmonte, G. Discerning recombination mechanisms and ideality factors through impedance analysis of high-efficiency perovskite solar cells. Nano Energy, 2018, 48, 63-72.

Authors : Tim Hellmann, Michael Wussler, Dr. Chittaranjan Das, Claudiu Mortan, Dr. Eric Mankel, Dr. Thomas Mayer, Prof. Dr. Wolfram Jaegermann
Affiliations : Department of Materials Science, Surface Science Group, TU Darmstadt, Darmstadt, 64287, Germany

Resume : Methylammonium-lead-triiodide (CH3NH3PbI3) is still the most used perovskite absorber material up to now. The standard setup uses TiO2 as a front contact for the extraction of the electrons and spiro-MeOTAD as a hole transport material on top of the perovskite. However, there is not much known about the origin of the solar cells photovoltage. Schulz et al. performed photoelectron spectroscopy measurements on the spiro-MeOTAD interface to determine the band alignment but did not measure any photovoltage. We deposited CH3NH3PbI3 on top of a Glass/FTO/c TiO2/mp-TiO2 setup by a spin-coating process. Our spin-coating process does usually result in perovskite films with average efficiencies of more than 10%. The sample was then transferred to our vacuum system and spiro-MeOTAD was deposited stepwise by thermal evaporation, followed by a stepwise sputter deposition of Au. Between every deposition step photoelectron spectroscopy measurements have been performed under exclusion of light as well as under illumination. The band alignments of the CH3NH3PbI3/spiro MeOTAD and the spiro-MeOTAD/Au interfaces have been determined. By comparing the dark and light measurements the presence of a photovoltage of up to 700 meV is shown. Surprisingly, the main contribution to the photovoltage seems to arise from the spiro-MeOTAD/Au contact. Furthermore, a diffusion of iodine towards the surface was observed during the sputter deposition of Au.

Authors : Małgorzata Wierzbowska
Affiliations : Institute of High Pressure Physics, Polish Academy of Sciences

Resume : The CH3NH3PbI3 crystal forms, in practice, a blend-like interface with the electron transporting layers of the solar cell devices. Thus, various surface orientations and defects at the interface are responsible for the hydrogen migration and dehydratation of the perovskite. This, in turn, is responsible for a lack of the structural stability. The physical and chemical background of this unwanted phenomenon is connected to the strong electron or hole doping and unsaturated surface bonds – unavoidable due to a large lattice mismatch of the two materials. Moreover, depending on the surface orientation and the interface defects, such as Zn (or Ga) or methylammonium cation vacancies, the trap states at the junction mght occur or not. The theoretical modeling, based on the DFT methods and beyond, will be presented. The simulations of the nitroden K-edge X-ray spectra and the EPR g-tensor allow to distinguish various interface atomic conformations and could be compared to the experiment.

Authors : Kyung-Geun Lim, Soyeong Ahn, Tae-Woo Lee
Affiliations : Korea Research Institute of Standards and Science (KRISS), 267 Gajeong-ro, Yuseong-Gu, Daejeon 34113, Republic of Korea. E-mail:

Resume : The dipole moment of interface materials has played the key role in efficient charge extraction in organic and hybrid perovskite solar cells, but the mechanisms of the interaction at the interface and of the resulting energy level alignment have not been well established. In this research, the decoupled dipole moments at the interface are investigated and clarified by using both the theoretical and experimental findings, with particular focus on dipolar interface materials and the consequent energy level alignment in organic and hybrid perovskite solar cells. The mechanisms of interface dipole moments in the interface layer are evaluated by using spontaneously and nonspontaneously aligned dipolar molecules, thereby the energy-level adjustment of the dipolar interface layer in the devices are elucidated. The diverse dipolar interface materials (e.g., self-assembled monolayers, conjugated or nonconjugated polymer, neutral molecules or electrolytes, zwitterion based molecules, electrolyte grafted copolymer) are introduced and classified according to their working mechanisms of decoupled dipole moments at the interface. We conclude that an efficient interface material and its particular treatment can be designed and developed by exploring the underlying mechanisms of the decoupled dipole moments.

Authors : Qiong Wang, and Antonio Abate*
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie, Kekuléstraße 5, 12489 Berlin, Germany

Resume : Perovskite solar cells can now easily get a high efficiency of over 20%, highly competitive to the photovoltaic performance of silicon solar cells, and thin film solar cells. The high open-circuit voltage (Voc) in perovskite solar cells is suspected to be origniated from the Fermi-level splitting in the bulk perovskite layer. Here we show that by fine tuning the interface chemistry of the electron selective contact, i.e. tin oxide, a Voc of 1265 mV can be achieved at a band gap of 1.62 eV. As far as we know, this is the record Voc ever reported in triple cation perovskite solar cells. We believe this work will help to further promote the Voc to its theoretical limit.

10:30 Coffee Break    
Degradation of Perovskite Solar Cells : Dipankar Das Sarma
Authors : G. Divitini, S. Cacovich, F. Utama Kosasih, C. Ducati
Affiliations : University of Cambridge, Department of Materials Science and Metallurgy, Cambridge CB3 0FS

Resume : Progress in the area of perovskite-based photovoltaics has been remarkable over the past few years, with a large community working on improving the performance of materials and devices, and in particular focusing on extending the stability of hybrid perovskites by controlling their chemistry and the fabrication processes. Studies of PSC degradation under electrical biasing and illumination, as well as heating, carried out in the transmission electron microscope, reveal how the composition and morphology of each layer within the cell evolve under different stimuli. Recently we have studied triple cation perovskite formulations, where high spatial resolution and sensitivity to changes in crystallography, morphology and composition, are essential in determining the properties of the active layers of the devices.

Authors : H. J. Jung 2, D. Kim 1, S. Kim 2, V. P. Dravid 2, Byungha Shin 1
Affiliations : 1 Dept. of Materials Science and Engineering, Korea Advanced Institute of Science and Technology 2 Dept. of Materials Science and Engineering, Northwestern University

Resume : Using in-situ electrical biasing transmission electron microscopy, we examined structural and chemical modification to p-i-n type methylammonium lead triiodide (MAPbI3) solar cells with a TiO2 electron transporting layer caused by electrical bias in the absence of other stimuli known to affect the physical integrity of MAPbI3 such as moisture, oxygen, light, and thermal stress. Electron energy loss spectroscopy measurements revealed that oxygen ions were released from the TiO2 and migrated into the MAPbI3 under forward bias. The injection of oxygen was accompanied by significant structural transformation; a single crystalline MAPbI3 grain became amorphous with the appearance of PbI2. Withdrawal of oxygen back to the TiO2, and some restoration of the crystallinity of the MAPbI3 was observed after the storage in dark under no bias. A subsequent application of reverse bias further removed more oxygen ions from the MAPbI3. Light current-voltage measurements of perovskite solar cells exhibited poorer performance after elongated forward biasing; recovery of the performance, though not complete, was achieved by subsequently applying negative bias. These results indicate negative impacts on the device performance caused by the oxygen migration to the MAPbI3 under forward bias. Our study identified a new degradation mechanism intrinsic to p-i-n MAPbI3 devices with TiO2.

Authors : C. Hartmann1, G. Sadoughi2, R. G. Wilks1,3, M. Favaro1, D. E. Starr1, E. J. Crumlin4, H. Snaith2, M. Bär1,3
Affiliations : 1Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin, Germany 2Department of Physics, Clarendon Laboratory, University of Oxford, Oxford, UK 3Energy Materials In-Situ Laboratory Berlin (EMIL), Helmholtz-Zentrum Berlin für Materialien und Energie GmbH 4Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

Resume : Hybrid organometallic perovskites are still inhibited by the instability of the absorber,1 which is sensitive to moisture/water and ultraviolet (UV) light.2 In order to move toward real life implementation of the technology an understanding of the underlying pathways leading to degradation is necessary to ultimately improve the stability of the device. Ambient pressure hard x-ray photoelectron spectroscopy (AP-HAXPES) measurements have been performed at the 9.3.1 beamline at the ALS3 to track the changes of the chemical structure of CH3NH3PbI(3-x)Clx perovskite, in-situ over time in environmental conditions. Under vacuum conditions, in the dark, the film is stable over time. Exposure to water vapor at 15 Torr leads to degradation of the perovskite according to Ref.2,4. We find PbI2 to be the main (non-volatile) degradation product that further decomposes under illumination (even) at low water pressure (high vacuum) to Pb0 and I2. In our contribution, we discuss in detail the changes of the chemical structure of CH3NH3PbI(3-x)Clx in the dark and under illumination and at different water vapor levels. We describe and deconvolve the partially overlapping and competing interactions of the perovskite material with UV light, water, and x-rays. 1T. Leijtens et al., Advanced Energy Materials 2015, 5(20):1500963. 2G. Niu et al., Journal of Materials Chemistry A 2015, 3:8970. 3S. Axnanda, Scientific Reports 2015, 5, 9788. 4H.-S. Kim et al., ChemSusChem 2016, 9(18):2528.

Authors : Azat F. Akbulatov (1), Lyubov A. Frolova (2,1), Sergey Luchkin (2), Moneim Ismail (2), Sergey A. Tsarev (2), Keith J. Stevenson (2), Vyacheslav M. Martynenko (1) and Pavel A. Troshin (2,1*)
Affiliations : (1) Institute for Problems of Chemical Physics of RAS, Semenov ave. 1, Chernogolovka, Moscow region, 142432, Russia. (2) Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Nobel st. 3, Moscow, 121205, Russian Federation

Resume : The emerging perovskite solar cells have demonstrated impressive power conversion efficiencies exceeding 22%, while their practical application is restricted mainly by poor operation stability. We have reported recently that hybrid MAPbX3 (X=I, Br, I+Br, I+Cl) perovskites undergo facile thermal and photochemical degradation even under anoxic conditions without exposure to oxygen and moisture, while their all-inorganic counterparts CsPbX3 proved to be significantly more stable [1]. Here we will discuss our the most recent results coming from a systematic study of the intrinsic stability of a broad range of materials represented by various lead-based perovskites as well as lead-free complex halides of tin, germanium, bismuth and antimony. The revealed pathways of thermal, photochemical and electrochemical degradation processes will be presented and a conclusion on the potential of different groups of materials for practical application in PV technology will be drawn [2-3]. 1. A. F. Akbulatov, K. J. Stevenson, P. A. Troshin et al., J. Phys. Chem. Lett. 2017, 8, 1211 2. S.Yu. Luchkin, P. A. Troshin, K. J. Stevenson et al., ACS App. Mater. Interfaces 2017, 9, 33478 3. A. F. Akbulatov, K. J. Stevenson, P. A. Troshin et al., Adv. Energ. Mater. 2017, 7, 1700476

12:30 Lunch Break    
Optoelectronic Properties of Perovskites : Sagar M Jain
Authors : Selina Olthof
Affiliations : University of Cologne

Resume : In recent years, the interest in hybrid organic - inorganic perovskites rose at a rapid pace due to their tremendous success in the field of photovoltaic; but other fields, like light emitting diodes, show great potential as well. In such devices, the function and performance depend crucially on the proper alignment of the energy level landscape throughout the device, i.e. allowing for efficient charge transport across the various interfaces. Here, an advantage of these novel semiconductors is that the electronic structure and band gap energy can be readily tuned by changing the compositions of the perovskite. In this talk, I will discuss recent findings regarding the variations in electronic structure of hybrid perovskites, covering all lead and tin based halide systems using a combined DFT and UV-/ inverse/ x-ray photoelectron spectroscopy study. Furthermore, with these surface sensitive techniques, the energetic alignment at interfaces between different layers can be probed in-situ by performing a stepwise film preparation. Looking at various bottom contacts I will show that chemical interactions, band bending, and interface dipole formation play an important role.

Authors : Stepan Demchyshyn 1, Serdar Saricifci 2, Markus Scharber 2, Siegfried Bauer 3, Martin Kaltenbrunner 1
Affiliations : 1) Soft Electronics Laboratory, LIT, Johannes Kepler University Linz, Altenbergerstr. 69, A-4040 Linz, Austria; 2) Linz Institute for Organic Solar Cells, Johannes Kepler University Linz, Altenbergerstr. 69, A-4040 Linz, Austria; 3) Soft Matter Physics, Johannes Kepler University Linz, Altenbergerstr. 69, A-4040 Linz, Austria

Resume : Halide perovskites are inexpensive and easily processable next generation semiconductors. We here demonstrate perovskite solid-state confinement in nanoporous oxide matrices as a general strategy to control the size of the nanocrystallites (<10 nm) in the strong quantum size effect region. Photoluminescence tuning between near infrared and ultraviolet is achieved by manipulating the size of perovskite crystals through confinement in nanoporous alumina (npAAO) or silicon (npSi) scaffolds [1]. Our novel method of nanocrystalline perovskites preparation within a porous oxide matrix results in device-relevant structure that requires no colloidal stabilization. Low-voltage LEDs with narrow, blue-shifted emission fabricated with perovskite nanocrystallites confined within npAAO thin films support the general concept for next-generation photonic devices. The template-controlled size of the perovskite crystals is quantified in npSi with microfocus high-energy X-ray depth profiling in transmission geometry, verifying the growth of perovskite nanocrystals throughout the entire thickness of the nanoporous films. We study in detail exciton recombination, exciton-phonon interactions and energy trap states in confined and bulk semiconductor films using low temperature photoluminescence spectroscopy down to 3.8 Kelvin. Further areas of application include photon detectors, (polarized) electroluminescent devices, single-photon sources and metasurfaces. Future developments will include increasing the efficiency of the LEDs, exploring their applications in flexible devices and in depth study of the fundamental properties of the confined structures. [1] S. Demchyshyn, J. Roemer, H. Groiss, H. Heilbrunner, C. Ulbricht, D. Apaydin, A. Böhm, U. Ruett, F. Bertram, G. Hesser, M. Scharber, N. S. Sariciftci, B. Nickel, S. Bauer, E. D. Głowacki and M. Kaltenbrunner, “Confining Metal-Halide Perovskites in Nanoporous Thin Films”, Science Advances 3 (8), e1700738 (2017).

Authors : Elizabeth S. Parrott, Thomas Green, Rebecca L. Milot, Michael B. Johnston, Henry J. Snaith, Laura M. Herz
Affiliations : University of Oxford, Department of Physics, Oxford, OX1 3PU, UK.

Resume : Mixed lead-tin perovskites are promising absorber materials for low band-gap bottom cells in all-perovskite tandem devices [1]. The band-gap and charge-carrier recombination dynamics, essential properties in optimizing materials for solar cells and other devices, are investigated for formamidinium mixed lead-tin triiodide (FAPb1-xSnxI3) as a function of metal composition and temperature. Phase transition temperatures are reported, and a parabolic band-gap bowing parameter is identified from optical absorption, which takes a different value in the room temperature and low temperature phase, suggesting that bowing can be controlled by structural changes. The electron-hole recombination dynamics change substantially with composition and the time-resolved photoluminescence can be split into a tin-rich regime exhibiting short mono-exponential decays similar to those observed in CH3NH3SnI3 [2], likely due to doping, and a lead-rich regime with longer stretched decays. At low charge-carrier densities, the dominant charge-carrier recombination mechanism is found to be non-radiative for all compositions at room temperature. This strongly suggests that efforts to increase lifetimes of tin-rich perovskites should focus not only on controlling doping densities but also on reducing non-radiative recombination via trap states. The results show the importance of structure and composition in controlling band-gap bowing and charge-carrier recombination mechanisms, paving the way to engineering higher efficiency low band-gap absorbers for all-perovskite tandem solar cells. References [1] G. E. Eperon, T. Leijtens, K. A. Bush, R. Prasanna, T. Green, D. P. Wang, Jacob Tse-Wei Mcmeekin, G. Volonakis, R. L. Milot, R. May, A. Palmstrom, D. J. Slotcavage, R. A. Belisle, J. B. Patel, E. S. Parrott, R. J. Sutton, W. Ma, F. Moghadam, B. Conings, A. Babayigit, H. Boyen, S. Bent, F. Giustino, L. M. Herz, M. B. Johnston, M. D. McGehee, H. J. Snaith, Science (2016), 364, 861. [2] E. S. Parrott, R. L. Milot, T. Stergiopoulos, H. J. Snaith, M. B. Johnston, L. M. Herz, J. Phys. Chem. Lett. (2016), 7, 1321.

Authors : Takashi Komesu (A), Xin Huang (A,B), Tula R. Paudel (A), Yaroslav B. Losovyj (C), Xin Zhang (A), Eike F. Schwier (D), Yohei Kojima (E), Mingtian Zheng (E), Hideaki Iwasawa (D), Kenya Shimada (D), Makhsud I. Saidaminov (F), Dong Shi (F), Ahmed L. Abdelhady (F), Osman M. Bakr (F), Shuai Dong (B), Evgeny Y. Tsymbal (A), and Peter A. Dowben (A)
Affiliations : A) Dept. of Phys. and Astron., University of Nebraska-Lincoln, U.S.A. B) Dept. of Phys., Southeast University, China C) Dept. of Chem., Indiana University, U.S.A. D) Hiroshima Synchrotron Radiation Center, Hiroshima University, Japan E) Graduate School of Science, Hiroshima University, Japan F) Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Saudi Arabia

Resume : Organic-inorganic perovskites have been heavily investigated as candidates for next generation photovoltaic cells. The reported efficiency of CH3NH3PbX3 (X = Cl, Br, I) based perovskite thin film solar cells has seen rapid improvements, yet few fundamental experimental studies of electronic structure have been performed on such materials. The electronic structure and band dispersion of methylammonium (MA = CH3NH3+) lead bromide, CH3NH3PbBr3, has been investigated through a combination of angle-resolved photoemission spectroscopy (ARPES) and inverse photoemission spectroscopy (IPES), as well as theoretical modeling based on density functional theory (DFT). The experimental band structures are consistent with DFT calculations. The results demonstrate the presence of a dispersing occupied band in MAPbBr3 that peaks at the point of the surface Brillouin zone (SBZ), with strong Pb spectral contributions. The results also indicate that the surface termination of the MAPbBr3 is the methylammonium bromide (MABr) layer, discussed in this presentation. We find our results support models that predict a heavier hole effective mass in the region of -0.23 to -0.26 me (me : the mass of a free electron), along the (SBZ center) to point of the SBZ edge. The surface appears to be n-type as a result of an excess of lead in the surface region.

Authors : Aniela Czudek 1 2, Katrin Hirselandt 1, Lukas Kegelmann 1, Amran Al Ashouri 1, Steve Albrecht 1, Eva Unger 1 3
Affiliations : 1 Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin, Germany; 2 Warsaw University of Technology, Plac Politechniki 1, 00661 Warsaw, Poland; 3 Lund University, Paradisgatan 2, 22100 Lund, Sweden;

Resume : Precise evaluation of perovskite solar cells' performance is impaired by transient current-voltage phenomena. These effects may cause a discrepancy between current-voltage measurements performed in different scan directions, commonly referred to as hysteresis. We here present a procedure to assess the steady-state performance as well as the characteristic transient response of perovskite solar cells based on a perturb & observe maximum power point tracking algorithm. In our dynamic maximum power point algorithm (dynaMPP), the transient current response dynamics upon a voltage perturbation around maximum power point is recorded. Transient time constants are determined from exponential fits, from which the minimum suitable delay time to perform IV-measurements in steady-state conditions can be determined. Furthermore, our procedure provides means to compare perovskite solar cells devices of different architecture types, composition, selective contacts and age in terms of their characteristic transient current-voltage response. The procedure will prove useful to be integrated into long-term stability testing of perovskite devices as characteristic transient times might change upon device degradation due to the formation of defects and properties at selective contacts.

15:30 Coffee Break    
Towards High Performance : Zhiping Wang
Authors : Daniel Prochowicz
Affiliations : Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

Resume : The recent discovery of hybrid organic-inorganic metal halide perovskites led to a renaissance of thin film photovoltaics.[1] The great diversity of hybrid perovskite compositions and preparation pathways makes them an excellent candidate for novel photovoltaic materials with unique combination of properties, the potential for low cost and easy processing along with relatively high power conversion efficiencies.[2] Crystallinity, density of defects and impurities are key factors for optoelectronic properties, and are also highly dependent on the materials formation processes for most inorganic semiconductors. Understanding this behaviour and the structure/property relationship is crucial for fundamental understanding of perovskite materials, and for extending their properties to other process-tolerant systems. In that context, the synthetic approach induced by mechanical forces has appeared as a new emerging methodology in materials science.[3] The mechanochemical reactions in solid state offer a significant advance by avoid the use of solvent, dramatically shortening synthesis times and simultaneously increasing the purity and amount of product. Herein, we present a facile mechanochemical route for the preparation of various hybrid perovskite particles for high-efficiency thin-film photovoltaics.[4] We also demonstrate that such approach applied for preparation of perovskite materials has advantage over a solution-based synthetic routes in terms of hysteresis and device performance.[5] In addition, mechanochemistry allows the facile synthesis of large quantities of polycrystalline materials that is particularly well-suited for solid-state NMR studies, which can provide direct information about cation dynamics and atomic level phase compositions.[6] These studies highlight the essential need for atomic-level characterization of photovoltaic perovskite materials and provide fundamental understanding of photovoltaic parameters in these systems and their superior stability. References [1] M. Grätzel, Nat. Mater. 2014, 13, 838; (b) N.-G. Park, Mater. Today 2015, 18, 65. [2] W. S. Yang, B.-W. Park, E. H. Jung, N. J. Jeon, Y. C. Kim, D. U. Lee, S. S. Shin, J. Seo, E. K. Kim, J. H. Noh, S. I. Seok, Science 2017, 356, 1376. [3] S. L. James et. al., Chem. Soc. Rev. 2012, 41, 413. [4] (a) D. Prochowicz, M. Franckevi?ius, A. M. Cie?lak, S. M. Zakeeruddin, M. Grätzel, J. Lewi?ski, J. Mater. Chem. A 2015, 3, 20772; (b) D. Prochowicz, P. Yadav, M. Saliba, M. Saski, S. M. Zakeeruddin, J. Lewi?ski, M. Grätzel, Sustain. Energy Fuels 2017, 1, 689. [5] (a) D. Prochowicz, P. Yadav, M. Saliba, M. Saski, S. Zakeeruddin, J. Lewinski, M. Grätzel, ACS Appl. Mater. Interfaces, 2017, 9, 28418; (b) D. Prochowicz, P. Yadav, M. Saliba, D. J. Kubicki, M.M. Tavakoli, S. M. Zakeeruddin, J. Lewi?ski, L. Emsley, M. Grätzel, Nano Energy, 2018, DOI:10.1016/j.nanoen.2018.05.010. [6] (a) D. J. Kubicki, D. Prochowicz, A. Hofstetter, S. M. Zakeeruddin, M. Grätzel, L. Emsley. J. Am. Chem. Soc. 2017, 139, 14173. (b) D. J. Kubicki, D. Prochowicz, A. Hofstetter, M. Saski, P. Yadav, D. Bi, N. Pellet, J. Lewinski, S. M. Zakeeruddin, M. Grätzel, L. Emsley. J. Am. Chem. Soc. 2018, 140, 3345.

Authors : Mi-Kyung Jeon, Hock Beng Lee and Jae-Wook Kang*
Affiliations : Graduate School of Flexible of Printed Electronics, Chonbuk National University, Jeonju, 54896 Republic of Korea

Resume : The variation of anti-solvent is the key factor in controlling the crystallinity and microstructural properties of perovskite films. In this study, we fabricated (FAPbI₃)₁-x(MAPbBr₃)x planar perovskite solar cells (PSCs) employing various anti-solvents, i.e. chlorobenzene, toluene, ethyl acetate and mixed anti-solvent (MAS) for the in-situ crystallization of perovskite film. The photovoltaic performances of PSCs are concisely studied with respect to the morphology and crystallinity changes of the perovskite films. Our findings demonstrated that different anti-solvents has led to different degrees of crystallinity and morphology in perovskite films. Particularly, MAS has been extremely effective in increasing nucleation density of perovskite crystal and suppressing crystal cracks. Among all of the devices, MAS treated PSC exhibited the highest PCE (17.3%) with negligible hysteresis, owing to improved optical absorption and lesser pin-holes in perovskite film. Additionally, MAS treated PSC also displayed remarkably improved air-stability. In summary, our work herein embodies a facile, low-temperature solution route to fabricate high performance PSCs using one-step preparation method.

Authors : Zhiliang Chen, Guang Yang, Xiaolu Zheng, Guojia Fang
Affiliations : Zhiliang Chen, School of physics and technology, Wuhan University; Guang Yang, School of physics and technology, Wuhan University; Xiaolu Zheng, School of physics and technology, Wuhan University; Guojia Fang, School of physics and technology, Wuhan University;

Resume : The carrier concentration of the electron-selective layer (ESL) and hole-selective layer can significantly affect the performance of organic-inorganic lead halide perovskite solar cells (PSCs). Herein, a facile yet effective two-step method, i.e., room-temperature colloidal synthesis and low-temperature removal of additive (thiourea), to control the carrier concentration of SnO2 quantum dot (QD) ESLs to achieve high-performance PSCs is developed. By optimizing the electron density of SnO2 QD ESLs, a champion stabilized power output of 20.32% for the planar PSCs using triple cation perovskite absorber and 19.73% for those using CH3NH3PbI3 absorber is achieved. The superior uniformity of low-temperature processed SnO2 QD ESLs also enables the fabrication of ≈19% efficiency PSCs with an aperture area of 1.0 cm2 and 16.97% efficiency flexible device. The results demonstrate the promise of carrier-concentration-controlled SnO2 QD ESLs for fabricating stable, efficient, reproducible, large-scale, and flexible planar PSCs.

Authors : Nur Fadilah Jamaludin, Benny Febriansyah, Yan Fong Ng, Natalia Yantara, Annalisa Bruno, Nripan Mathews, Cesare Soci, Subodh Mhaisalkar
Affiliations : Nanyang Technological University

Resume : Research into perovskite-based light emitting diodes (PeLEDs) has been gaining momentum since early reports of its photoluminescence properties. However, despite its great potential as an emerging emitter material, its commercialization is still hampered by poor ambient and operational stability. Efforts to circumvent this have been primarily focused on the use of lower dimensional perovskites; which offer advantages such as ambient and thermal stability, high exciton binding energy and photoluminescence quantum yield. By amalgamating low dimensional (2D) perovskite with bulk (3D) perovskite to yield a quasi-dimensional variant, it is intended that the advantages of the former and latter can be leveraged upon for the fabrication of highly efficient Pe-LEDs. Here, phenyl ethyl ammonium, a common 2D templating agent, and two other similarly designed di-cationic molecules are incorporated into bulk 3D perovskite to correlate the effect of octahedra distortion on resultant perovskite properties. The increased defect density stemming from higher degree of octahedra distortion is shown to not only be detrimental to optical and electronic properties of the perovskite but also the performance of fabricated devices. This work paves the way for the rationalization of suitable 2D cationic species for enhancement of overall PeLED performance.

Authors : Paul Fassl1,2, Qing Sun1,2, Vincent Lami1,2, Alexandra Bausch1,2, Zhiping Wang3, Henry J. Snaith3 and Yana Vaynzof1,2
Affiliations : 1 Kirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany 2 Centre for Advanced Materials, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 225, 69120 Heidelberg, Germany 3 Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX13PU, UK

Resume : The field of lead halide perovskite materials and devices has attracted an incredible amount of interest from the scientific community in the last five years. While remarkable properties and device efficiencies have been demonstrated, staggering inconsisten-cies between different reports as well as an astoundingly wide distribution of device performance parameters have become routine in literature. Recently, we discovered that minute and quite possibly unintentional variations of the process of perovskite layer fabrication have a profound effect on the properties of per-ovskite materials as well as the performance and stability of perovskite photovoltaic de-vices. Specifically, we found that properties like surface composition and energetics, crystallinity, emission efficiency and energetic disorder are all exceptionally sensitive to these variations. As a result, the photovoltaic devices exhibit a broad distribution of power conversion efficiencies (~ 3%) and device stability (55% difference w.r.t initial performance). Interestingly, we observe that these fractional variations do not affect bulk properties such as absorption and morphology and so are not easily recognized by researchers in the field.[1] Additionally, we found that variations in performance of solar cells fabricated under identical conditions on a single substrate are related to the surface properties of the perovskite layer. By means of ultraviolet photoemission spectroscopy (UPS) we demonstrate that large scale inhomogeneities in the electronic structure of individual samples directly determine the variations in their photovoltaic performance.[2] [1] P. Fassl, V. Lami, A. Bausch, Z. Wang, H. J. Snaith and Y. Vaynzof, submitted [2] Q. Sun, P. Fassl and Y. Vaynzof, submitted

17:30 Coffee Break    
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ALD and Other Methods : Karsten Henkel
Authors : Mariadriana Creatore
Affiliations : Eindhoven University of Technology, Eindhoven, the Netherlands

Resume : Plasma-assisted ALD amorphous has been adopted in MeNH3PbI3 perovskite solar cells in a mesoscopic configuration, with the purpose of suppressing charge recombination processes at the ITO/ mesoscopic scaffold/perovskite interface. The superior performance of 10 nm thick ALD TiO2 layers (i.e. up to 16% cell efficiency under 1000/m2 illumination and 24% under indoor illumination) with respect to conventionally adopted spray pyrolysis TiO2, is explained by a lower reverse dark current measured for ALD TiO2. This result points out the superior blocking character of the ALD TiO2 layer toward electron-hole recombination. Furthermore, since ALD TiO2 is carried out at temperatures below 150C, flexible perovskite solar cells built on PET/ITO substrates are tested, exhibiting a conversion efficiency of 10.8% under indoor illumination, comparable to the performance of flexible dye-sensitized solar cells and exceeding the one of flexible a-Si:H solar cells. The same ALD TiO2 layer necessitates a F-based plasma post-treatment in order to serve as electron transport layer in planar n-i-p MeNH3PbI3 solar cells. Doping the TiO2 surface with F improves the energy band alignment between TiO2 and the absorber, according to UPS analysis, as well as favor a better mechanical adhesion at the interface. In the second case study, we address the role of 10 cycles of ALD Al2O3 deposited directly on top of MeNH3PbI3-xClx perovskite, effective in delivering a superior cell performance with 18% efficiency (compared to 15% of the Al2O3-free cell) and long-term stability. Motivated by the latter results, the present contribution focuses also on the chemical modifications which the hybrid perovskite undergoes upon growth of ALD Al2O3 on top. Specifically, we couple in situ infrared spectroscopy studies during film growth, together with XPS analysis of the ALD Al2O3/perovskite interface. This contribution ends by discussing the challenges yet to be met by ALD processing directly on the perovskite absorbers.

Authors : Dieter Schmeißer1, Malgorzata Kot1, Lukas Kegelmann2, Nataliya Tsud3
Affiliations : 1Brandenburg University of Technology Cottbus–Senftenberg, Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany; 2Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstraße 5, 12489 Berlin, Germany; 3Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic

Resume : CH3NH3PbI3 films show an increase in long-term stability and a protection against ambient conditions upon deposition of atomic layer deposited films of Al2O3 at room temperature [1,2]. In this work, the interaction of such Al2O3 (about one complete layer thick) film with the CH3NH3PbI3 substrate is investigated using the photoemission spectroscopy offered at the MSB beamline [3] at the Elettra Synchrotron in Trieste (Italy). In particular, the Pb 4f and I 3d core levels, and the valence band states (Pb5d, O2p), as well as the O1s X-ray absorption spectra (XAS) are characterized. An excitonic resonance in the O1s XAS spectrum and pronounced variations in the I3d/Pb4f ratio have been found. In addition, a Cooper minimum (CM) in the intensities of the O2p and Pb5d states is observed by varying the incident photon energy. The CM can be explained the formation of iodine and of methyl-ammonium vacancies and a charge donation from the Al atom. It creates a Pb-derived symmetry in the O2p valence states of Al2O3 and also explains the observed reduced photoionization cross section for the I3d signals. [1] M. Kot et al., ChemSusChem 9 (2016) 3401. [2] M. Kot et al., Nucl. Instrum. Methods Phys. Res. B 411 (2017) 49. [3] R. Vasina et al., Nucl. Instrum. Meth. A 467(2001) 561.

Authors : Sinclair Ratnasingham12, Martyn McLachlan1, Joe Briscoe2, Russell Binions2†,
Affiliations : 1 Department of Chemistry and Centre for Plastic Electronics, Imperial College London, SW7 2AZ, UK (; 2 School of Engineering and Materials Science and Materials Research Institute, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom

Resume : Hybrid organic-inorganic metal halide perovskite research has progressed rapidly, with photovoltaic devices reaching over 20% efficiency [1]. However, scalable production of these devices is an ongoing challenge. In this study we demonstrate the growth of methylammonium lead triiodide (MAPI) films via aerosol assisted chemical vapour deposition (AACVD). This is a scalable deposition process, working at atmospheric pressure, relatively low temperatures and requiring less complex equipment than conventional CVD, thus is able to produce large areas of material at low cost.2 The films were deposited by sequentially passing aerosolized precursor solvent solutions into a reactor containing a heated substrate. This process was then repeated to form film of appropriate thicknesses. It is shown that use of sequential deposition leads to high-quality, compact and smooth MAPI films. XRD measurements confirm the composition as MAPI. UV/vis absorbance measurements further validated the film composition, with Tauc plots giving an optical bandgap value of ~ 1.54 eV. SEM imaging revealed a film with large grains (2-10 µm), with film thicknesses ranging from 500-1500 nm. These films were then used to fabricate working photovoltaic devices in the n-i-p structure, a first for films made via AACVD. [1] M. Saliba, M. Grätzel Energy Environ. Sci. 1 (2016) 1989-1997 [2] M.Warwick, R. Binions Solmat (2016) 686-694

Authors : Carlo A.R. Perini, Annamaria Petrozza, Mario Caironi
Affiliations : Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, via G. Pascoli 70/3, 20133, Milan, Italy; Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy.

Resume : Metal halide perovskites are very promising for the realization of high performance, solution processed photodetectors, paving the way to cost-effective manufacturing of optoelectronics systems. However, most of the high-speed, high-detectivity perovskite photodiodes reported so far include evaporated interlayers in the device stack in order to limit dark currents. Here we adopt solution processed metal oxides as n-type charge selective interlayer, within a fully solution processed stack comprising a polymer p-type interlayer and a metal halide perovskite photoactive layer. As a result, dark current values are limited to 1.4 x 10^-7 A cm^-2 at -1 V, and responsivities exceeds 0.1 A W^-1 in the visible range. At the same time, the good conductivity of metal oxides allows for high operational speeds, providing decay times as low as 100 ns, an order of magnitude lower than what typically achieved with solution processed organic interlayers. Such responses corresponds to a -3 dB bandwidth of 3.5 MHz. Device stability is also enhanced thanks to the introduction of the metal oxide layer, with promising shelf life of devices for up to 80 days.

Authors : Azimatu Seidu, Lauri Himanen, Jingrui Li, Patrick Rinke
Affiliations : Department of Applied Physics, Aalto University P. O. Box 11100, FI-00076 Aalto, Finland

Resume : Recently, hybrid perovskite photovoltaics (HPPVs) have achieved conversion efficiencies of 22 % and have revived the search for clean, affordable and efficient energy. However, the practical realization of this hope is pending for several reasons. One of them is the stability of the photo-absorbing hybrid perovskites (HPs), which currently degrade rapidly when exposed to moisture [1]. Thus, the search is underway for a coating material to protect HPs. A proper coating should be thin to ensure minimum energy loss within the coating-perovskites interface. It should have a wide band gap in order to serve as a good window material and most importantly, be resistant to water. In this study, we consider a series of methylammonium (MA) metal (B=Pb or Sn) halide (X=I, Br or Cl) perovskites (MABX3) and their CsBX3 analogs. To select possible protective-coating candidates, we filtered the large Aflow [2] database for metal oxides and nitrides according to several criteria: wide band gap (> 3 eV), negligible reactivity with water, and minimal strain at the coating-perovskite interfaces. Our database screening results in several combinations of coating materials and perovskites substrates with strain < 5 %, for example, NiO at the 2 X 2 surface of MASnBr3 (strain 1.0%) and at the 2√2 X 2√2 surface of CsPbI3 (strain -1.6%). ZrO2 and GaN at 2 X 2 surface of MAPbI3 (strain -0.7% and 0.8%) respectively. For these candidate complexes, we further model their interface geometries and electronic structures using density-functional theory (DFT). This database-driven study and the following DFT modeling has the potential improve to the efficiency of HP materials and serve as a starting point in the search of novel device materials for emergent HPPV technologies. Keywords hybrid, perovskites, resistant, degrade Reference [1] M. A. Green, A. Ho-Baille, and H. J Snaith, Nature Photon. 8, 506(2014). [2] R. H. Taylor, F. Rose, C. Tohler, O. Levy, K. Yang, M. B. Nardelli, and S. Curtarolo, Computational Materials Science 93, 178 (2014).

15:30 Coffee Break    
Ferroelectricity and Charge Extraction : Daniel Prochowicz
Authors : Ioannis Deretzis, Antonino La Magna
Affiliations : CNR-IMM, Catania, Italy

Resume : Methylammonium lead tri-iodide (MAPbI3) is a polymorphic material with a remarkable potential for solar energy conversion. It is characterized by two temperature-induced phase transitions at 165 K and 327 K, accompanied by an orthorhombic-to-tetragonal and a tetragonal-to-cubic lattice modification, respectively. Understanding the origins of these transitions as well as their structural implications could be important for the technological optimization of this material. Here, we use ab initio molecular dynamics to study the phase changes of MAPbI3. We argue that the orthorhombic-to-tetragonal transition is characterized by an antiferroelectric to ferroelectric ordering, through the partial rearrangement of the organic cations that locally relaxes the stress arising from the thermal movement of atoms [1,2]. Besides, we propose a macroscopic model for the tetragonal phase that consists of rotated noncentrosymmetric domains where the MA ions are quasi-two-dimensionally confined around the a-b crystallographic plane. We finally show that the gradual disordering of the MA ions at higher temperatures triggers the tetragonal-to-cubic transition, resulting in a loss of the ferroelectric characteristics. [1] I. Deretzis, B.N. Di Mauro, A. Alberti, G. Pellegrino, E. Smecca, A. La Magna, Sci. Rep. 6, 24443 (2016) [2] I. Deretzis, A. La Magna, Nanoscale 9, 5896-5903 (2017)

Authors : Holger Röhm(1), Tobias Leonhard(1,2), Michael J. Hoffmann(2,3), Alexander Colsmann(1,2)
Affiliations : 1 Light Technology Institute, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany. 2 Material Research Center for Energy Systems, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany. 3 Institute for Applied Materials – Ceramic Materials and Technologies, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany.

Resume : Within five years, methylammonium lead iodide (MAPbI3) solar cells have quickly reached remarkable power conversion efficiencies rivaling those of established technologies. However, arguably, the toxic and water-soluble lead compound may be an obstacle on their way to market. The quest for alternative, non-toxic photo harvesters is partly hampered by a lack of fundamental understanding of the crystal grain’s characteristics and energy conversion mechanisms. As part of this process, the scientific community controversially discusses the importance of ferroic properties for the exceptional performance of MAPbI3 light-harvesting layers, including claims of non-ferroelectricity, anti-ferroelectricity, ferroelectricity and ferroelasticity. Simulations have predicted ferroelectricity in MAPbI3 with alternating polarized domains ruling the charge carrier transport [1]. Understanding the crystallographic cause and the effects of the crystal’s ferroelectricity would therefore provide helpful guidance for the quest to find non-toxic MAPbI3 replacements. We explore the ferroic properties of methylammonium lead iodide perovskite solar cells by piezoresponse force microscopy (PFM) [2][3]. In vertical and horizontal PFM imaging, we find 90 nm wide ferroelectric domains of alternating polarization. High-resolution photo-conductive atomic force micrographs under illumination also show alternating charge carrier extraction patterns which we attribute to the local vertical polarization components within the ferroelectric domains. We apply these techniques to investigate formation of polarized domains during thermal treatment and study their influence on the performance of perovskite solar cells. Annealing steps, commonly only viewed as a means of crystal growth and precursor conversion, prove to directly influence the formation, shape and polarization direction of ferroelectric domains in perovskite thin films. References: [1] D. Rossi, A. Pecchia, M. Auf der Maur, T. Leonhard, H. Röhm, M. J. Hoffmann, A. Colsmann, A. D. Carlo, Nano En. (2018). [2] H. Röhm, T. Leonhard, M.J. Hoffmann, A. Colsmann, Energy Environ. Sci. (2017). [3] T. Leonhard, A. Schulz, H. Röhm, S. Wagner, F. Altermann, W. Rheinheimer, M.J. Hoffmann, A. Colsmann, submitted.

Authors : Michiel L. Petrus, Kelly Schutt, Maximilian T. Sirtl, Eline M. Hutter, Anna C. Closs, James M. Ball, Johan C. Bijleveld, Annamaria Petrozza, Thomas Bein, Theo J. Dingemans, Tom J. Savenije, Henry Snaith, and Pablo Docampo
Affiliations : Michiel L. Petrus; Maximilian T.Sirtl; Anna C. Closs; Thomas Bein: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) Butenandtstr. 11, 81377 Munich, Germany; Kelly Schutt: Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom; Eline M. Hutter; Tom J. Savenije: Department of Chemical Engineering, Delft University of Technology, van der Maasweg 9, 2629 HZ Delft, The Netherlands; James M. Ball; Annamaria Petrozza: Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, via, Giovanni Pascoli 70/3, 20133, Milan, Italy; Johan C. Bijleveld: Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands; Theo J. Dingemans: Department of Applied Sciences, University of North Carolina, 1112 Murray Hall Chapel Hill, NC 27599-3216, USA; Pablo Docampo: Newcastle University, School of Electrical and Electronic Engineering, NE1 7RU Newcastle upon Tyne, UK;

Resume : Hybrid organic/inorganic perovskite solar cells employ hole-transporting materials of which Spiro-OMeTAD is the state-of-the-art material. However, this HTM is synthesized via cross-coupling reactions comprising Pd catalysts, resulting in extensive purification and high cost. Here, we introduce a new HTM (EDOT-Amide-TPA), in which a functional amide-based backbone is employed. This allows us to synthesize the molecule via simple condensation chemistry which results in a reduction of the synthesis cost, estimated to 5 $/g. When employed as an HTM, this material shows stabilized power conversion efficiencies above 20% and reproducibly outperforms Spiro-OMeTAD in direct comparison. This is linked to a faster hole-injection into the HTM-layer, which is determined by time-resolved microwave-conductivity measurements. Moreover, the devices exhibit an increased operational lifetime which we ascribe to the coordination of the amide bonds to Li-ions of the additive LiTFSI. This possibly limits the migration of Li-additives from the HTM to the perovskite layer. The outstanding charge carrier properties of our amide based HTM compared to fully conjugated molecules show that a complete conjugation of the HTM is not essential to achieve good charge carrier properties. Our EDOT-Amide-TPA outperforms Spiro-OMeTAD in stability and performance at a fraction of the cost, providing a new set of design strategies for new, low-cost HTMs.

Authors : Yueli Liu, Qiao Chen, Xizhu Zhao, Keqiang Chen, Wen Chen
Affiliations : State Key Laboratory of Silicate Materials for Architectures, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, P. R. China

Resume : The organic-inorganic hybrid perovskite solar cells have attracted tremendous attention of researchers all over the world [1-2]. However, the traditional hole transport materials (HTMs) of spiro-OMeTAD is costly [3]. It is critical to exploit an efficient and low-cost HTM in perovskite solar cells (PSCs). In this study, a p-type Cu12Sb4S13 quantum dots (QDs) are synthesized by a hot-injection method, which are applied as an efficient and low-cost inorganic hole transport layer in planar PSCs. On account of quantum confinement effect [4], the bandgap of QDs varies with different sizes of QDs. UPS measurements are taken to characterize the VB positions of QDs to optimize the size of QDs for the good charge transfer. IPCE spectrum indicates that the absorption of Cu12Sb4S13 QDs-based device is slightly higher than that of spiro-based one during 300-670 nm. EIS curves and the steady-state PL spectra demonstrate the fast hole extraction and reduced charge recombination at the perovskite/Au interface than that of the spiro-based devices. Eventually, a PCE of 8.73% is obtained under 100 mWcm−2 with a remarkably outstanding Jsc value of 22.29 mA cm−2. In summary, Cu12Sb4S13 QDs present the predominant hole transfer properties with a higher Jsc than the traditional spiro-OMeTAD, which provides a bright prospect for the future development of PSCs. References (1) Stranks S D, Eperon G E, Grancini G, et al. Science, 2013, 342(6156), 341-344. (2) Yang W S, Park B W, Jung E H, et al. Science, 2017, 356(6345), 1376-1379. (3) Lv M, Zhu J, Huang Y, et al. ACS Applied Materials & Interfaces, 2015, 7(31), 17482-17488. (4) Chen K, Zhou J, Chen W, et al. Particle & Particle Systems Characterization, 2015, 32(11), 999-1005.

Authors : Artiom Magomedov (a), Ernestas Kasparavičius (a), Amran Al-Ashouri (b), Sanghyun Paek (c), Vygintas Jankauskas (d), Mohammad Khaja Nazeeruddin (c), Steve Albrecht (b), Tadas Malinauskas (a), Vytautas Getautis (a)
Affiliations : (a) Department of Organic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, Kaunas 50254, Lithuania; (b) Institute for Silicon Photovoltaics, Helmholtz-Zentrum Berlin, Young Investigator Group for Perovskite Tandem Solar Cells, Kekuléstr. 5, Berlin, D-12489, Germany; (c) Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne, CH-1951 Sion, Switzerland; (d) Department of Solid State Electronics, Vilnius University, Sauletekio 9 III k., 10222 Vilnius, Lithuania

Resume : Carbazole heterocycle is a robust and cheap building block, which can be easily functionalized to achieve desired properties. In our work we are using carbazole as a starting material for the synthesis of the hole transporting materials (HTMs) for perovskite solar cells (PSCs). π-conjugated system of the carbazole can be expanded via bromination and subsequent functionalization with aromatic amines. Furthermore, hydrogen at the 9-th position can be used for the simple formation of the branched structures, or for introduction of other functionalities. First, series of branched carbazole-based HTMs was synthesized and tested for the performance in the PSCs, giving close to 19% power conversion efficiencies (PCE). Due to the simplicity of the synthesis, one of the HTMs (V886) was commercialized. V886 was further used to address the question of the intrinsic long-term instability of the doped HTMs. It was shown, that tert-butylpyridine can react with oxidized radical-cation HTM species, and pyridinated product was found in aged PSCs by means of MS analysis. This reaction was confirmed for other HTMs, that are used with dopants. Finally, substituted carbazole, functionalized with phosphonic acid group, was used for the self-assembled monolayer formation on ITO substrate, and was successfully integrated into inverted PSCs, giving close to 18% PCE. This new concept can be used as an alternative to the spin-coated HTM layers. Further development of this concept is currently on-going.

Authors : Hong Duc Pham (1), Jinhyun Kim (2), Sergei Manzhos (3), Krishna Feron (4, 5), James R. Durrant (2, 6), Sagar Motilal Jain (6), Prashant Sonar (1)*
Affiliations : (1) Institute of Future Environment and School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology (QUT); 2 George Street, Brisbane, QLD-4001, Australia; (2) Department of Chemistry and Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom; (3) Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore; (4) Centre for Organic Electronics, University of Newcastle, Callaghan, NSW 2308, Australia; (5) CSIRO Energy Centre, NSW-2304, Australia; (6) SPECIFIC, College of Engineering, Swansea University Bay Campus, Fabian Way, SA1 8EN Swansea, United Kingdom.

Resume : Up to date, perovskite solar cells (PSCs) have attracted lots of attention from the research community in the world because its power conversion efficiency (PCE) increased quickly from 3.8% to 22.7% within last seven years. In spite of achieving the world record PCE rapidly, the commercialization of PSCs still remains challenging due to its high production cost and less stability. The main reason is the intensive use of 2,2’,7,7’-tetrakis(N,N’-di-pmethoxyphenylamino)-9,9’-spirbiuorene (Spiro-OMeTAD) as standard hole transporting material (HTM). Although Spiro-OMeTAD based devices achieved a remarkable performance of 21.1%, there are still some main shortcomings of Spiro-OMeTAD, including high cost and multistep synthesis. Extraordinarily, Spiro-OMeTAD requires additives, which enhance the performance of the device, however, at the cost of stability. These bottlenecks can hamper the progress of low cost and large area flexible PSCs. In this work, we introduce three novel simple cost efficient solution processable small molecular HTMs, namely TPA-QA-TPA, ACE-QA-ACE and DPA-QA-DPA, using triphenylamine (TPA), acenaphthylene (ACE) and diphenylamine (DPA) as end-capping groups with quinacridone (QA) dye as the central core. These HTMs were fabricated in mesoscopic TiO2/CH3NH3PbI3/HTM solid-state PSCs without additives. Under 1 sun condition, the devices achieve the maximum efficiency of 17% for ACE-QA-ACE, 12% for DPA-QA-DPA and 6% for TPA-QA-TPA. First time we have used QA dye for making such non-doped HTMs for high performance Perovskite solar cells. Meanwhile, the reference device with doped Spiro-OMeTAD as HTM showed a PCE of 18%. Most importantly, the unencapsulated devices based on these novel pristine HTMs show impressive stability in comparison with the reference devices. These linear symmetrical HTMs pave the way for new classes of organic hole transporting materials for large area applications of printed PSCs.

17:30 Coffee Break    
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Doping, Defects and Traps : Selina Olthof
Authors : Juan-Pablo Correa-Baena
Affiliations : MIT

Resume : Perovskite solar cells promise to yield efficiencies beyond 30% by further improving the quality of the materials and devices. Electronic defect passivation, and suppression of detrimental charge-carrier recombination at the different device interfaces has been used as a strategy to achieve high performance perovskite solar cells. In this presentation, I will discuss the role of electronic defects and how these can be passivated to improve charge-carrier lifetimes and achieve high open-circuit voltages. I will discuss the characterization of 2D and 3D defects, such as grain boundaries, crystal surface defects, and precipitate formation within the films, by synchrotron-based techniques. The importance of interfaces and their contribution to detrimental recombination will also be discussed. As a result of my contribution to better understanding 2D and 3D defects, the perovskite solar cell field has been able to improve device performance. Albeit the rapid improvements in performance, there is still room for tailoring charge-carrier recombination in the perovskite, and at the interfaces within the device, to push these solar cells beyond the current state-of-the-art.

Authors : Nga Phung, Antonio Abate
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany

Resume : Halide perovskites are extraordinary photovoltaic materials that enabled to prepare solar cells exciding 22% power conversion efficiency [1]. Incorporating small amounts of foreign ions into the mix of precursors used to prepare the perovskite film is a well-known strategy to improve device performance and stability. For example, monovalent cations such as cesium, rubidium, and potassium are particularly effective to boost efficiency in state-of-the-art devices [2]. More recently, divalent and trivalent cations are attracting growing attention. For example, devices made from perovskite film prepared from precursor solutions comprising a small amount of strontium achieved a step improvement in the open circuit voltage [5]. While this approach of adding foreign ions into the mix of precursors may resemble classical doping of inorganic semiconductors, it seems to have a completely different working mechanism that is peculiar to halide perovskites. In this work, we explore the ionic doping mechanism of halide. We use advanced characterization techniques based on synchrotron measurements to understand the impact of foreign ions on the material. Then, we prepare perovskite solar cells to prove the mechanism in state-of-the-art devices. References [1] National Renewable Energy Laboratory, Best Research-Cell Efficiencies chart; [2] Saliba, M., et al., Science (2016), 354.6309, p. 206-209. [3] Abdi-Jalebi, M., et al., Nature, (2018), 555.7697, p. 497.. [4] Li, Z., et al., Energy & Environmental Science, (2017), 10.5, p.1234-1242.A. [5] Caprioglio, P., et al., Poster session presented at the PSCO (2017).

Authors : P.C. Harikesh, Bo Wu, Biplab Ghosh, Rohit Abraham John, Stener Lie, Krishnamoorthy Thirumal, Tze Chien Sum, Subodh Mhaisalkar, Nripan Mathews
Affiliations : Nanyang Technological University, Singapore

Resume : Creating defect tolerant lead-free halide perovskites is the major challenge for development of high-performance photovoltaics with non-toxic absorbers. Few compounds of Sn, Sb or Bi possess ns2 electronic configuration similar to lead, but their poor photovoltaic performances inspire us to evaluate other factors influencing defect tolerance properties. In this work, we adopt a combined theoretical and experimental approach to examine the effect of heavy element (Bismuth) addition and ion migration on the optoelectronic properties and defects in a novel 2D layered Antimony perovskite-(NH4)3Sb2I9. Gradual substitution of Sb with Bi results in controlled modulation of the band gap, carrier concentration and carrier types. We show for the first time, creating intrinsic p- and n-type materials by metal cation transmutation illustrating the relevance of the atomic mass of the metal cation in determining the defects and carrier properties of the halide perovskites. First principle calculations, AC hall measurements, thermal admittance spectroscopy and transient absorption measurements provide possible explanations for this observed behaviour. The pristine and transmutated materials exhibit a direct-indirect band gap with low trap densities and carrier lifetimes > 100 ns, the highest reported so far for any lead-free perovskite thin film. The study also demonstrates the possibility of electrical poling to induce switchable photovoltaic effect without additional electron and hole transport layers.

Authors : Svetlana Sirotinskaya 1), Christian Fettkenhauer 2), Yohei Yamamoto 3), Doru C. Lupascu 2), Roland Schmechel 1), Niels Benson 1)
Affiliations : 1) NST, University of Duisburg-Essen & CENIDE, Germany; 2) UDEMAT, University of Duisburg-Essen & CENIDE, Germany; 3) IMS, University of Tsukuba, Japan

Resume : One of the reasons for the unprecedented success of the perovskite development for photovoltaic applications, is the postulated beneficial trap physics in perovskite thin films. Yin et al. (APL, 104, 063903, 2014) described this in a recent theoretical publication for the MAPbI3 system. The research suggests, that point defects, as the major source for trap states in a perovskite crystal structure, mainly result in a density of states distribution, which is close to, or within the perovskite transport states, making them acceptable for solar cell operation. Further, experimental evidence by Edri et al. (Nano Lett., 14, 1000, 2014) indicates, that grain boundaries in MAPbI3 thin films also do not have a negative influence on the charge carrier transport. Here we present a detailed experimental study on the grain boundary and bulk traps in MAPbI3. Instead of using thin films, we used µm-size crystallites grown from solution as a model system. This has allowed us to conduct conclusive µ-PL, µ-XPS and Kelvin Probe grain boundary and bulk measurements, with which we could determine the trap depth (µ-PL) and the type of trap (µ-XPS), as the consequence of either substitutions, interstitials or voids in the crystal. Our findings will be confirmed using a Kelvin Probe investigation, as the relationship between Pb and I defines the position of the Fermi level. Using this study, we are able to experimentally confirm the mainly theoretical ideas of the trap physics in MAPbI3.

10:45 Coffee Break    
Engineering of Perovskite Solar Cells I : tba
Authors : Sagar M. Jain (a) , Jinhyun Park (b), Ilknur B. Pehlivan (c),Tomas Edvinsson (c), James Durrant (a,b)
Affiliations : (a) SPECIFIC, College of Engineering, Swansea University Bay Campus, Fabian Way, SA1 8EN Swansea, United Kingdom (b) Department of Chemistry and Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ, United Kingdom (c) Department of Engineering Sciences, Solid State Physics, Uppsala University, Box 534, SE 751 21 Uppsala, Sweden.

Resume : Perovskite semiconductors have shown great promise for making high-efficiency solar cells at low cost1. Since their first use in solar cells2. The power conversion efficiency (PCEs) of perovskite solar cells (PSCs) have speedily increased. The chemical structure can be tailored by combining various halides or utilizing different aliphatic ammonium ions, leading to tunable band gaps and charge transport properties.3 The certified power conversion efficiency has reached 22.3%4. Despite this rapid increased in power conversion efficiency of perovskite solar cells the maximum current is till upto 25.0 mA/cm2. The efficiency limit of perovskite cells without the angular restriction is about 31%, which approaches to Shockley-Queisser limit (33%) achieved by gallium arsenide (GaAs) cells.5 Moreover, theoretically the Shockley-Queisser limit could be possible to reached with only a 200 nm thick perovskite solar cell, through integrating a wavelength dependent angular restriction design with a textured light-trapping structure5 Alkylammonium lead (II) trihalide perovskite act as ambipolar charge transport characteristics and function well in solar cells with an inverted structure. For this device architecture, the perovskite forms a heterojunction with an organic charge transport material, such as fullerene (C60), {6,6}-phenyl C61-butyric acid methyl ester (PCBM) or conjugated polymer. The inverted structure (ITO/EEL/Perovskite/HEL/electrode) can be fabricated with reversed electrode polarity. In general, the inverted structure has better ambient stability and compatibility to all solution roll-to-roll application. Perovskite shows high intrinsic carrier mobility and high photon absorption 6 due to thickness of ~1000 nm there are severe charge recombination and losses7a,b,c Therefore, hampering the resultant current8. In this regard, delicate optical interlayer management is utilized to enhance the current. Inorganic interlayers due to their superior electronic properties and environmental stability compared to their organic counter parts and are considered very good candidates for interface engineering. The transition metal oxides with decent transparency across visible and infrared spectra have been widely proven to form good ohmic contact with absorbers due to their high conductivity and appropriate WF 9 (a),(b),(c) and (d) For an ideal Hole extraction layers (HELs), its HOMO level should align with the Ef,h of CH3NH3PbI3 layer while its LUMO level sits above the Ef,e of CH3NH3PbI3. In this direction we show that introduction of an additional buffer HTL of high work function metal oxide layer on NiOx decreases the concentration of deep-level defects. The interface engineering of this additional buffer layer helps collecting holes effectively hindering electrons this enable the fabrication of PSCs with power conversion efficiency of 21% under standard AM1.5 G conditions. with the highest ever recorded current of 27.8 mA/cm2 which is well matched with the current of 27.7 mA/cm2 obtained from EQE. References (1) (a) Nature 2013, 501,395. (b) Nature 2013, 499,316 (c) Sci. Rep. 2012,2,591 (d) Science 2013, 342,344. (e) Science 2013, 342,341 (f) Science 2015, 347,519 (g) Science 2015, 347,967 (2) J. AM. Chem. Soc. 2009, 131, 6050 (3) (a) J. H. Noh, S.H. Im, J. H. Heo, T.N. Mandal, S.I. Seok, Nano Lett., 2013, (b) M. I. Dar, N. Arora, P. Gao, S. Ahmad, M. Gratzel, M. K. Nazurridin, Nano Lett., 2014 (c) Y. Tidhar, E. Edri, H. Weissman, D. Zohar, G. Hodes, D. ?, J. Am. Chem. Soc., 2014 , (d) J.-W. Lee, D.-J. Seol, A.-N. Cho, N.-G. Park, Adv. Mater., 2014 (4) (a) Science 2014, 345,542 (b) Nature 2015, 517,476 (c) Science 2015, 348,1234 (d) Science 2015, 350, 944 (e) (5) Applied Physics Letters 2015, 106 (22): 221104 (6) Phys. Chem. Chem. Phys., 2015,17,11516-11520 (7) (a) J. AM. Chem. Soc. 2013, 135, 4656-4659 ; (b) Adv. Mater., 2013,25,6642-6671 ; (c) Nat. Photonics, 2013,7,825-833 (8) J. Phys. Chem. Lett., 2013,4,1821-1828 (9) (a) Nanoscale, vol. 8, no. 22, pp. 11403-11412, 2016 ; (b) Chemical Communications, vol. 52, no. 52, pp. 8099-8102, 2016 ; (c) Nanoscale, vol. 7, no. 21, pp. 9427-9432, 2015 ; (d) Advanced materials, vol. 25, no. 10, pp. 1504-1509, 2013 ; (e) ACS Nano 2016, 10, 3630-3636

Authors : Stepan Demchyshyn, Martin Kaltenbrunner
Affiliations : Soft Electronics Laboratory, LIT, Johannes Kepler University Linz, Altenbergerstr. 69, A-4040 Linz, Austria

Resume : Flexibility, compliance and weight will turn out to be key metrics for future electronic appliances and their power supplies. Emerging applications like solar powered aviation or wearable electronics require photovoltaic technologies that are highly efficient, light-weight, low-cost, and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. In this talk we introduce methods, materials and design strategies for ultrathin (3 µm), highly flexible perovskite solar cells with a record power-per-weight as high as 23 W/g [1]. To facilitate air stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. We show prolonged stable operation in ambient air of ultrathin non-encapsulated planar perovskite solar cells with gold, copper and aluminium electrodes. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles - from airplanes to quad-copters and weather balloons - for environmental and industrial monitoring, rescue and emergency response, and tactical security applications. In a hybrid architecture laminated atop pre-strained elastomers, such solar cells are highly stretchable and conformable. Tuning the band gap of perovskite semiconductors via quantum size effects is currently advancing optoelectronics. Here we introduce a general strategy of controlling shape and size of perovskite nanocrystallites (less than 10 nm) in domains that exhibit strong quantum size effects [2]. Without manipulation of halide stoichiometry, we achieve fine-tuning of band gap across a wide colour gamut from near infrared to ultraviolet through solid-state confinement in nanoporous alumina or silicon scaffolds. Confinement in npSi facilitates a ~50 nm hypsochromic shift from green to blue photoluminescence for caesium-bromide perovskite nanocrystals. By infiltrating electrically addressable npAAO templates, we fabricate perovskite nanorod light-emitting diodes achieving blue shifted narrow-band emission. Our device demonstrations corroborate band gap engineering through solid-state confinement as a powerful tool to precisely control the optoelectronic properties of perovskite nanocrystal emitters in next generation solution-derived photonic sources. [1] M. Kaltenbrunner, G. Adam, E.D. Głowacki, M. Drack, R. Schwödiauer, L. Leonat, D.H. Apaydin, H. Groiss, M.C. Scharber, M.S. White, N. S. Sariciftci, S. Bauer, “Flexible high power-per-weight perovskite solar cells with chromium oxide–metal contacts for improved stability in air”, Nature Materials 14, 1032-1039 (2015). [2] S. Demchyshyn, J. Roemer, H. Groiss, H. Heilbrunner, C. Ulbricht, D. Apaydin, A. Böhm, U. Ruett, F. Bertram, G. Hesser, M. Scharber, N. S. Sariciftci, B. Nickel, S. Bauer, E. D. Głowacki and M. Kaltenbrunner, “Confining Metal-Halide Perovskites in Nanoporous Thin Films”, Science Advances 3 (8), e1700738 (2017).

Authors : Yan Fong Ng, Nur Fadilah Jamaludin, Benny Febriansyah, Natalia Yantara, Subodh Mhaisalkar, Nripan Mathews
Affiliations : Nanyang Technological University, Singapore

Resume : The rapid progress of perovskite semiconductor research have not only seen record-breaking photovoltaic performances, but also established this material as a strong contender in the field of light emission. With the emergence of multidimensional perovskites where the incorporation of larger organic counter-cations within the lead halide networks has led to constructive energy funneling and morphological improvements, luminescence properties of these materials were found to be greatly enhanced. As a result, device luminance and external quantum efficiencies of such perovskite light-emitting diodes have accelerated expeditiously. In this study, various organic counter-cations in the form of aromatic amino compounds were used as ligand additives for the inorganic CsPbBr3 perovskite. These compounds were added in different mole percentage and various properties of the final deposited films were probed. The size and structure of these molecules play an important role in the formation of the final perovskite phase, thus exerting a strong influence on the photoluminescence and electrical properties. The device performance based on each molecular additive is finally compared and correlated to their film properties, thereby evaluating their effectiveness to function as ligands in the multidimensional perovskite framework.

Authors : Heesoo Park1, Fahhad H Alharbi1,2, Stefano Sanvito3, Nouar Tabet1,2 and Fedwa El-Mellouhi1
Affiliations : 1 QEERI, HBKU, Doha, PO Box 34110, Qatar. 2 College of Science and Engineering, HBKU PO Box 34110, Doha, Qatar. 3 School of Physics, AMBER and CRANN Institute, Trinity College, Dublin 2, Ireland.

Resume : Perovskite oxides are generally insulators due to the localization of valence electrons and the relatively low energy level in an O atom. This large bandgap is an obstacle to applications of optoelectronic devices. And, in a perovskite structure, the radius of O anion leads to accommodate an alkali metal whose cation radius is smaller than in perovskite halides. Thus, it may require a proper atomic arrangement of the constituent elements when a compound poses a relatively large cation such as Cs , CH3NH3 . In an effort of searching for new photoactive compounds among I-V-VI3 group perovskites and the derivatives, we performed density functional theory (DFT) calculations comparing the thermodynamics stabilities and bandgaps. In this work, we quantified the thermodynamics stabilities of perovskites while oxides are substituted with chalcogenide (S2-, Se2-, Te2-). Comparing the perovskite with the corresponding stable compounds, we find the total energy between them can be reduced. However, the perovskite structures are unstable despite the increase of radii of anions. Interestingly, this work led us to discover new stable compounds by estimating the convex hull energy using the formation energy in open databases. The calculated band gaps and absorption coefficients describe that these compounds are photoactive in the visible light spectrum. We will discuss the stabilities and physical properties regarding the structural feature of octahedra and the constituent elements. Acknowledgments: This work is sponsored by the Qatar Environment and Energy Research Institute (FE, FHA and NT). Computational resources have been provided by the research computing team at Texas A&M University at Qatar. This work is supported by the Qatar National Research Fund (QNRF) through the National Priorities Research Program (NPRP8-090-2-047)

12:30 Lunch Break    
Engineering of Perovskite Solar Cells II : Michael Saliba
Authors : Ross A. Kerner, Tracy Schloemer, and Barry P. Rand
Affiliations : Ross A. Kerner: Princeton University, Tracy Schloemer: Colorado School of Mines, Barry P. Rand: Princeton University,

Resume : We demonstrate that PbI2 reacts with aliphatic amines to produce Pb-amide species and ammonium molecules. This chemistry occurs in solution, at gas/solid interfaces, and in all solid-state systems suggesting that Pb-amide incorporation into state-of-the-art perovskite films is highly plausible. The amide species acts as a pseudohalide meaning the amine/amide reaction is capable of simultaneously passivating A-site and X-site vacancies. Furthermore, we comment on the effects of sub-stoichiometric (PbI2 rich) precursor formulations as well as the stability of strained Pb-amide bonds. Finally, the reactions are shown to occur due to ?self-exposure? of ammonium halide perovskite as amines are released during degradation and degradation catalyzed by interfaces with noble metals. These results reveal that the chemistry of halide perovskites is significantly more complex than is commonly assumed. This work identifies detailed reaction mechanisms influencing the passivation, stability, and interpretation of common characterization techniques. The insight it provides is useful to facilitate targeted improvements to perovskite optoelectronic device performance and stability.

Authors : Efrain Ochoa-Martinez, Sandy Sanchez, Michael Saliba, Evgeniia Sheveleva, Fryderyk Lyzwa, Christian Bernhard
Affiliations : Adolphe Merkle Institute, University of Fribourg, Fribourg, 1700, Switzerland; Adolphe Merkle Institute, University of Fribourg, Fribourg, 1700, Switzerland; Adolphe Merkle Institute, University of Fribourg, Fribourg, 1700, Switzerland; Physics Department, University of Fribourg, Fribourg, 1700, Switzerland; Physics Department, University of Fribourg, Fribourg, 1700, Switzerland; Physics Department, University of Fribourg, Fribourg, 1700, Switzerland

Resume : The need to scale up the processes involved in the production of perovskite solar cells (PSC) has resulted in several potential candidates which can take PSCs from the current laboratory scale to large area modules. One of these techniques capable of producing devices with the throughput required in industry is the Flash Infrared Annealing (FIRA); this process is able to produce fully crystallized MAPbI3 perovskite films resulting in devices with power conversion efficiencies as high as 18.3%, within seconds and without the need for an antisolvent [1]. The crystal size domains of the films are larger than 50 μm. However, in spite of its simplicity and large grain size, FIRA devices still lack in efficiency when compared with highest performance PSCs. One possibility that could explain this difference is an increase of the indirect component in the bandgap of the FIRA cells. The existence of a direct-indirect bandgap nature on MAPbI3 perovskites has already been reported [2, 3]. In the present work this behaviour is analysed through spectroscopic ellipsometry at room temperature, the study is extended to other compositions of perovskites like MAPbBr3, and FAMAPbBrI which exhibit similar properties. References [1] S. Sanchez, X. Hua, N. Phung, et Al., Adv. Energy Mater. (2018), 1702915. [2] X. Ke, J. Yan, A. Zhang, et Al., Applied Physics Letters (2015), 107, 091904. [3] E. M. Hutter, M. C. Gélvez-Rueda, A. Osherov, et Al., Nature Materials (2017), 16, 115–120.

Authors : Marina.I.Ustinova[1], Filipp S. Talalaev [2], Sergey D. Babenko [3], Sergey Yu. Luchkin [1], Pavel A. Troshin [1,2]
Affiliations : 1)Skolkovo Institute of Science and Technology, Moscow, Russia 2)Institute for Problems of Chemical Physics of RAS, Chernogolovka, Russia 3)The Branch of Talrose Institute for Energy Problems of Chemical Physics of Russian Academy of Sciences, Semenov Prospect 1/10, Chernogolovka, Moscow region, 141432, Russia

Resume : Recently discovered lead halide based perovskites demonstrated outstanding electronic characteristics and showed high efficiencies of >22% in solar cells. Even though perovskite solar cells can potentially accomplish a revolution on the PV market due to high efficiency and low cost, their practical application is limited severely by low stability and high toxicity of complex lead halides. Therefore, many research groups worldwide explore new materials in order to find some environment-friendly alternatives to the conventional lead perovskites. Bounassisi et al. have reported recently theoretical and spectroscopic study pointing toward InI as a promising material for photovoltaics (Chem. Mater. 2017, 29, 4667-74). Here we present the first experimental study proving that InI indeed can be used as active layer material in photovoltaic cells delivering encouraging external quantum efficiency of 17% at short wavelengths.The overall power conversion efficiency (<1%) of the devices was limited mainly by low open circuit voltages and fill factors even after substantial optimization of interfacial layers, film thickness and morphology. Strong photoconductivity effect revealed for thin films of InI allowed us to apply this material for fabrication of efficient photodetectors with lateral and vertical geometries. Both types of devices showed excellent light sensitivity and short response times pointing towards high potential of further development of this research direction.

Authors : Muhammad Talha Masood [1], Syeda Qudsia [1], Simon Sandén [2], Oskar J. Sandberg [2], Mathias Nyman [2], Paola Vivo [3], Peter D. Lund [4], Ronald Österbacka [2], Jan-Henrik Smått [1]
Affiliations : [1] Laboratory of Physical Chemistry and Center of Excellence for Functional Materials, Åbo Akademi University, Porthansgatan 3-5, 20500 Turku, Finland, [2] Physics and Center of Excellence for Functional Materials, Åbo Akademi University, Porthansgatan 3-5, 20500 Turku, Finland, [3] Tampere University of Technology, P.O. Box 541, FI-33101 Tampere, Finland, [4] Aalto University and School of Science, P.O. Box 15100, FI-00076 Aalto, Finland.

Resume : Perovskite solar cells (PSCs) have proven to be a promising new photovoltaic technology, which potentially could outshine the conventional silicon-based solar cell technology, as their record efficiencies to date are close to 23%. However, before the PSC technology can break into the photovoltaics market, issues related to the poor reproducibility of the currently used processing methods have to be solved. Our approach is to utilize the dip coating method [1] to improve the quality and to better understand the functions of the compact and mesoporous TiO2 layers in PSCs. These layers are important for the selective charge extraction and for controlling the crystallization of the perovskite layer, respectively. By tuning the sol composition and the dip coating parameters, uniform TiO2 thin films can be prepared, [1] while further addition of block copolymers produces well-ordered porous structures. These accurate processing tools have allowed us to study the influence of the compact TiO2 layer in detail [1] as well as investigating the charge selectivity of similar layers in organic solar cells [2]. We are also currently working on replacing the conventional particle-based nanostructured TiO2 layer with an ordered porous layer, which will allow for a better control and easier study of the perovskite crystallization process. [1] M.T. Masood, et al., ACS Appl. Mater. Interfaces, 9, 17906 (2017). [2] O.J. Sandberg, et al., Phys. Rev. Lett., 118, 076601 (2017).

15:15 Closing Remarks    

Symposium organizers
Chittaranjan DASTechnical University Darmstadt

Otto-Berndt-Str. 3, 64287 Darmstadt, Germany
Derya BARAN BRYANTKing Abdullah University of Science and Technology (KAUST)

KAUST Solar Center 23955, Thuwal, Saudi Arabia
MAIN ORGANIZER: Malgorzata KOT (SOWINSKA)BTU Cottbus-Senftenberg

Konrad-Wachsmann-Allee 17, 03046 Cottbus, Germany

+49 (0) 355 69 2972
Michael SALIBAUniversity of Fribourg

Adolphe Merkle Institute, Chemin des Verdiers 4, CH-1700 Fribourg