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Energy materials


Doping and charge transport processes in organic and hybrid materials for energy applications

Doping and charge transport are key processes to enhance electrical, thermal and optical functions in organic and hybrid materials. They underpin emerging energy saving and bioelectronic devices. The symposium will bring together key investigators to discuss challenges and perspectives of widespread applications of organic and hybrid electronics.


Scope of the symposium is to bring together the experimental and theoretical communities to discuss new challenges and perspectives in the areas of doping and charge transport processes in organic and hybrid functional materials. Such themes have been the subject of in-depth investigations in the past, however new findings are challenging the traditional structure-property paradigms, which have been driving the materials design and modeling up to now. The doping mechanisms and the role of dopants in governing the structural and functional properties of either high-charge carrier mobility polymers or perovskites is not well understood yet. New molecular-design methods, dopants and doping techniques are continuously enhancing the values of parameters such as the electrical conductivity, Seebeck coefficient and redox activities, paving the way for organic and hybrid materials to emerging applications such as thermoelectric, supercapacitors and bioelectronic devices.

Great challenges still have to be faced, mainly regarding:

Materials Synthesis

  1. Design and synthesis of new organic semiconductors including both small molecule and polymeric conjugated materials
  2. Design and synthesis of new dopant systems
  3. Design and synthesis of new hybrid materials

Materials and Device Characterization

  1. Fundamental understanding of the various doping mechanisms
  2. Overcome limited processability and control over the microstructure of doped films
  3. Fundamental understanding of the intrinsic chemical instability of n-doped films

Materials Modeling

  1. Modeling morphology and structural properties of doped organic and hybrid materials.
  2. Modeling the spectroscopic properties of doped organic and hybrid materials.
  3. Understanding charge and thermal transfer dynamics in functional materials via multi-scale first principles simulations.

Hot topics to be covered by the symposium:

  • Fundamental mechanisms of bulk and interface doping.
  • Structural, optical, electronic, and thermoelectric properties of doped organic and hybrid materials.
  • Charge transport in intrinsic and doped systems.
  • First-principles methods for charge and thermal transport properties in doped organic and hybrid materials.
  • Steady-state and time-dependent vibrational and electronic spectroscopies in doped materials.

List of invited speakers (confirmed):

  • Thomas Anthopoulos (KAUST) – OFET and materials
  • Michael Chabinyc (UCSB) – organic thermoelectric
  • Adam Moulé (UC Davis) – doping in organic materials
  • Christian Mueller (Chalmers University) – materials chemistry and doping
  • Martijn Kemerink (Linköping University) – doping and device physics
  • Alberto Salleo (Stanford University) – structure-property relationships, doping
  • Antonio Facchetti (Northwestern University) – materials chemistry, OFET, PV
  • Mariano Campoy-Quiles (ICMAB-CSIC) – polymer, perovskite solar cells
  • Mario Caironi, (IIT) – device phyiscs, organic thermoelectric
  • Jana Zaumseil (Heidelberg University) – nanotubes, OECT
  • John Grey, (Uni. New Mexico) - spectroscopy of organic semiconductors
  • Koen Vandewal (Hasselt Uni.) – charge recombination in organic solar cells
  • Natalie Banerji (Uni. Bern) - molecular spectroscopy of organic semiconductors
  • Fabrizia Negri (Uni. Bologna, Italy) – charge transport modeling, organic
  • Veaceslav Coropceanu (Georgia Tech, US) – electron-phonon couplings
  • Jenny Nelson (Imperial College London, UK) – modeling device physics
  • Xavier Blase (CNRS, France) – modeling doping in organic materials
  • Klaus Meerholz (Uni. Cologne) - OLED, device physics


Selected papers will be published in the journals Advanced Materials Technologies and Advanced Electronic Materials (Wiley-VCH).

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Openings / Doping : Daniele Fazzi
Authors : Karl Leo
Affiliations : IAPP, TU Dresden, Germany

Resume : Organic semiconductors with conjugated electron systems are currently intensively investigated for many novel electronic and optoelectronic applications. We have introduced controlled electrical doping /1/ as a key technology for efficient OLEDs, which is broadly commercially used, despite the fact that the microscopic mechanisms have been controversially discussed. In this talk, I will summarize research findings on controlled molecular doping: we have recently clarified the basic mechanisms of doping in organics /2/. Activation energies as low or even lower as those observed in doped inorganic semiconductors like silicon are possible. For many applications, however, the key parameter is not the charge carrier generation efficiency, but the conductivity achieved by doping and in particular the activation energy of the conductivity, which should be as low as possible. In a recent study /3/, we have comprehensively studied these parameters and related them to the molecular structures. /1/ K. Walzer et al., Chem. Rev. 107, 1233 (2007) /2/ M. Tietze et al., Nature Comm. 9, 1182 (2018) /3/ M. Schwarze et al., Nature Materials 18, 242 (2019)

Authors : Ian E. Jacobs,1 Gabriele D?Avino,2 Yue Lin,1 Vincent Lemaur,3 Yuxuan Huang,1 Xinglong Ren,1 Dimitrios Simatos,1,4 William Wood,1 Chen Chen,1 Thomas Harrelson,5 Tarig Mustafa,1,4 Christopher A. O?Keefe,4 Leszek Spalek,1 Dion Tjhe,1 Martin Statz,1 Lianglun Lai,1 Peter A. Finn,6 William G. Neal,6 Joseph Strzalka,7 Christian B. Nielsen,6 Jin-Kyun Lee,8 Stephen Barlow,9 Seth R. Marder,9 Iain McCulloch,10,11 Simone Fratini,2 David Beljonne,3 Henning Sirringhaus1
Affiliations : 1. Optoelectronics Group, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK 2. Grenoble Alpes University, CNRS, Grenoble INP, Institut Neel, 25 rue des Martyrs, 38042 Grenoble, France 3. Laboratory for Chemistry of Novel Materials, University of Mons, Mons, B-7000 Belgium 4. Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK 5. Molecular Foundry, Lawrence Berkeley National Laboratory, One Cyclotron Road Building 67, Berkeley, CA 94720, USA 6. School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, E1 4NS, UK 7. X-Ray Science Division, Argonne National Laboratory, Lemont, IL, 60439 USA 8. Department of Polymer Science & Engineering, Inha University, Incheon, 402-751 South Korea 9. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States 10. KAUST Solar Center, Physical Sciences and Engineering Division (PSE), Materials Science and Engineering Program (MSE), King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia 11. Department of Chemistry, University of Oxford, Oxford, UK

Resume : The last decade has seen renewed interest in the fundamentals of doping processes in semiconducting polymers.[1] Molecular doping has been the most studied approach, in large part because films are easy to fabricate and show high conductivities. However, molecular doping is subject to several limitations: 1. disorder due morphological disruption from dopant ions; 2. limited charge densities due to insufficiently strong dopants; 3. reduced doping efficiency from charge transfer complexation; and 4. poor stability resulting from the inherent reversibility of charge transfer. These difficulties largely stem from the dual role molecular dopants must play. The neutral dopant first acts as a redox agent, while the product of this redox reaction?the ionized dopant?then acts as a compensating ion. A recently proposed method[2] based on ion exchange allows for replacement of the dopant counter-ion with arbitrary ion from an electrolyte solution. This separates the redox and charge compensation steps, and enables the fabrication of doped films with a range of different counterions. The improved microstructural control this process allows enables us for the first time to systematically address a longstanding but still poorly understood question: what limits the electrical conductivity at the high doping levels relevant to organic thermoelectrics? Is it the formation of charge carrier traps in the Coulomb potentials of the counterions, or is it the structural disorder in the polymer lattice? Here[3] we present a simple framework for understanding ion exchange doping and evaluate a wide range of charge transfer dopants and electrolytes. From this systematic study, we identify a set of experimental conditions which allows for extremely high doping levels of approaching 1 charge per monomer and nearly 100% ion exchange efficiency in several different polymer classes. In each of these degenerately doped polymer systems, we achieve record or near-record conductivities: >1200 S/cm for PBTTT, 220 S/cm for P3HT, 80 S/cm for DPP-BTz, and 15 S/cm for IDTBT. Most critically, we show that in this regime conductivity is poorly correlated with ionic size, but strongly correlated with paracrystalline disorder. This observation, backed by a detailed electronic structure model that incorporates ion-hole and hole-hole interactions and a carefully parameterized model of disorder, indicates that trapping by dopant ions is negligible, and hence that the doping efficiency in these systems is near 100%. Our results imply that in this high carrier density regime, relevant to thermoelectric devices, maximizing crystalline orderis the most critical factor in improving conductivity. This realization, along with the greatly improved control enabled by ion exchange, provides a clear path forward for the design of polymer thermoelectrics. 1. Jacobs, I. E., Moulé, A. J., Adv. Mater. 2017, 29, 1703063 2. Yamashita, Y. et al. Nature 2019, 572, 634?638 3. Jacobs, I. E., et al. arXiv:2101.01714

Authors : S. Demchyshyn, M. Verdi, L. Basiricò, A. Ciavatti, B.Teklemariam, M. Kaltenbrunner, B. Fraboni
Affiliations : JKU Linz; University of Bologna; University of Bologna; University of Bologna; JKU; JKU; University of Bologna

Resume : The demand for large area, low cost and flexible high-energy radiation detection systems for security and medical imaging, has pushed the research to develop novel detectors combining high sensitivity and low-cost fabrication. Recently, lead-halide perovskites emerged as another very promising novel materials family for X- and gamma-ray detection. Their success can be attributed to perovskites strong absorption of ionizing radiation, due to the presence of heavy atoms as Pb, I, Br, together with high charge carrier mobilities, long exciton diffusion and long charge carrier lifetime. However, thin film detectors are characterized by a limited absorption of radiation, thus crucial roles in the detection performance are played by material stabilization, dark current reduction and efficient charge collection. In photodiode architecture, these issues can be overcome through interface engineering [9]. In this work, we used devices with a p-i-n photodiode architecture with hole and electron transport layers (HTL, ETL) directly interfaced with a 500 nm thick perovskite film (Cs0.05(FA0.83MA0.17)0.95PbI3-xBrx), deposited from solution and acting as high-energy photons absorber. Several devices that differ for buffer layers, ETL and HTL layers have been fabricated to optimize the photodiode characteristics through interface engineering, i.e. dark current reduction, low hysteresis, and efficient charge transport and collection. The interface materials studied are PEDOT:PSS and nickel oxide (NiOx) as hole transporting layers; N,N?-dimethyl-3,4,9,10-perylentetracarboxylic diimide (PTCDI), phenyl-C61-butyric acid methyl ester (PCBM) as electron transport layer. Bathocuproine (BCP), titanium oxide (TiOx) and chromium oxide (Cr2O3) were employed as buffer layer between the ETL and the top metal contact. The different interfaces were characterized with electrical measurement in dark conditions and under 40kV X-ray beam to investigate their contribution on principal detector performance parameters like sensitivity, dark current, and limit of detection (LoD).

11:00 DISCUSSION    
Materials : Simone Fabiano
Authors : Antonio Facchetti
Affiliations : Northwestern U. and Flexterra Corp.

Resume : In this presentation we report the correlation between polymer structure and charge transport in solution-processed indium oxide (In2O3):polymer blend films by using several polymers having different amine nitrogen atom atomic content (N%). These amine containing polymers control the electron mobilities of the semiconducting oxide films by tuning the carrier/trap concentrations via a combination of electron transfer/doping and charge trap/scattering center formation, effects which depend on the polymer species and loading contents in the metal oxide matrix. All polymer addition enables the formation of more ductile semiconductor metal oxide films, as measured in a flexible thin-film transistor architecture. However, while PVP addition reduces the field-effect mobility vs. the pristine (no polymer added) In2O3 matrix, for all other N-containing polymers there is always a certain polymer weight addition to the In2O3 precursor formulation which increases the mobility of the In2O3 matrix. Equally interesting, increasing N% in the polymer from 0% in polyvinyl phenol (PVP) to 34% in polyethyleneimine (PEI), the electron doping capacity gradually increases, enabling to increase the polymer content in the formulation at which the mobility is maximized from 0 wt.% to 1.0 wt.%, thus further enhancing blend ductability. Note, the positive effect of the N-containing polymer remains effective even with a polymer (PVP-NH2) having a N% as low as 3.9%, Finally, we discovered correlations between the electron donating capacity of the polymer, charge transport, polymer chemical structure and thermal stability, as well as elemental composition in the final In2O3-polymer blend film.

Authors : Peter A. Finn [1], Ian E. Jacobs [2], William Neal [1], Huiyan Zeng [3], John Armitage [2], Viktoriia Untilova [3], Ruiheng Wu [4], Bryan D. Paulsen [5], Mark Freeley [1], Matteo Palma [1], Jonathan Rivnay [5,6], Henning Sirringhaus [2], Martin Brinkmann [3], Christian B. Nielsen [1]
Affiliations : [1] School of Biological and Chemical Sciences and Materials Research Institute, Queen Mary University of London, London, England; [2] Optoelectronics Group, University of Cambridge, Cavendish Laboratory, Cambridge, England; [3] Institute Charles Sadron, Université de Strasbourg, Strasbourg, France; [4] Department of Chemistry, Northwestern University, Evanston, IL, 60208, USA; [5] Department of Biomedical Engineering, Northwestern University, Evanston, IL, 60208-3109, USA; [6] Simpson Querrey Institute, Northwestern University, Chicago, IL, 60611, USA

Resume : Organic semiconducting materials for thermoelectrics is a rapidly expanding area of energy harvesting and promising applications in low level self-powered devices and renewable energy. The efficiency of thermoelectric materials is increased via high power factor and electrical conductivity against a low thermal conductivity. Organic materials have inherently low thermal conductivity making them a viable alternative to inorganic based materials however there is much work to be done on increasing electrical conductivity. Electrical conductivity, governed by charge carrier mobility and concentration, for organic semiconductors can be increased by doping. Addition of a chemical species that can oxidise (reduce) organic semiconducting polymers create additional electron holes (electrons) and therefore increase electrical conductivity, yet it is still important to understand the polymer:dopant interactions to enable the rational design of materials that exhibit better doping efficiency and charge carrier mobility. Herein, we have synthesised a series of random co-polymers using different thiophene-based monomers and a range of different monomer ratios. We have explored in detail how structural changes of the co-polymers are linked to energetics, charge carrier mobility and doping efficiencies. We will discuss how these findings can be used to alter electric and thermoelectric properties.

Authors : Raphael Pfattner, Victor Lebedev, Elena Laukhina, Marta Mas-Torrent, Vladimir Laukhin, Concepció Rovira and Jaume Veciana
Affiliations : Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC) Campus UAB, 08193 Bellaterra (Spain) and Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN) ICMAB-CSIC, 08193 Bellaterra (Spain)

Resume : The first [BEDT-TTF = bis(ethylenedithio)- tetrathiafulvalene based quasi-twodimensional organic superconductor ?-(BEDT-TTF)2I3 was first reported back in 1984.[1] Soon it became clear that ion radical salts (IRSs) derived from BEDT-TTF exhibit tuneable electronic band structures; therefore, such molecules are excellent building blocks for engineering a rich and diverse family of organic crystalline metals and semiconductors. Electronic band structures of BEDT-TTF-based molecular conductors originate from ordered arrangements, such as stacks and layers, leading to metallic charge-transfer salts with partially filled bands.[2] One interesting characteristic of BEDT-TTF-based crystalline conductors is the very deformable molecular and crystal structure with strong electron?electron and electron?phonon couplings. Thanks to this, their anisotropic electronic structures exhibit many fascinating electronic and structural phase transitions caused by lattice deformations, which can be controlled by external stimuli such as light, temperature, strain, pressure, and humidity, among others. Nevertheless, it is necessary to engineer these crystals into a proper material for sensing applications. This is done by forming polycrystalline layers of IRSs, derived from BEDTTTF-based conductors, in nanocomposite bilayer (BL) films. Developing smart materials that can respond to an external stimulus is of major interest in artificial sensing devices able to read information about the physical, chemical and/or biological changes produced in our environment. Additionally, if these materials can be deposited or integrated on flexible, transparent substrates, their appeal is greatly increased. Such properties can be further tuned by choosing the nature of the IRSs enabling high sensitivity towards strain, pressure, temperature or even contactless radiation sensing i.e. bolometers.[3,4] In another very recent example, bilayer films, composed of conducting polycrystalline layers of two dimensional BEDT-TTF-IRSs, hydroresistive sub-micron sized crystals on top of a polymeric host matrix permit to electrically monitor relative humidity in a stable and fully reversible fashion.[5] Mechanisms of responses are discussed and correlated with fundamental properties of charge transport in these systems. This sensor platform enables combining high electrical performance of single crystals with processing properties of polymers towards a simple, low-cost and highly sensitive platform for applications in robotics, biomedicine and human health care. [1] E. B. Yagubskii, I. F. Shchegolev, V. N. Laukhin, P. A. Kononovich, M. V. Kartsovnik, A. V. Zvarykina, L. I. Buravov, JETP Lett. 1984, 39, 12. [2] J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H. H. Wang, A. M. Kini, M.-H. Whangbo, Organic Superconductors (Including Fullerenes): Synthesis, Structure, Properties and Theory; Prentice Hall: Englewood Cliffs, NJ, 1992. [3] E. Laukhina, R. Pfattner, L. R. Ferreras, S. Galli, M. Mas?Torrent, N. Masciocchi, V. Laukhin, C. Rovira, J. Veciana. Advanced Materials, 2009, 21, 1-5. [4] R. Pfattner, V. Lebedev, E. Laukhina, S. Chaitanya Kumar, A. Esteban?Martin, V. Ramaiah?Badarla, M. Ebrahim?Zadeh, F. Pelayo García de Arquer, G. Konstantatos, V. Laukhin, C. Rovira, J. Veciana. Advanced Electronic Materials, 2015, 1, 1500090. [5] R. Pfattner, E. Laukhina, L. Ferlauto, F. Liscio, S. Milita, A. Crespi, V. Lebedev, M. Mas-Torrent, V. Laukhin, C. Rovira, J. Veciana, ACS Appl. Electron. Mater. 2019, 1, 1781.

12:15 DISCUSSION    
Authors : Christian Müller
Affiliations : Chalmers University of Technology, Göteborg, Sweden

Resume : Molecular doping is an essential tool for all facets of organic electronics, from thin-film transistors and solar cells to bulk materials for e-textiles and thermoelectrics. While the fundamentals of doping are increasingly well understood, several challenges remain. Typically, an excessive amount of dopant is needed to reach a high number of charge carriers, which can disturb both the electrical and mechanical performance. Moreover, dopant molecules diffuse, which complicates doping of millimeter-thick bulk materials, and limits the stability of the doped state. In my talk, I will discuss our recent work on conducting bulk materials, from foams to fibers, and explore the interplay of electrical and mechanical properties. Further, I will cover doping of more polar conjugated polymers that carry oligoethylene glycol side chains. Improved compatibility of polar polymers with dopant molecules eases processing, leads to a higher electrical conductivity, and improves the thermal stability. Finally, I will introduce the concept of double doping. Polymers with a sufficiently low ionisation energy are able to transfer two electrons to each dopant molecule, which allows to halve the amount of required dopant.

Authors : Martin Brinkmann (1), Yuhan Zhong (1) , Vishnu Vijayakumar (1), Mounib Bahri (2), Laure Biniek (1), Viktoriia Untilova (1), Laurent Herrmann (1), Nicolas Leclerc (3)
Affiliations : (1) Université de Strasbourg, CNRS, Institut Charles Sadron, UPR 22, F-67000 Strasbourg, France (2) Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR7504 CNRS, Université de Strasbourg, 23 rue du loess, 67037 Strasbourg, Cedex 03, France (3) Université de Strasbourg, CNRS, ICPEES UMR 7515, F-67087 Strasbourg, France

Resume : This study presents an effective design strategy of polymer thermoelectric materials based on structural control in doped polymer semiconductors. The strategy is illustrated for two archetypical polythiophenes e.g. poly(2,5-bis(3-dodecyl-2-thienyl)thieno[3,2-b]thiophene) (PBTTT) and regioregular poly(3-hexylthiophene) (P3HT). FeCl3 doping of aligned films results in charge conductivities up to 10^5 S/cm and metallic-like thermopowers similar to iodine-doped polyacetylene. The films are almost optically transparent and show strongly polarized polaronic bands (dichroic ratio > 10). The comparative study of structure-property correlations identifies three conditions to obtain such record conductivities: i) achieve high in-plane orientation of conjugated polymers with high persistence length, ii) ensure uniform chain oxidation of the polymer backbones by regular intercalation of dopant molecules in the polymer structure without disrupting alignment of pi-stacked layers and iii) maintain a percolating nano-morphology along the chain direction. The anisotropic conducting polymer films are ideal model systems to investigate the correlations between thermopower S and charge conductivity sigma. Different S versus sigma correlations are observed along and perpendicular to the chain direction. The simultaneous increase of charge conductivity and thermopower along the chain direction results in a substantial improvement of thermoelectric power factors up to 2 mW.m-1.K-2.

Authors : Mihaela Girtan-1, Romain Mallet-2, Marcela Socol-3, Anca Stanculescu-3
Affiliations : 1- Photonics Laboratory, (LPhiA) E.A. 4464, SFR Matrix, Université d?Angers, Faculté des Sciences, 2 Bd Lavoisier, 49045 Angers, France, 2- SCIAM, SFR ICAT, Université d?Angers, 4 Rue Larrey, 49033 Angers, Cedex 09, France, 3- National Institute of Material Physics, 405A Atomistilor Street, 077125 Bucharest-Magurele, Romania,

Resume : PEDOT:PSS is one of few organic transparent conducting semiconductors which can be used as electrode for OLED, organic or perovskite solar cells. In this paper a complete characterization from optical, morphological, electrical, photo-electrical and thermo-electrical point of view was done for PEDOT:PSS thin films and DMSO and EG sensitized PEDOT:PSS films. The studies on the electrical conductivity and electrical photoconductivity allowed the calculation of different relaxation times. The relaxation time of the electrical conductivity is or order of femtosecond and is multiply by a factor 10 when PEDOT:PSS thin films were deposited on surfaces sensitized with DMSO and EG. Besides, the photoconduction excitation and relaxation times are of order of seconds. An increase of the relaxation photoconduction time by 2 was observed for films deposited on surfaces sensitized with DMSO and by 1.2 for films deposited on surfaces sensitized with EG. The time response of electrical conductivity after exposure to light add supplementary knowledge for the understanding of the inertial processes, or hysteresis behavior of organic or perovskite solar cells involving PEDOT:PSS films. The electrical conductivity increase with the temperature and the use of DMSO and EG as surfactants lead to higher values of electrical conductivity and Seebeck coefficient. A better stability of the electrical conductivity with the temperature increase, was remarked for films deposited on surfaces sensitized with DMSO.

15:00 DISCUSSION    
Authors : Michael L. Chabinyc
Affiliations : University of California Santa Barbara

Resume : The effects of electrical doping of semiconducting polymers are complex due to the interplay between transport properties and microstructure. We will discuss our recent work in understanding the mechanisms of electrical doping of semiconducting polymers. In-situ X-ray scattering was used to follow the changes in microstructure of poly(3-hexylthiophene) during doping using an electrochemical transistor. A sharp change in the structure of crystalline domains of P3HT occurs at high carrier concentration suggesting a change in the location of the counter ions in the bulk. By measuring the thermopower in electrochemical transistors, changes in the electronic density of states (DOS) with carrier concentration can be determined. The broadening of the DOS helps to explain recent models connecting the electrical conductivity and thermopower. A power law form for the DOS of doped semiconducting polymers near the Fermi level provides a reasonable fit to the dependence of transport and thermopower on carrier concentration. The implications of this behavior for improvement of the thermoelectric properties of polymers will be discussed.

Authors : Weidong Tang (1,2), Tianjun Liu (1,2), Xiaoming Zhao (2) Jianwei Li (3) Zilu Liu (3), Fabiola Liscio (4), Silvia Milita (4), Bob C Schroeder (3) and Oliver Fenwick.(1,2)*
Affiliations : 1 School of Engineering and Material Sciences, Queen Mary University of London, Mile End Road, E1 4NS, United Kingdom. 2 The Organic Thermoelectrics Laboratory, Materials Research Institute, Queen Mary University of London, Mile End Road, London, E1 4NS, United Kingdom. 3 Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, United Kingdom. 4 Istituto per la Microelettronica e Microsistemi (IMM)-Consiglio Nazionale delle Ricerche (CNR), Via Gobetti 101, 40129 Bologna, Italy.

Resume : Halide perovskites have emerged as promising candidates for photovoltaics and light-emitting diodes. Recently, promising thermoelectric performance has been reported for single nanocrystals of a halide perovskite and thin films, but there is limited understanding of how thermoelectric performance can be optimised, especially in thin films where a diverse range of structures and morphologies are accessible. This work will report the thermoelectric figure of merit (ZT) for a lead-free halide perovskite. This result is in part due to the ultralow thermal conductivity of our films (0.38 W/mK at room temperature), as well as high electrical conductivity enabled by self-doping of the films through controlled Sn oxidation. The oxidation process can be modulated by incorporation of a mixed halide surface layer, which acts as an additional optimisation parameter for ZT whilst also making the material more stable. We quantify both the Lorenz number and the thermal boundary resistance in these materials and show how modified deposition processes can significantly enhance stability.

Authors : Ye Liu, Diego Rosas Villalva, Anirudh Sharma, Md Azimul Haque, Derya Baran
Affiliations : Ye Liu; Diego Rosas Villalva; Anirudh Sharma; Md Azimul Haque; Derya Baran ? Physical Science and Engineering Division, KAUST Solar Center (KSC), King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia;

Resume : Molecular doping is a powerful tool to tune the thermoelectric (TE) properties of solution-processed semiconductors. In this work, we prepared a binary composite and doped both of its constituents, that is, naphthalene diimide?bithiophene copolymers (PNDI2ODT2) and single-walled carbon nanotubes (SWCNTs), by a 1H-benzimidazole derivative (N-DMBI). The doped composites show an n-type character and an in-plane TE figure of merit (ZT), exceeding the values obtained with the doped polymers. UPS and UV?vis?NIR absorption spectra confirm that n-type doping of both the copolymer and the SWCNTs was achieved by the same doping process. The use of SWCNTs consistently results in a higher ?. Furthermore, an SWCNT content up to 9 wt % does not compromise the low thermal conductivity of the polymer matrices, leading to a ZT value of 0.0045. The n-type composites show good solution processability and relatively stable Seebeck coefficients upon air exposure for 8 months. Doping of copolymer/SWCNT composites offers more solutions for easy-processable and n-type materials.

16:15 DISCUSSION    
Authors : Thomas D. Anthopoulos
Affiliations : King Abdullah University of Science and Technology (KAUST), KAUST Solar Centre, Thuwal 23955-6900 (Saudi Arabia)

Resume : Molecular doping is frequently used in organic semiconductor-based devices to tune their operating characteristics. Despite the offered versatility, however, the use of doping in best-in-class devices, such as high mobility organic thin-film transistors (OTFTs) and efficient organic photovoltaics (OPVs), remains limited. In this presentation I will present various examples of organic (opto)electronic devices where the incorporation of molecular dopants not only allows for the tuning of their operating characteristics but also enables record performance to be achieved. Particular emphasis will be placed on the multifunctional role of several known as well as new dopant molecules, the synergistic effects of which can lead to remarkable device characteristics.

Authors : Mariano Campoy Quiles
Affiliations : Institute of Materials Science of Barcelona, ICMAB-CSIC, Campus UAB, Bellaterra, 08193, Spain

Resume : Electrical doping is attracting strong interest as a tool to improve different types of organic based devices, such as transistors (OFETs) and thermoelectric generators (OTEGs). In this contribution, I will introduce two novel methodologies that allow to spatially pattern doping in conjugated polymers. First, we fabricated polymer samples with a controlled lateral gradient of molecular doping [DOI: 10.1021/acs.macromol.9b02263]. Combining this type of samples with local probes, we obtain large datasets removing errors associated to sample-to-sample variations. We use these samples as a high-throughput methodology to find optimum doping level for thermoelectric materials. Moreover, we employ samples with gradients to investigate the thermal conductivity of doped polymer films. Interestingly, doping reduces thermal conductivity with respect to undoped films, which strongly suggests a new phonon scattering mechanism upon molecular doping [DOI: 10.1021/acsenergylett.0c01410]. Finally, we present a fast method to pattern composition with diffraction limited resolution, which allows to produce patterns of electrical conductivity. This method is based on the laser induced diffusion of dopants through a semipermeable membrane [DOI: 10.1038/s41467-020-17361-8].

17:45 DISCUSSION    
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Charge transport, structure-function I : Sophia Hayes
Authors : Nicolas F. Zorn, Merve Balc? Leinen, Felix J. Berger, Daniel Heimfarth, Francesca Scuratti, Andrea Perinot, Mario Caironi, and Jana Zaumseil
Affiliations : Institute for Physical Chemistry & Centre for Advanced Materials, Universität Heidelberg, D-69120 Heidelberg, Germany; Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, 20133 Milano, Italy

Resume : Solution-processed networks of semiconducting, single-walled carbon nanotubes (SWCNTs) have attracted considerable attention as materials for next-generation (opto-)electronic devices including thermoelectrics. For all those applications understanding and quantifying mobile charge carriers that can be created by chemical, electrochemical or electrostatic doping is required. SWCNT networks exhibit excellent ambipolar carrier mobilities and have strong optical signatures that are associated with charges (e.g., trion absorption and emission). Here we present examples of monochiral (6,5) SWCNT networks that were of chemically, electrochemically or photo-doped to modulate their conductance and to correlate it with their optical signatures such as photoluminescence, absorption and Raman spectra (ACS Appl. Mater. Interfaces 2018, 10, 11135, J. Phys. Chem. C 2019, 123, 22680, Adv. Electron. Mater. 2020, 6, 2000717). Furthermore, we apply charge modulation absorption (CMS) and photoluminescence spectroscopy (CMPL) to probe and characterize the mobile charge carriers (holes and electrons) in monochiral (6,5) and mixed SWCNT network field-effect transistors (ACS Nano 2020, 14, 2412). Ground-state bleaching and charge-induced trion absorption features, as well as exciton quenching and their dependence on network composition, applied voltage and modulation frequency are discussed.

Authors : Jenny Nelson, Xingyuan Shi, Anders S Gertsen, Jack Coker, Martin P. van der Schelling, Roderick C. I. Mackenzie and Jarvist Moore Frost
Affiliations : Jenny Nelson, Xingyuan Shi, Jack Coker, Martin P. van der Schelling and Jarvist Moore Frost: Department of Physics, Imperial College London, London SW7 2AZ, UK. Anders S Gertsen: DTU Energy, Danish Technical University, Denmark. Roderick C. I. Mackenzie: Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK.

Resume : Charge transport in organic semiconductors such as conjugated polymers proceeds through a combination of intrachain and interchain charge transfer events. The large conformational phase space of conjugated polymers leads to disorder in the energies of charge sites and results in dispersive and temperature-dependent charge carrier dynamics. The distribution of site energies and resulting charge transport characteristics could, in principle, be inferred from the chemical structure of the material, although this is seldom straightforward. In the limit of very stiff polymers with low conformational freedom, transport will become limited by the nature of the interchain contact points. In this work we focus on two conjugated polymers featuring different degrees of conformational freedom. In the case of poly(9,9-dioctyl fluorene) (PFO) we show that hole transport can be limited by formation of a specific conformational defect, the beta-phase conformer, and that the impact of the defect on the density of states, hole transport dynamics and temperature dependent transport can be explained quantitatively in terms of the impact of the defect on the polymer?s electronic structure [1]. To explore the case of intra-chain transfer-limited hole transport we study the stiff indacenodithiophene-co-benzothiadiazole polymer (C16-IDTBT). We observe a weak degree of charge trapping, consistent with the stiff conformation indicated by persistence length measurements and molecular dynamics (MD) simulations and the corresponding electronic structure. In films of this polymer, hole mobility is limited relative to transport in isolated polymer, showing that interchain charge transfer in films is the rate limiting step. This is confirmed by kinetic Monte Carlo modelling of hole transport within chain assemblies modelled using MD simulations. We conclude by reviewing the factors that will ultimately limit charge transport in conjugated polymers. [1] X. Shi et al., Physical Review X (2019) DOI: 10.1103/PhysRevX.9.021038

11:00 DISCUSSION    
Perovskite : Simone Fabiano
Authors : Klaus Meerholz
Affiliations : University of Cologne, Germany

Resume : Charge transport in semiconductors is a crucial process that defines efficiency for optoelectronic devices such as solar cells and light‐emitting diodes. Semiconducting organic–inorganic metal halide perovskites (PVSK) have recently been the focus of intense research, motivated largely by the rapid rise in efficiency of next‐generation solar cells based on these materials. However, understanding the physical processes which govern charge transport within PVSK materials and ultimately the device performance is still on a relatively early stage of development. One problem, many groups are facing is the rather poor reproducibility of cell fabrication. To get deeper insight, we introduce a novel experimental technique derived from photo‐EMF induced by running grating (RG) technique to study the photophysical properties of PVSK materials. This initial experimental investigation of RG photo‐EMF was performed in at 633 nm wavelength. We confirm that MAPbI3 can be described as bipolar photoconductor with extremely short dielectric relaxation times flowed by slow processes in photoconductivity relaxation for both types of carriers. The RG Technique allows to determine a number of crucial material parameters such as the electron and hole photoconductivity relaxation time, the ambipolar diffusion length, and the minority carriers drift mobility. We have determined these parameters for a series of samples with different processing conditions – allowing us to draw crucial structure‐property relations. Thus, the general features of the photoconductivity mechanism in PVSK semiconductors will be discussed.

Authors : Teresa Gatti
Affiliations : Center for Materials Research, Justus Liebig University Giessen

Resume : The development of novel hole transporting materials (HTMs) which can improve the stability of lead-halide perovskite solar cells (PSCs) operating in ambient conditions is a valuable strategy to address the future commercialization of this ultra-cheap photovoltaic technology. Among other HTMs, we have identified poly(3-hexylthiophene) (P3HT), a highly soluble and easy-to-process from solution semiconducting polymer, to be a good compromise for ensuring decent efficiencies to PSCs at relatively low-costs in comparison with the benchmark HTM based on the Spiro-OMeTAD small molecule. Spiro-OMeTAD indeed requires doping with LiTFSI and tert-butyl pyridine additives to be sufficiently active for hole transport and, in this regard, we have recently demonstrated an up-to-now unknown mechanism of de-doping induced by the latter additive, that we will discuss in this contribution.[1] To boost the charge extraction/transport properties of P3HT-based HTMs, we previously employed a composite strategy, adding to the P3HT phase small amounts of nanocarbon fillers.[2,3] This type of composite HTMs is also beneficial for device stability, in that it increases the hydrophobicity of the layer, thus retarding the deleterious action of water molecules on the photoactive perovskite layer. Following this direction of investigation, we looked for other possible nanomaterials to couple with P3HT for the development of even more efficient HTMs and stable PSCs. We will thus discuss here the outcomes of our most recent contribution, [4] in which we suggest that a CuSCN nanoplateletes/P3HT composite, combining hole extraction and transport properties with water oxidation activity, transforms incoming water molecules and triggers the in situ p-doping of the conjugated polymer, improving transport of photocharges. Insertion of the nanocomposite into a lead perovskite solar cell with a direct photovoltaic architecture causes stable device performance for 28 days in high-moisture conditions. Our findings demonstrate that the engineering of a hole extraction layer with water-splitting additives could be a viable strategy to reduce the impact of moisture in perovskite devices. References [1] F. Lamberti, T. Gatti, et al. Chem 2019, 5, 1806-1817 [2] T. Gatti et al. Adv. Funct. Mater. 2016, 26, 7443-753 [3] T. Gatti et al. Solar RRL, 2018, 2, 1800013 [4] M. Kim et al., T. Gatti, F. Lamberti Commun. Mater. 2021, 2, 6

Authors : Jarla Thiesbrummel, Vincent M. Le Corre, Francisco Peña-Camargo, Fengjiu Yang, Steve Albrecht, Dieter Neher, Henry J. Snaith, and Martin Stolterfoht
Affiliations : Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, UK; Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam-Golm, Germany; Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam-Golm, Germany; Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin, Kekule? Straße 5, D-12489 Berlin, Germany; Young Investigator Group Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin, Kekule? Straße 5, D-12489 Berlin, Germany; Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam-Golm, Germany; Clarendon Laboratory, Department of Physics, University of Oxford, Oxford OX1 3PU, UK; Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476 Potsdam-Golm, Germany

Resume : The power conversion efficiency of mixed metal lead-tin perovskite solar cells still lags behind those of their full-lead equivalents. One reason for this is that Sn2 is easily oxidised to Sn4 , which leads to the formation of charge carrier trap states and to p-doping. Though several strategies have been developed to prevent or limit this oxidation, the degradation of the perovskite layers upon exposure to oxygen remains problematic. Moreover, the exact influence of self-doping on the performance of lead-tin perovskites is poorly understood. On top of that, other factors that could strongly affect device performance, such as the influence of mobile ions, have barely been explored for this system. Here, we take a closer look at the origin of current losses in lead-tin perovskite solar cells and find that, beside optical losses, the cells also suffer from significant charge collection losses. Voltage dependent photoluminescence (PL) measurements at open-circuit (VOC) demonstrate a signigificant reduction in PL upon a switch from open- to short-circuit, indicative of efficient charge extraction. However, then the PL rises again over the course of several seconds, before stabilising at about 6% of the PL value obtained at VOC. The current decays on the same timescales as the extraction becomes less efficient due to band flattening, amounting to a loss of 1.4 mA cm-2 under 1 sun illumination. In the following, we show that the reduction in the charge extraction efficiency and band flattening is linked to the movement of mobile ions in the perovskite rather than electronic charge (doping) and we show that this effect is well reproduced by numerical simulations. Importantly, as far as we could assess in this research, doping in mixed lead-tin perovskites is not directly causing current losses as the doping density is insufficient to screen the built-in field. Finally, we generalise our findings to lead-based perovskites, where we also find that the timescales of the band flattening and current loss correspond to the timescales of mobiles ions. Hence, the mechanisms appear to be generic for Pb and Pb/Sn based perovskites, which paves the way towards understanding a key loss mechanism in perovskite cells.

12:15 DISCUSSION    
Charge transport, structure-function II : Christian NIELSEN
Authors : Koen Vandewal
Affiliations : IMO-IMOMEC, Hasselt University, Wetenschapspark 1, 3590 Diepenbeek, Belgium

Resume : Many organic electronic devices contain interfaces between electron donating (D) and electron accepting (A) materials. The new, intermolecular electronic states in which an electron is transferred from D to A, are termed charge-transfer (CT) states. Ground-state CT in host-dopant systems results in an increase in conductivity,[2] while D-A blends where the CT state is an excited state are used in organic solar cells, photodetectors and so-called ?exciplex? OLEDs.[2] In this talk, I will discuss the fundamental processes of CT state recombination and dissociation and its impact on device performance. Furthermore, some new applications of CT complexes, including organic near-infrared detectors with peak detection wavelengths up to 1700 nm, will be discussed.[3-5] [1] Nature Communications 9, 1182 (2018) [2] Nature Materials 18, 459 (2019) [3] Nature Communications 8, 15421 (2017) [4] Advanced Materials 29, 1702184 (2017) [5] Chemistry of Materials 31, 9325.(2019)

Authors : Olivier Bardagot1, Sanne Govaerts2, Gonzague Rebetez1, Priscila Cavassin1, Frederic Schneider1, Julien Réhault1, Wouter Maes2, Natalie Banerji1
Affiliations : 1 Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern; 2 UHasselt ? Hasselt University, Institute for Materials Research (IMO), Design & Synthesis of Organic Semiconductors (DSOS), Agoralaan, 3590 Diepenbeek, Belgium

Resume : From energy storage to healthcare, organic mixed ionic-electronic conductors (OMIECs) are the cornerstones of a wide range of applications.[1,2] With the aim of promoting rational molecular engineering, increasing attention is being paid to understanding the fundamental processes governing their electrochemical doping.[3] In this work, we elucidated the doping mechanisms of a series of polythiophene (co)polymers with various types of side chains using an innovative characterization method. In recent years, side chain engineering has proven to be effective to increase both the doping extent and the ion/charge transport properties of a given polymer backbone. Two strategies prevail: 1) the use of polar side chains to facilitate ion penetration,[4] and 2) copolymerising units with apolar/ionic side chains to optimise device performances.[5] Yet, the combination of these two strategies, i.e. mixing polar/ionic side chains, remains unexplored. Therefore, we designed a 50/50% copolymer to evaluate the synergic effect offered by mixing polar/ionic side chains. The electrochemical doping mechanisms governing this innovative copolymer was compared with those of reference polymers composed of 100% apolar (P3HT), 100% polar (P3MEEET) and 100% ionic (bis(tri-fluoromethane)sulfonimide = TFSI)[6] side chains. Our characterization method combines a home-built spectroelectrochemistry setup with organic electrochemical transistor geometry in order to correlate the doping extent with the ion/charge transport. We elucidated (i) the relationship between channel conductivity and the neutral, polaron and bipolaron populations using multivariate curve resolution (MCR) analysis, and (ii) the doping kinetics driving the performance of these (co)polymers based on coupled spectral/electrical in operando time resolved measurements, with a time-resolution of few milliseconds. Our results indicate that combining the two dominant strategies is beneficial to reach faster doping, thereby encouraging the use of mixed polar/ionic side chains in the design of the next generation of OMIECs for electrochemical devices. [1] D. Moia, A. Giovannitti, A. A. Szumska, I. P. Maria, E. Rezasoltani, M. Sachs, M. Schnurr, P. R. F. Barnes, I. McCulloch, J. Nelson, Energy & Environmental Science 2019, 12, 1349?1357. [2] B. D. Paulsen, K. Tybrandt, E. Stavrinidou, J. Rivnay, Nature Materials 2020, 19, 13?26. [3] B. D. Paulsen, R. Wu, C. J. Takacs, H.-G. Steinrück, J. Strzalka, Q. Zhang, M. F. Toney, J. Rivnay, Advanced Materials 2020, 32, 2003404. [4] L. Q. Flagg, C. G. Bischak, J. W. Onorato, R. B. Rashid, C. K. Luscombe, D. S. Ginger, J. Am. Chem. Soc. 2019, 141, 4345?4354. [5] P. Schmode, D. Ohayon, P. M. Reichstein, A. Savva, S. Inal, M. Thelakkat, Chem. Mater. 2019, 31, 5286?5295. [6] S. Govaerts, J. Kesters, M. Defour, B. Van Mele, H. Penxten, S. Neupane, F. U. Renner, L. Lutsen, D. Vanderzande, W. Maes, European Polymer Journal 2017, 97, 49?56.

Authors : Marija Knezevic (1), Marie Erard (1), David Berardan (2), Isabelle Lampre (1), Christophe Colbeau-Justin (1), Mohamed Nawfal Ghazzal (1)
Affiliations : 1. Institut de chimie physique, UMR 800 CNRS, Université Paris Saclay, Orsay; 2. ICMMO, UMR 8182 CNRS, Université Paris Saclay, F-91405, Orsay

Resume : Over the past decade, metal halide perovskites (MHP, CsPbX3: X = Cl, Br, I) have been widely investigated as promising materials for optoelectronics, achieving a record-breaking efficiency in solar cells.[1] From a fundamental point of view, MHP could be excellent candidates for photocatalysis due to their high photogenerated charge-carrier production and mobility as well as their narrow and tunable bandgap energy.[2] MHP with tuneable bang-gap energy could be obtained through fast substitution of bromide by iodine or chloride (CsPbBr3-yXy : X = Cl, Br, I).[3] In this presentation, we investigated charge-carrier lifetime and dynamics in CsPbBr3-yXy along with interfacial electron transfer from CsPbBr3-yXy to TiO2 by means of time resolved photoluminescence (TRPL) and transient absorption spectroscopy (TAS). The results show that the bandgap engineering and the position of the conduction band and valence band level in both materials are detrimental for optimal interfacial charge transfer. We will present the optimal bandgap configuration for the most efficient charge injection in correlation with the anionic ratio substitution. Charge-carrier injection from one material to another resulted in increased charge-carrier lifetime, which could positively affect the photocatalytic activity. [1] P. V. Kamat, ACS Energy Lett. 2019, 4, 1055?1056. [2] R. A. Scheidt, E. Kerns, P. V. Kamat, J. Phys. Chem. Lett. 2018, 9, 5962?5969. [3] G. Nedelcu, L. Protesescu, S. Yakunin, M. I. Bodnarchuk, M. J. Grotevent, M. V. Kovalenko, Nano Lett. 2015, 15, 5635?5640.

15:00 DISCUSSION    
Modelling charge transport : Daniele Fazzi
Authors : Fabrizia Negri
Affiliations : Università di Bologna, Dipartimento di Chimica "Giacomo Ciamician" and INSTM, UdR Bologna

Resume : Understanding relationships between structure and opto-electronic properties is an important goal for the materials science of organic semiconductors, motivated by the desire to improve material performance. In this perspective, one major objective is to achieve a deep understanding of the interplay between intramolecular properties and intermolecular interactions governing, among others, charge conduction mechanisms, energy transfer, optical properties of molecules and aggregates.[1] Organic semiconductors with extended-core ? systems may display, in some cases, di-radical / multi-radical character. Organic molecules with unpaired electrons are intriguing for advanced applications in molecular electronics, spintronics and organic batteries, as well as other possible applications. [2] A distinctive character of conjugated diradicals is the location of the double-exciton state, a low lying excited state dominated by the doubly excited HOMO,HOMO->LUMO,LUMO configuration.[3] In this contribution I will summarize some results of recent computational investigations in my group, encompassing the study of charge transport parameters in cycloparaphenylene (CPP) carbon based nanohoops[4], the characterization of organic semiconductors featuring di-radical character with particular focus on the identification of the double-exciton state[5-7], the hole/electron delocalization in mixed valence systems [8], the low lying electronic excited states of molecular aggregates[9]. [1] C. Wang, H. Dong, L. Jiang, W. Hu., Chem. Soc. Rev., 2018, 47, 422. [2] Hu, X.; Wang, W.; Wang, D.; Zheng, Y. J. Mater. Chem. C 2018, 6, 11232. [3] Di Motta S., Negri F., Fazzi D., Castiglioni C., Canesi E. V. J. Phys. Chem. Lett., 2010, 1, 3334. [4] S. Canola, C. Graham, A. J. Pérez-Jiménez, J.C. Sancho-García, F. Negri, Phys. Chem. Chem. Phys. 2019, 21, 2057. [5] S. Canola, J. Casado, F. Negri, Phys. Chem. Chem. Phys., 2018, 20, 24227. [6] S. Canola, Y. Dai, F. Negri, Computation, 7, (2019), 68 [7] G. Salvitti, F. Negri, Á. J. Pérez-Jiménez, E. San-Fabián, D. Casanova, J. C. Sancho-García, J. Phys. Chem. A. 124 (2020), 3590. [8] P. Mayorga Burrezo, W. Zeng, M. Moos, M. Holzapfel, S. Canola, F. Negri, C. Rovira, J. Veciana, H. Phan, J. Wu, C. Lambert, J. Casado, Angew. Chem. Int. Ed., 2019, 58, 14467. [9] W. Liu, S. Canola, A. Köhn, B. Engels, F. Negri, R. F. Fink, J. Comp. Chem., 2018, 39, 1979.

Authors : Tahereh Nematiaram and Alessandro Troisi
Affiliations : Dept. of Chemistry and Materials Innovation Factory, University of Liverpool, Liverpool L69 7ZD, U.K.

Resume : We answer one of the most challenging questions in the field of organic electronics: ??How to reduce the dynamic disorder??? Answering this question has been difficult as the available theoretical methods/experimental techniques could not evaluate this property for more than a handful (~15) of materials. Since the dynamic disorder is one of the main factors limiting the charge mobility, not having any design principle to limit it means that trial and error methods remain the main approach to improve mobility. We utilize the largest existing database of computed dynamic disorders (developed in our group - composed of ~5000 entries) to devise practical design principles to reduce the dynamic disorder. We find that the strength of dynamic disorder is highly correlated with the gradient of transfer integral, a property easily computable for any molecular orientation. We also show that orientations of molecular pairs with just few atoms in contact are more likely to yield low dynamic disorder. This observation is highly counterintuitive as for years the focus has been to maximize the number of pi-stacked atoms and now this result is showing the other optima. Other properties with meaningful influence on the dynamic disorder include the presence of alkyl chains, the strength of transfer integral and the presence of heavy atoms. The findings of this work provide important design principles for low-disorder high-mobility molecular semiconductors.

Authors : Thomas F. Harrelson (a) , Varuni Dantanarayana (b), Makena Dettmann (c), Daniel Vong (c), Tahereh Nematiaram (d), Luke L. Daemen (e) , John E. Anthony (f), Barry P. Rand (g), Alessandro Troisi (d), Nir Goldman (h), Roland Faller (a), Adam J. Moule (a)
Affiliations : (a) University of California, Davis - Department of Chemical Engineering (b) University of California, Davis - Department of Chemistry (c) University of California, Davis - Department of Materials Science (d) Liverpool University - Department of Chemistry (e) Oak Ridge National Lab - Spallation Neutron Scource (f) University of Kentucky - Department of Chemistry (g) Princeton University - Department of Physics (h) Lawrence Livermore National Lab

Resume : Recent theories suggest that low frequency dynamic intra- and intermolecular motions are critical to determining localization of the charge carrier, and thus, control the hole mobility. We used inelastic neutron scattering (INS) to probe thermal disorder directly by measuring the high resolution phonon spectrum in multiple small molecule OSCs. We achieved near perfect agreement between the INS spectra of OSC crystals and first principle electronic simulations. This simulation is used to generate a set of electron-phonon coupling parameters, which are used to compute hole mobility using transient localization theory. The charge mobility, calculated from first principles, is in excellent quantitative agreement with macroscopic measurements. We note however, that most OSCs are not extended crystals. Instead most OSCs are a mixture of multi-crystalline and amorphous domains. The electronic simulation method used in our first study (plane-wave DFT) is much too computationally expensive to include chemical, structural, or even orientational disorder. So even though it is possible to measure a low energy phonon spectrum using INS in a polymeric or multi-crystalline sample, it was until now not possible to model the spectrum. We developed two multi-scale modeling techniques to model phonons in disordered samples and allow us to quantitatively validate the models using INS spectra. For this presentation, amorphous ruberene will be used to demonstrate how amorphous samples can be modeled using molecular dynamics and benzo-di-thiophene trimers will be used to explore the role of dihedral bonds.

16:15 DISCUSSION    
POSTER : Daniele Fazzi
Authors : Po-Chih Chen, Sheng-Hsiung Yang*
Affiliations : Institute of Lighting and Energy Photonics, College of Photonics, National Chiao Tung University

Resume : Organic/inorganic hybrid perovskites have received a great deal of attention in solar energy harvest due to their high absorbance in the visible range, long carrier diffusion length, high conversion efficiency and solution processibility for large area production. It is extremely important to develop high-quality hole transport layer (HTL) to replace PEDOT:PSS for fabricating efficient and stable perovskite solar cells (PSCs) for long-term durability. Upon this consideration, potassium-doped nickel oxide (K:NiOx) layer via the sol-gel process was proposed to improve the conductivity and to modify its work function. To reach charge balance in our devices, a quaternary ammonium salt tetrabutylammonium tetrafluoroborate (TBABF4) was added into PCBM as the electron transport layer. Inverted PSCs with the configuration of FTO/K:NiOx/CsFAMAPb(BrI)3/PCBM TBABF4/TIPD/Ag were fabricated and evaluated. The results revealed that the photovoltaic device based on 3 wt% K-doped NiOx showed the best performance with an optimized PCE of 17.05% and a high fill factor of 74%, and it retained about 80% initial PCE value after 35 days storage. This research provides a simple and effective approach to fabricate PSCs with high efficiency and long-term stability for future production.

Authors : R. Avetisov*, I. Taydakov**, A. Zakharova*, K. Barkanova*, R. Sayfutyarov*, A. Barkanov*, I. Avetissov*
Affiliations : *D. Mendeleev University of Chemical Technology of Russia **P. N. Lebedev Physical Institute of RAS

Resume : Synthesis and purification (up to 99.995 wt%) of asymmetric complex of tris(4,4,4-trifluoro-1-(4-biphenyl)butane-1,3-dionato) (1,10- phenanthroline) europium(III) Eu(BFTA)3(Phen) has been carried out. The annealing of the crystalline preparations under controlled temperature (190-230 C) and partial pressures of ligands (BFTA, Phen) let's plotted the p(BFTA)-p(Phen)-T diagram of different Eu(BFTA)3(Phen) polymorphs. We succeeded to control the luminescent and transport properties of crystalline preparations. Besides the chemical activity estimated as a dissolving rate in CHCl3 was varied in orders of magnitude. TEM analysis showed that according to the annealing condition we observed atomic defects in the form of Eu-vacancies in the crystalline structures. Multilayer OLED structures prepared by thermal vacuum sputtering in which the Eu-FFT was used as an emitting agent demonstrated different electroluminescent properties depending on Eu-vacancies concentrations in the initial preparations. The research was supported by Russian Science Foundation by the grant 19-79-10003.

Authors : Irinela Chilibon
Affiliations : National Institute of Research and Development for Optoelectronics, INOE-2000 Optospintronics 409 Atomistilor Str., P.O. Box MG-5 077125, Bucharest-Magurele, Romania 4021.457.45.22

Resume : The most common sources of energy available in the environment, frequently used for the extraction of electricity are: wind, solar energy, temperature and stress or pressure. Piezoelectric generators are appropriate to convert the smallest mechanical deformations directly into electrical energy. Piezoelectric materials have the capability to generate a small amount of current, when they are subjected to mechanical pressure, such as pushing, bending, twisting, and turning. A vibrating piezoelectric device differs from a typical electrical power source in that it has capacitive rather than inductive source impedance, and may be driven by mechanical vibrations of varying amplitude. Some structures can be tuned to have two natural frequencies relatively close to each other, resulting in the possibility of a broader band energy harvesting system. The energy produced by piezoelectric materials is in many cases far too small to directly power an electrical device. The progress in the device innovation happens where Microelectromechanical Systems (MEMS) technologies overlap with smart technologies. For intelligent sensor systems this means a trend from miniaturized sensor to the smart and miniaturized sensor systems, which can integrate processing functions in a minimal space. Acknowledgements: The author is grateful for the financial support of Ministry of Research and Innovation (MCI), 2021 Core Program, and Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFISCDI).

Authors : Devanshi Bhardwaj, A. M. Umarji
Affiliations : Materials Research Centre, Indian Institute of Science, Bengaluru, India - 560012

Resume : Vanadium dioxide (VO2) has been extensively studied for various applications due to a reversible first order phase transition (TSMT = 68 oC). Though, its use is restricted due to its high transition temperature and low visible transmission. Theoretically, Scandium is proposed as the potential dopant to influence the semiconductor to metal transition and optical spectrum by increasing the visible transmittance (inducing a blue shift in the spectrum). Herein, we try to validate these theoretical results experimentally. Nano-crystalline powders and thin films of Scandium-doped VO2 (ScxV1-xO2) were synthesised using a novel, rapid non-equilibrium Solution Combustion Route and Ultrasonic Nebulised Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) respectively followed by a reduction, in two steps. Influence of Scandium doping on increasing the band gap (blue shift) is sought to be achieved (change in band gap from ~1.7 eV for undoped to ~2.02 eV for x=0.02). Phase transition was studied by DSC on bulk and by I-V measurements on thin films where no change in the transition temperature was observed. The optical results were in good agreement with that obtained theoretically. Thus, the present work validates the theoretical prediction that Sc can induce blue shift in the VO2 system thereby, making it a potential dopant for modulating the optical spectrum for smart window applications.

Authors : Stefania Porcu(a), Micaela Castellino(b), Ignazio Roppolo(b), Carlo Maria Carbonaro(a), Simonetta Palmas(c) Laura Mais(c), Maria Francesca Casula(c), Svetlana Neretina(d), Robert A. Hughes(d), Francesco Secci(e), Pier Carlo Ricci(a)
Affiliations : a) Department. of Physics, University of Cagliari, S.p. no. 8 Km 0,700, 09042 Monserrato (Ca), Italy b) Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino, 10129, Italy c) Department of Mechanical, Chemical, and Materials Engineering INSTM and University of Cagliari, Via Marengo, 3 ? 09123 Cagliari, Italy d) Department of Aerospace and Mechanical Engineering, University of Notre Dame, 370 Fitzpatrick Hall, Notre Dame, IN 46556 e) Department of Chemical and Geological Science, University of Cagliari, S.p. no. 8 Km0700, 09042 Monserrato (Ca), Italy

Resume : Eco-sustainable solutions for the neutralization of air and water pollutants have increasingly gravitated toward the use of heterogeneous photocatalysts. This approach, which transforms pollutants into harmless substances through a light-driven chemical reaction on a catalytic surface, must comply with eco-sustainability requirements and be easily applicable. Semiconductor-based photocatalysis is a promising pathway for the degradation of environmental pollutants and, among all the various semiconductors used, titanium dioxide has proved itself to be the foremost material for environmental remediation due to its highly desirable photocatalytic properties. Titanium dioxide, however, poorly exploits the visible part of the electromagnetic spectrum due to the relatively large band-gap of its anatase phase, and as such, the UV portion of the solar spectrum is largely responsible for its photocatalytic activity. Herein, we demonstrate a highly efficient visible light hybrid catalyst based on titanium dioxide and phenyl carbon nitride (PhCN). With the organic component providing a broad absorption up to 600 nm and fast charge exchange to the conduction band of TiO2, the combination allows for the highly efficient photocatalytic degradation of Rhodamine B under visible excitation.

Authors : T. Degousée (1), V. Untilova (2), V. Vijayakumar (2), X. Xu (3), M. Palma (3), F. Liscio (4), S. Milita (4), M. Brinkmann (2), L. Biniek (2), O. Fenwick (1).
Affiliations : [1] School of Engineering and Materials Science, Queen Mary University of London, London E1 4NS, UK. [2] Institut Charles Sadron, Université de Strasbourg ? CNRS, Strasbourg, France. [3] School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK. [4] Istituto per la Microelettronica e Microsistemi (IMM)-Consiglio Nazionale delle Ricerche (CNR), Via Gobetti 101, 40129 Bologna, Italy.

Resume : Charge transport in conjugated polymer films is well-known to be dependent on the nanoscale film morphology. The same is true for thermal transport. The process of doping, which is key for polymer thermoelectric applications, may alter that morphology in subtle but important ways. This work will show that doping not only modulates charge carrier concentration and electrical conductivity, but can also have a significant effect on thermal conductivity with implications for ZT. In this work we will present different starting morphologies using drop cast films and also highly aligned polymer films formed by high-temperature rubbing. The latter technique produces near 100% alignment of the polymer chains along the rubbing direction. The structural and thermoelectric properties of these films are monitored as a function of doping. We will show that alignment of the polymer chains strongly enhances the thermal conductivity and also observe an electronic contribution to the thermal transport upon doping. However, doping of isotropic films caused an unexpectedly high thermal conductivity (>1 W/mK), far beyond the electronic contribution predicted by the Wiedemann-Franz law. The modified morphology adopted by the polymer after doping appears as the key parameter in the improved thermal transport. Despite the high thermal conductivity phases adopted by the polymer, we show that chain alignment can improve the figure of merit, ZT, in a polymer by a factor of 25, demonstrating the importance of morphological control in developing polymer thermoelectric materials.

Authors : K.I.Runina*, P.V.Strekalov*, M.N.Mayakova**, A.V.Khomyakov*, I.V.Taydakov***, R.I.Avetisov*, O.B.Petrova*, I.Ch.Avetissov*
Affiliations : * D. Mendeleev University of Chemical Technology of Russia ** A.M.Prokhorov General Physics Institute RAS *** P.N.Lebedev Physical Institute of the RAS

Resume : Organic-inorganic luminescent hybrid materials (HM) based on inorganic matrices are promising for OLED application, in new devices of passive, active and integrated optics and photonics. New HM?s were synthesized by high temperature methods: 1) glass-melt technique with low-melting glass matrices in PbF2-B2O3 and PbF2-B2O3-SiO2-ZnO systems; 2) by solid-phase synthesis with PbF2, CaF2, BaF2 and ZnO; 3) by low temperature methods: co-precipitation with PbF2, CaF2, BaF2 from aqueous solutions by hydrofluoric acid and ammonium fluoride. As organic constituents we used highly efficient phosphors of ?-diketone complex of Eu or Nd and 8-hydroxyquinoline complexes of Li, Zn, Al. The photoluminescence spectra showed that the same emitting centers were formed at high-temperature and at low-temperature syntheses. The formation of centers resulted from an exchange reaction leading to the creation of new complexes. At solid phase synthesis the exchange reaction started from 100 C and completed at 300 C. The research was financially supported by Russian Science Foundation by the grant No 19-79-10003

Authors : Anu Babusenan, B. Pandey, S. C. Roy, Jayeeta Bhattacharyya
Affiliations : Department of Physics, IIT Madras

Resume : Recently, carbon quantum dots (CQDs) have found a lot of applications for biomedical imaging, sensors and optoelectronic devices due to their tunable and intense emission properties in the visible range. They are biocompatible and can be synthesized easily and economically. The enhancement in photoluminescence (PL) efficiency is essential for a wide range of applications. High-resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM) were used to identify the morphology of the materials. We achieved an increase in the total photoluminescence emission of CQD films by using a TiO2 nanotube (TNT) substrates, instead of glass. CQDs have core emission and surface state emission, we observed a higher CQD core emission and the presence of a strong surface state emission in the CQD:TNT composite. We determined the band alignment of the composite, which favored the carrier transfer. High-resolution X-ray photoelectron spectroscopy (XPS) was employed to identify and analyze the composition of the CQD surfaces, which create the mid-band gap states. We confirmed a threefold increase in PL from CQD due to the charge transfer from TNT.

Authors : Sunil Kumar, François Balty, Naama Sliti, Ngoc Duy Nguyen
Affiliations : SPIN lab, Physics Department, University of Liege

Resume : With the ever-increasing popularity and the rapid advancements in the field of perovskite solar cells, there is nowadays a need for standardized testing and analytical methods dedicated to this new generation of devices. The complex nature of these hetero-structured cells, with several functional layers at the heart of interlinked charge transport mechanisms, is associated to recombination losses which can lead to detrimental effects on the cell performances. The accurate measurement of those effects and their precise physical interpretation are key to the understanding of the correlation between device efficiency and material composition and quality. Understanding charge transport in materials can be achieved through a dedicated characterization by frequency domain techniques, such as electrochemical impedance spectroscopy (EIS), that are useful tools to characterize processes occurring on different time scales in solar cells. In this work, we successfully use EIS to compare the blocking properties of a thin TiO2 layer coated by ultra-sonic spray pyrolysis under different ambient atmospheres (air, O2 and N2) along with a commercial TiO2 suspension cured under ultra-violet light. The detailed analysis of the impedance spectra by electrical simulations suggests that the lack of oxygen during the process under N2 atmosphere could be related to a change of TiO2 quality which is ultimately responsible for enhanced charge carrier recombination at the anode and loss in cell performance. The results of this study are extended by an in-depth analysis of charge transport using an approach based on a variant of photo current spectroscopy in which the modulation of light intensity allows to capture a cell response that provides complementary information about charge carrier lifetime and electron-hole recombination dynamics.

Authors : D. K. Gorai, T. K. Kundu
Affiliations : Indian Institute of Technology Kharagpur, Kharagpur, WB, India-721302

Resume : Graphitic carbon nitride (g-C3N4) shows excellent possibility to enhance its visible-light photocatalytic performance by tuning its electronic and optical properties as well as bandgap via Li and P codoping. The Li and P codoped g-C3N4 is synthesized by the polymerization of melamine, lithium carbonate, and ammonium phosphate at elevated temperature and characterized the obtained sample. After Li and P codoping, the photocatalytic performance of g-C3N4 for rhodamine B (RhB) and methyl blue (MB) degradation increases by increasing visible light absorption and decreasing the band gap compared to the pristine g-C3N4. Theoretical results show that after codoping with Li and P, there is more strong delocalized HOMO and LUMO state and the reactive sites, which facilitate the migration of photogenerated charge carriers and hence enhanced the photocatalytic performance compared to the pristine g-C3N4. keywords: Graphitic carbon nitride, codoping, Photocatalysis, rhodamine B, methyl blue, HOMO-LUMO

Authors : Alessandro Pira (1), Alberto Amatucci (1) Elisa Pinna (1) Annalisa Vacca (2), Claudio Melis (3), Guido Mula (1,*)
Affiliations : 1.PoroSiLab, Dipartimento di Fisica, Università degli Studi di Cagliari, Cagliari, Italy 2. Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, Università degli Studi di Cagliari, Cagliari, Italy 3. Dipartimento di Fisica, Università degli Studi di Cagliari, Cagliari, Italy *Corresponding author e-mail address:

Resume : To build efficient environmental-friendly materials for energy applications, improved strategies and detailed control of the fabrication processes are required. For porous materials, the pore size affects both the pore filling process and the filling materials properties, especially from the electrical conductivity point of view. Here we studied hybrid porous silicon (PSi) /eumelanin interfaces using both experimental and computational modelling approaches. We show the effect of the pore diameter on the water molecules diffusion within the polymer-filled pores and on the consequent photocurrent generation capability of the hybrid. In a recent work, we calculated that eumelanin density increases up to 5 nm away from the silicon interface [1] and evidenced how the density increase affects the hybrid interface stability. In this work, the PSi layers were prepared using the Electrochemical NanoLithography, a process developed in our laboratory to ensure well controlled pore size and size distribution [2]. We demonstrate that while eumelanin in thin pores shows poor dependence of its conductivity from the humidity degree, a significantly different behavior with respect to its bulk properties, these properties are restored with larger pores. In particular, we show that, in the case of eumelanin, the wettability improvement allowed by larger pores induces an increase in the electrical conductivity and a significant improvement of the photogeneration lifetime (from few days to several months). This demonstrates how, by controlling the diffusion of H2O2 and H2O within the polymer using the spatial confinement of the organic component it is possible to control the system conductivity properties. This kind of study also opens the way to the understanding of chemical species mobility in polymers inserted within nanoscale pores by using porous silicon as a sensor of the polymer properties. Work partially supported by Regione Autonoma della Sardegna project CRP78744 ?EnAPSi: Energy applications with porous silicon? 1. Antidormi, A. et al. J. Phys. Chem. C 2018, 122, 28405 2. Pinna, E. et al. Materials 2019, 12, 2891

Authors : Marina Bondarenko, Peter Silenko, Yury Solonin, Andrey Ragulya, Nadezhda Gubareni, Maxim Zahornyi, Oleg Khyzhun, Natalia Yarova
Affiliations : Frantsevich Institute for Problems of Materials Science of NASU, Krzhyzhanovsky St. 3, 03142 Kiev, Ukraine

Resume : The development of new photocatalytic systems such as a photocatalytic TiO2-based system associated with graphitic carbon nitride (g-C3N4) for effectively obtaining of hydrogen through photocatalytic water splitting is one of the most promising areas of renewable energy. For efficient light utilization, the fabrication of g-C3N4/TiO2 composite material has attracted much attention. However, both pristine g-C3N4 and g-C3N4/TiO2 composite exhibits photoactivity in blue region of visible spectrum only. It is found that the doping of carbon nitride by oxygen significantly improves its photocatalytic properties. Therefore, to improve the photocatalytic activity of semiconductor photocatalyst, the coupling O-doped g-C3N4 (O-g-C3N4) with anatase TiO2 is a good strategy. New composite material O-g-C3N4/TiO2 was synthesized by gas phase method under the special reactionary conditions of the pyrolysis of melamine. Deposition of O-g-C3N4 (~5% O) on the anatase nanopowder particles is confirmed by XRD, IR, XPS, SEM, EDX methods. It is found by UV-Vis-DRS method, that O-g-C3N4/TiO2 photosensitivity is observed in the significant part of the visible light region and the band gaps of product is determined to be less than 2.38 eV. Constructing heterojunction structures of TiO2 and O-g-C3N4 may be used as a cost-effective way to avoid the drawbacks of each component and realize a synergic effect for boosting the photocatalytic activity of material for energy applications.

Authors : Ruei-Hong Shen, Sheng-Hsiung Yang
Affiliations : Institute of Lighting and Energy Photonics, College of Photonics, National Chiao Tung University

Resume : In this study, the low temperature method was adopted for the synthesis all-inorganic cesium lead bromide CsPbBr3 nanocrystals (NCs). To further improve film-forming and optoelectronic properties of CsPbBr3 NCs, a surface ligand diphenylammonium bromide (DPABr) was added from 0 to 0.15 mole fraction in proportion to the amount of oleylamine. By introducing 0.1 mole fraction of DPABr, the SEM and AFM results revealed that smooth and pinhole-free films of CsPbBr3 NCs were formed with a low surface roughness of 4.6 nm. The introduced bromide ions can passivate the surface vacancies of CsPbBr3 NCs and improve photoluminescence quantum yield (PLQY) from 38% to 72% compared with the pristine CsPbBr3 NCs. Moreover, shorter and ? electron-rich phenyl groups help to increase carrier injection into nanocrystalline core, preventing carriers from being hindered by oleic acid and oleylamine with longer alkyl chains. Therefore, the conductivity of the resulting CsPbBr3 NCs was augmented. The maximum brightness and current efficiency of the optimized device based on CsPbBr3 NCs with 0.1 mole fraction of DPABr were enhanced 2.3- and 3.3-fold, respectively, relative to the pristine one.

Authors : Meena Ghosh, Dr. Sreekumar Kurungot
Affiliations : Physical & Materials Chemistry Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune- 411008, India.

Resume : Aqueous electrolyte based rechargeable batteries are emerging as safe and promising energy storage technologies for stationary and portable applications. In this context, zinc metal batteries (ZMBs) have received unprecedented interest due to the high volumetric capacity, water compatibility, and low reduction potential of zinc metal. However, the development of ZMB technology is constrained by the low life span of ZMB, which originates from the dendrite-like structural evolution on the metallic zinc anode during repeated cycling of the cell. In this work, we have introduced the Nafion ionomer membrane's competency as a separator in aqueous ZMBs. The Nafion ionomer possessing anionic sulfonate groups tethered with tetrafluoroethylene based fluoropolymer-copolymer maintains a uniform Zn-ion flux and prevents the ion concentration gradient near the Zn anode surface. These intriguing characteristics of Nafion ionomer result in the homogeneous nucleation of Zn deposits during the electrochemical cycling of ZMBs, leading to the dendrite-free Zn anode. As a result, the lab-level ZMB cells (Zn anode coupled with vanadium oxide and manganese oxide cathodes) utilizing Nafion ionomer separator outperform the charge storage capacity and cycling stability of similar ZMB cells comprising traditional porous neutral separators. Hence, this work reveals the influence of different separators on the electrochemical performance of ZMBs and demonstrates the advantages of the cation-selective ionomer separator as a practical approach for improving the life span of ZMBs.

Authors : John Marc C . Puguan, Pramod Rathod, and Hern Kim
Affiliations : Myongji University

Resume : A hybrid smart window exhibiting dual chromic response properties based on ionene/polymer material was successfully engineered. The thermochromic poly(N-isopropylacrylamide) was blended with a viologen-tethered poly(ionic liquid) having electrochromism to produce a smart window that can adaptively control light transmittance and solar energy in response to multiple stimuli. The device can control optical transmission and solar energy transmission simultaneously or independently. With the material?s excellent solubility and film forming ability, the smart device can be fabricated with much flexibility and ease. Lastly, this device has an all-in-one layer configuration which makes a more compact and simplified design. With further tuning, this new hybrid material can pave the way for the design of next generation multifunctional smart window devices which can efficiently control energy in buildings.

Authors : Michael John Craig, Max Garcia-Melchor
Affiliations : Trinity College Dublin

Resume : Energy storage and utilization have enabled human development across the globe. The predominant sources of this energy ? wood, coal, oil, and gas ? have attendant carbon emissions associated with their use. These carbon emissions pollute the atmosphere and increase the risks associated with climate change, making renewably-sourced, carbon-free energy storage solutions are especially attractive. A prominent approach is to use electricity to drive an electrochemical reaction with products that store energy. Examples include battery and hydrogen energy storage. Molecular hydrogen energy storage via renewably-driven electrolysis has advantages over battery energy storage such as higher energy density and more potential for long-term storage. However, hydrogen produced via electrochemical water splitting is currently prohibitively expensive. An important source of this high cost is the material catalyzing the anodic reaction in the electrolyzer. The oxygen evolution reaction (OER) occurs here, involving the breaking of four O?H bonds from two water molecules to produce oxygen. Protons formed from this reaction go on to combine forming hydrogen at the cathode. Catalysts for the OER are either too expensive or too inefficient, with current state-of-the art catalysts composed of the high-cost precious metal iridium. I will be presenting computational investigations of studied molecular catalysts for this reaction, which have received comparatively little attention despite their impressive reactivity. By studying simulation results and experimental activity across a wide range of catalysts, we developed a new method of cataloging materials for this reaction.[1] This has impelled a study of 100s of hypothetical catalysts to enable the prediction of new catalysts, shown in Figure 2, where we categorize catalysts on the basis of their overpotential, which denotes the extra voltage we have to expend in the process of splitting water with a given catalyst. This analysis is the first large-scale analysis of molecular OER catalysts that compares the known activity of experimental catalysts to computational results across a wide array of complexes. We study the charge transport in these complexes and ultimately their application in hybrid catalytic systems. Typically, analyses of this size are done for heterogeneous catalysts, but the results garnered from this approach also help to explain results in heterogeneous catalysts. For example, we offer a theory-based explanation for the experimentally-observed OER enhancement in the presence of a magnet.[2] [1] Craig, M. J. et al. Nat. Commun. 10, 4993 (2019). [2] Garcés-Pineda, F. A., Blasco-Ahicart, M., Nieto-Castro, D., López, N. & Galán-Mascarós, J. R.. Nat. Energy 4, 519?525 (2019).

Authors : Guido Fratesi(1), Simona Achilli(1), Aldo Ugolotti(2), Alessandro Lodesani(3), Andrea Picone(3), Alberto Brambilla(3), Luca Floreano(4), Alberto Calloni(3), Gianlorenzo Bussetti(3)
Affiliations : (1) Dipartimento di Fisica "Aldo Pontremoli", Università degli Studi di Milano, I-20133 Milano, Italy; (2) Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, I-20125 Milano, Italy; (3) Dipartimento di Fisica, Politecnico di Milano, Leonardo da Vinci 32, I-20133 Milano, Italy; (4) Istituto Officina dei Materiali - CNR-IOM, Laboratorio TASC s.s. 14 km 163.5, 34149 Trieste, Italy;

Resume : Thin and ultra-thin films composed by organic molecules are key steps for the development of new generation devices in modern technology. Among the different organic compounds, so-called metal tetra-phenyl porphyrins (M-TPP) have shown special properties that make this class of organic molecules almost unique and exploitable for applications. Since different transition metal ions can be placed inside the porphyrin inner cavity, the charge state and other chemical, electronic and transport properties of the molecule can be tuned without changing the molecular skeleton. M-TPPs usually lie flat and show a square-lattice superstructure, as dictated by their shape, when they self-assemble onto several low-interacting substrates with different surface crystal orientations. This suggests to consider M-TPPs as a prototype system where the different regions of the molecule (inner cavity and border skeleton/phenyl groups, respectively) exhibit different chemical and physical properties. Such an assumption may guide experiments towards the growth of specific organic/inorganic interfaces, but requires specific studies in order to assess its validity and limits. In this work we systematically study the dependence of the adsorption properties on the central atom for Co-, Ni-, and Zn-TPP adsorbed on oxygen passivated Fe(001) [1], namely the Fe(001)-p(1x1)O surface, which is able to retain both the compositional and coordination integrity of molecules. It is found by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) that despite the weak molecule?substrate interaction, preserving many features of quasi-free molecules, the self-assembled structure switches from the (5x5)R37° superlattice of Co-TPP and Ni-TPP to the plain (5x5) of Zn-TPP. Ab initio calculations based on density functional theory (DFT) are used to investigate the adsorption properties of the different molecules and the possible overlayers formed. Adsorption energies, structures, and electronic properties allows us to discuss the bonding mechanisms and the magnetic character. Although differing substantially as for the LEED and STM experimental results, M-TPPs show only moderate energy differences are found, suggesting that, in the next future, theoretical analysis is call to a new challenge in view of elucidating the subtle effects that may steer the selection of the structure among overlayers with similar properties. [1] G. Fratesi, S. Achilli, A. Ugolotti, A. Lodesani, A. Picone, A. Brambilla, L. Floreano, A. Calloni, and G. Bussetti, Appl. Surf. Sci. 530, 147085 (2020)

Authors : Felix Utama Kosasih, Francesco Di Giacomo, Jordi Ferrer Orri, Elizabeth M. Tennyson, Weiwei Li, Narges Yaghoobi Nia, Mojtaba Abdi-Jalebi, Fabio Matteocci, Judith L. Driscoll, Samuel D. Stranks, Aldo Di Carlo, Giorgio Divitini, Caterina Ducati
Affiliations : Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK; Centre for Hybrid and Organic Solar Energy (CHOSE), Department of Electronic Engineering, University of Rome Tor Vergata, Rome 00133, Italy; Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK; Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK; Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK; Centre for Hybrid and Organic Solar Energy (CHOSE), Department of Electronic Engineering, University of Rome Tor Vergata, Rome 00133, Italy; Institute for Materials Discovery, University College London, Torrington Place, London WC1E 7JE, UK; Centre for Hybrid and Organic Solar Energy (CHOSE), Department of Electronic Engineering, University of Rome Tor Vergata, Rome 00133, Italy; Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK; Cavendish Laboratory, University of Cambridge, J.J. Thomson Avenue, Cambridge CB3 0HE, UK; Centre for Hybrid and Organic Solar Energy (CHOSE), Department of Electronic Engineering, University of Rome Tor Vergata, Rome 00133, Italy; Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK; Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK

Resume : The performance of perovskite solar cells (PSCs) has improved fast due to careful optimisation of the perovskite and charge transport layers (CTLs). However, little attention has been paid to the substrate. Almost all non-flexible thin film photovoltaics rely on soda lime glass (SLG), which contains alkali ions such as Na+, Mg2+, and Ca2+. Of these, Na+ is the most likely to diffuse into the device?s active layers due to its small radius and low charge. This is especially true in large-area perovskite solar modules (PSMs) which use the P1-P2-P3 monolithic interconnection because in the P1 lines, the bottom CTL is in direct contact with SLG. Previous studies on deliberate Na doping of PSCs have found a variety of beneficial effects, but also detrimental ones when the concentration of Na is too high. Therefore, studying the extent and potential effects of inadvertent Na diffusion from SLG in PSMs is of great interest to maximise their efficiency and operational stability. In this work, we used a series of spectroscopy and microscopy techniques to study Na diffusion in PSMs with a perovskite stoichiometry of Cs0.05(CH3NH3)0.14(CH(NH2)2)0.81PbI2.7Br0.3. We first used XRD to compare the crystallography of perovskite films deposited on SLG and quartz and found that the perovskite peaks of SLG samples are shifted to lower angles, indicating wider lattice plane spacings. Then, we examined the perovskite grain morphology with SEM imaging and observed Brownian tree-shaped areas (trees) growing perpendicularly from the edges of P1 lines up to ~250 ?m into the active area. While the bulk of the film contains plenty of plate-shaped grains on top of the equiaxed perovskite grains, very few of these plates are found inside the trees. Using AFM, KPFM, and cathodoluminescence (CL) mapping, we deduced that these plates are excess PbI2 from the perovskite precursor solution. Furthermore, CL also shows that near the P1 lines, the perovskite?s luminescence is redshifted by 19 meV and stronger by 6-7x, indicating far less non-radiative recombination. The Brownian tree shape of these PbI2-less areas strongly suggests that their formation was controlled by diffusion from the P1 lines, with Na being the most likely diffusant. We confirmed this by performing cross-sectional elemental mapping with STEM-EDX, through which we obtained direct evidence that Na diffused both vertically (from SLG to CTL/perovskite inside P1 lines) and laterally (from P1 lines into active areas). We found strong correlation between Na and Br in the elemental maps, indicating formation of NaBr inside the perovskite. A mechanism can thus be proposed to explain these observations. Annealing of the CTL/perovskite layers provided enough energy for Na to diffuse from SLG. In the perovskite layer close to P1 lines, Na bonds with Br, leaving the perovskite precursor Br-poor. To compensate, more PbI2 precursor reacted to form I-rich, Br-poor perovskite which explains the XRD and CL peak shifts. The formed NaBr then boosts the perovskite?s local emission by passivating electronic trap sites.

Authors : D. K. Gorai, T. K. Kundu
Affiliations : Indian Institute of Technology Kharagpur, Kharagpur, WB, India-721302

Resume : Graphitic carbon nitride (g-C3N4) shows the excellent possibility to enhance its visible-light photocatalytic performance by tuning its electronic and optical properties as well as bandgap via Li and P co-doping. The Li and P co-doped g-C3N4 is synthesized by the polymerization of melamine, lithium carbonate, and ammonium phosphate at elevated temperature and characterized the obtained sample. After Li and P co-doping, the photocatalytic performance of g-C3N4 for rhodamine B (RhB) and methyl blue (MB) degradation increases by increasing visible light absorption and decreasing the bandgap compared to the pristine g-C3N4. Theoretical results show that after co-doping with Li and P, there is a stronger delocalized HOMO and LUMO state and the reactive sites, which facilitate the migration of photogenerated charge carriers and hence enhanced the photocatalytic performance compared to the pristine g-C3N4. Keywords: Graphitic carbon nitride, codoping, Photocatalysis, rhodamine B, methyl blue, HOMO

Authors : Mriganka Singh, Yu-Jung Lu, and Chih Wei Chu
Affiliations : Mriganka Singh, Yu-Jung Lu, and Chih Wei Chu: Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

Resume : Metal oxide charge carrier transporting materials have been incorporated in many ways in perovskite solar cells (PSCs) because of their excellent chemical stability, wide band gaps, and reasonable mobilities. Herein, we report a low-temperature solution-processed intercalation method for introducing metal oxides displaying bipolar transporting capability into PSCs. We intercalated p-type nickel oxide (NiO) with cesium carbonate (Cs2CO3) to function as hole and electron transport layers for inverted (p?i?n) and conventional planar (n?i?p) PSCs, respectively. When compared with the corresponding NiO-only hole transporting layer, the Cs2CO3-intercalated NiO layer displayed enhanced electron extraction without sacrificing its hole extraction capability. The power conversion efficiencies of the inverted and conventional planar PSCs reached as high as 12.08 and 13.98%, respectively. This approach not only realizes the bipolar extraction capacity of Cs2CO3-intercalated p-type metal oxides but also opens up a possible route for preparing interconnecting layers for tandem optoelectronics. Keywords: Nickel Oxide, Energy Materials, Perovskite Photovoltaics.

Authors : Krol Igor Mikhailovich Barinova Olga Pavlovna Zykova Marina Pavlovna
Affiliations : D. Mendeleev University of Chemical Technology of Russia

Resume : Glasses and glass ceramics doped with transition metal ions are widely used as optical elements of laser devices. Transparent (monocrystalline, glassy, glass-crystalline) materials with cobalt ions are used as a Q-switch of IR lasers generating nanosecond pulses in the range of 1.3 - 1.7 ?m. Cobalt can have either II or III valence and either tetrahedral or octahedral coordination geometry. Due to the presence of a wide absorption band in the 1.3 - 1.7 ?m region tetrahedral coordinated Co(II) is of interest to the Q-switch IR lasers. To create a transparent glass-ceramic material, we chose the ZnO-B2O3-SiO2 system in the region of the eutectic composition. Our choice was motivated by this system?s wide glass transition region and its low melting point. Low-melting glasses obtained in this system can be used to produce glass ceramics with a crystalline phase of zinc silicate Zn2SiO4. During Zn2SiO4 doping the cobalt ion occupies tetracoordinated positions, replacing zinc. We obtained initial transparent glasses of the composition (70-x)ZnO-10SiO2-(20 + x)B2O3 (x = 0; 5; 10) wt. %, doped with cobalt (0.06 wt.% CoO), at a temperature of 1150 °? in corundum crucibles. The phase composition and the dependence of the optical characteristics on the ZnO/B2O3 ratio has been investigated for these glasses. To obtain glass ceramics the glasses were modified by heat treatment. The main crystalline phases have been determined. The influence of the ZnO/B2O3 ratio and the heat treatment mode on the spectral characteristics of the glass-ceramics under study has been established. The IR absorption spectra analysis of the glass ceramics showed the presence of a broad absorption band in the 1.3 - 1.7 ?m region. This band corresponds to the 4A2 ? 4T (4F) transition, which indicates the presence of tetrahedral coordinated cobalt. This shows that glass ceramics are promising in the ZnO-B2O3-SiO2:Co2+ system for passive Q-switches. This work was financially supported by the Ministry of Science and Higher Education of the Russian Federation within the framework of the FSSM-2020-0005 project.

Authors : Vytautas Kavaliunas,1,3,z Yoshinori Hatanaka,2,? Yoichiro Neo,2 Giedrius Laukaitis,3 Hidenori Mimura,2
Affiliations : 1 Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8011, Japan 2 Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, Shizuoka 432-8011, Japan 3 Department of Physics, Faculty of Mathematics and Natural Sciences, Kaunas University of Technology, Studentu str. 50, Kaunas, Lithuania

Resume : The hybrid solar cell technology is a feasible way to improve charge carrier generation through wider spectral selectivity. The conduction band discontinuity affects the properties of such a system. Thus, it is important to design conduction bands throughout the system for charge carrier transfer. This work focuses on p/n junction Si and TiO2 hybrid solar cell design and manufacturing. The TiO2 thin film deposited on p/n junction Si solar cell was modified and analyzed in this work. 6-steps process was used to manufacture layered Si substrate (n++/p++/n+/n++, where n+ ND= 1015-16 cm-3; n++-Si ND= 1020-21 cm-3; p++-Si NA=1019-20 cm-3). TiO2 thin films of ~700nm thickness were deposited on top by a spin-coating technique using a commercially available ?STS-21? solution. The samples were preannealed at 150 °C for 30 min and annealed at 800 °C for 1 h to achieve a high-quality anatase phase. The deposited TiO2 thin-film shows high transparency under the visible light region (n= 1.62 ), which is an important factor for hybrid solar cells. The high porosity (P= 69.63%.) of TiO2 thin films is one of the main defects controlling the surface reactivity and charge transfer. The conduction band discontinuity analysis for n-Si and TiO2 heterojunction was done using XPS measurements. Modifications for the conduction band in the n-Si/TiO2 heterojunction was done by doping the n-Si. The I-V measurements were used to analyze the heterojunction and charge transfer.

Authors : Bich Phuong Nguyen, Hye Ri Jung, Ji Huyn Kim, and William Jo*
Affiliations : Department of Physics, Ewha Womans University, 120-750, Seoul, Korea

Resume : Even though the record efficiency of perovskite solar cells already achieved PCE higher than 25%, one concern with this material is the toxicity of lead leading to a challenge for replacement to Sn, Ge, or Bi. Vexingly, the non-lead materials have drawbacks of low Voc, which is much smaller than the bandgap. In this study, tin-based perovskite material (MASnI3 and MASnBr3) (MA = CH3NH3) using as the light absorber. It is found that the morphology and charge transport of tin-based perovskite depend on the interface of perovskite and electron transport layer. We improved the open-circuit voltage and the photo-current by monitoring the surface by by Kelvin probe force microscopy and conductive-atomic force microscopy, respectively. The surface of the tin-perovskites was tailored by chlorine-passivation. Finally, we achieved PCE higher than 10% of the tin-based perovskites.

Authors : Shivani Shisodia(1), Bénoit Escorne(2), Dharmendra P. Singh(3), A. Hadj Sahraoui(1), Michael Depriester(1).
Affiliations : 1. UDSMM, EA 4476, Université du Littoral Côté d?Opale, 59140 Dunkerque, France, 2. EMLM, ULCO, 145 avenue Maurice Schumann, Dunkerque 59140, France. 3. UDSMM, EA 4476, Université du Littoral Côté d?Opale, Centre Universitaire de la Mi-Voix, 62228 Calais, France.

Resume : The depletion of fossil fuels and increasing energy demand urges us to shift towards renewable and green energy sources. Also, a large part of the consumed energy is dissipated in form of the heat[1]. Therefore, it is necessary to harvest the waste thermal energy to provide a cost-effective and sustainable energy source. Thermoelectric (TE) materials are well-known for their exceptional ability to convert thermal energy into electrical energy and vice versa[2]. However, the interdependence of thermal and electrical conductivities makes it difficult to achieve a high thermoelectric figure of merit. Hybrid organic-inorganic materials have drawn much attention in thermoelectric applications due to the low thermal conductivity of organic parts and high electrical conductivity of the inorganic counterparts[3]. In the present work, inorganic Graphene Oxide - titanium dioxide (GO-TiO2) nanocomposite has been incorporated into an organic Poly (3,4-ethylene dioxythiophene)-(PEDOT) and poly(styrene sulfonate)- PSS polymer matrix. Different composites of the GO-TiO2@PEDOT: PSS were synthesized by the sol-gel method and their thermoelectric performances near room temperature have been examined. The thermal conductivity of the hybrid polymer is found to be decreased with the addition of GO-TiO2 fillers. A parallel enhancement in the Seebeck coefficient was observed due to an advantageous contribution of the GO-TiO2 on the effective Seebeck coefficient. Mixture laws will be used to model the effect of filler loading concentration on these parameters. Insights will be obtained from these first investigations to improve these composites. References: [1] Clemens Forman et al., vol 57, page 1568-1579, Renewable and sustainable energy reviews, 2016. [2] Orr B, Akbarzadeh A.vol 110, page 250-255, Energy Procedia 2017. [3] Xu Q et al., vol 12, page 13371-77, ACS Appl Mater Interfaces 2020.

Authors : Mariusz Radtke, Christian Hess
Affiliations : Technical University of Darmstadt, Germany

Resume : As the energy production becomes less of a bottleneck, its storage is still not fully understood. For example the changes occurring at the molecular level are challenging to grasp by integral techniques of pure electrochemistry, therefore the use of operando spectroelectrochemistry becomes an asset. Raman spectroelectrochemistry for example provides information about changes in the vibrational structure of the molecules at and in some cases (tip enhanced Raman spectroscopy) below the diffraction limit. As many materials used in e.g. Li-ion batteries (LIB) are challenging in spectroscopic investigations due to the small Raman cross-section, surface enhanced spectroscopy is a tool to overcome this obstacle. We present a methodology towards investigation of mechanisms underlying the energy storage in LIB. A precise coupling of Potentio-Electrochemical-Impedance-Spectroscopy (PEIS) with Surface-Enhanced-Raman-Spectroscopy (SERS) allows for distinguishing between the movements of specific ions in delithiation processes and indicates a surprising fact of e.g. carbon being involved in the overall mechanism. The charge transfer mechanisms and mass-transport properties (intercalationof lithium) can be monitored in time and the kinetics of each reaction/movement investigated in-time (Fig. 1). Raman shifts were found to follow the applied potential and the skin-depth resolved investigation in transition state metallic states of RedOx reactions was made possible. We also present the perspective results about the coupling of Raman Spectroelectrochemistry to Operando X-Ray-Photoelectron-Spectroscopy (XPS) for direct insights into changes of both vibrational and electronic structure during the battery's operation. References: M. Radtke, C. Hess Operando Raman shift replaces current in Butler-Volmer analysis of Li-ion batteries: a comparative study (submitted) M. Radtke, C Hess Surface Enhanced Raman Spectroscopy Substrates for Use in Operando Raman Spectroelectrochemistry (in preparation)

Authors : Yu-Ting Chen
Affiliations : Jyh-Ming Wu

Resume : Lithium-ion batteries (LIBs) have been considered the most promising energy storage system candidates for electric vehicles (EVs). However, LIBs are facing two significant challenges: cost and safety. First, LIBs are the main factor in the high price of EVs. LIBs are estimated to account for 30-50% of the cost of EVs. The high manufacturing cost of EVs makes them non-affordable for everyone. Second, organic solvents were utilized as liquid electrolytes in LIBs, which have safety issues such as flammability and leakage that become critical to address it. Moreover, dendrites formation in liquid electrolyte batteries, thus causing thermal runaway risk. All-solid-state batteries (ASSBs) are considered a promising technology due to high safety, high stability, and a low thermal runaway risk. The most critical component of ASSBs is solid electrolytes. The solid composite electrolytes (SCEs) constructed by polymer matrix and inorganic fillers inherit both advantages, such as high ionic conductivity, good flexibility, and intimate contact with electrodes. Therefore, SCEs are regarded as potential solid electrolytes for ASSBs. The highly porous SiO2 particles (HPSPs) were utilized as the inorganic fillers to increase ionic conductivity, thermal stability and suppress dendrite formation. The HPSPs were mixed with PEO matrix and lithium salt to obtain HPSPSCEs. Finally, the HPSPSCEs were assembled into CR2032 coin batteries to measure various electrical properties. The ionic conductivity of HPSPSCEs at room temperature is enhanced by one order of magnitude by adding 5 wt.% of the HPSPs. Besides, this work combines experimental data and computational simulation. The simulation results implied that the fillers have the optimal amount of addition, consistent with the experimental data. Moreover, through the galvanostatic cycling at C/10, the specific capacity could still maintain 94% after 150 cycles, which demonstrated excellent stability. Besides, adding the HPSPs also reduced the risk of battery thermal runaway. In the fire resistance test, the HPSPSCEs were burned by fire and measured their resistance time. The HPSP fillers could effectively prolong the burning time to 175% which compared with pure PEO. More importantly, the HPSPs were recycled from nature, which are much more ecofriendly, sustainable than those fillers commonly used in SCEs such as commercial SiO2, almost no cost. This research provides another possibility for developing affordable, sustainable, effective, and safe LIBs in the future.

Authors : Sheng-Ruei Jhang, Jyh Ming Wu
Affiliations : Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan

Resume : This work demonstrates a core-shell PTFE (polytetrafluoroethylene) and TiO2 catalyst, which exhibits degradation activity highly based on synergistic photocatalysis and strain-induced piezoelectric effect. The X-ray diffractometry (XRD) and Raman spectra showed the interfacial strain between PTFE and TiO2, while the piezoresponse force microscopy (PFM) showed a piezo response amplitude (PRA) of 8mV, which clearly indicated the piezoelectricity of strained PTFE. Rhodamine B was wholly decomposed in 20 minutes under ultrasonication and light irradiation, with the pseudo-first-order rate constant (kobs) of 0.122 (min-1) over three times higher than sole light irradiation. The highly decomposed activity is ascribed to the synergistic effect of photocatalysis and interfacial strain-induced piezocatalytic effect. The electron paramagnetic resonance (EPR) and fluorescence spectroscopy were used to investigate the reactive oxygen species. In addition, Kelvin probe force microscopy (KPFM) showed the work functions of PTFE and TiO2 to be 5.75eV and 4.2eV, which revealed a significant difference of 1.55eV. During contacts and separations under the ultrasonic environment, a considerable number of surface electrons was thus transferred from TiO2 to PTFE. The above instrumental analyses suggest that strain engineering and difference of work functions together play a dual role in the enhancement of piezocatalytic effect, leading to the formation of hydroxyl radical species, which is the most significant component in decomposition of dye molecules.

Authors : Solis-De la Fuente, M. (1), Márquez-García, L. (1), Castro-Ruiz, S. (1) Beltrán-Pitarch, B. (1), García-Cañadas, J. *(1).
Affiliations : (1) Universitat Jaume I, Departamento de Ingeniería de Sistemas Industriales y Diseño, Av. Vicent Sos Baynat s/n, 12006 Castelló de la Plana, Spain * lead presenter

Resume : Thermoelectric (TE) technology for energy harvesting remains limited by its low efficiency. One of the main obstacles to achieve more efficient materials is the adverse correlation between the Seebeck coefficient S and the electrical conductivity σ. We have recently introduced a radically new concept in thermoelectricity that has demonstrated large improvements (more than 3 times) in the power factor (PF=S2σ).1 The concept is based on a hybrid system where a porous nanostructured TE material is impregnated by an electrolyte (liquid with ions). The electrolyte fills the pores and the TE properties of the solid can be significantly improved. The concept has been demonstrated in SnO2 doped with Sb in contact with different electrolytes.1 Here we show higher PF improvements in the same material (Sb:SnO2) when it is contacted by other different electrolytes. The improvements are achieved by breaking the adverse S-σ interdependence, leading to remarkable PF improvements. These improvements open the possibility to apply this approach to materials with better initial TE properties than Sb:SnO2, which could potentially lead to huge TE efficiencies, which is the aim of the European UncorrelaTEd project.2 References 1. L. Márquez-García, B. Beltrán-Pitarch, D. Powell, G. Min and J. García-Cañadas. Large power factor improvement in a novel solid-liquid thermoelectric hybrid device. ACS Applied Energy Materials 1, 254-259 (2018). 2.

Authors : (1) S.Guehairia, R. Demoulin, P. Pareige, E. Talbot, (2) F. Gourbilleau, J. Cardin, C. Labbé, (3) M. Carrada
Affiliations : (1) Normandie Univ, UNIROUEN, INSA Rouen, CNRS, Groupe de Physique des Matériaux, 76000 Rouen, France (2) CIMAP, Normandie Univ, ENSICAEN, UNICAEN, CEA, CNRS, CIMAP, 14000, Caen, France (3) CEMES-CNRS, Université de Toulouse, 29 rue Jeanne Marvig, BP 94347, F-31055 Toulouse, France

Resume : Rare-earth (RE) -doped Si-based matrix [1-2] have attracted a lot of attention due to their many potential applications in photonics [3]. Light emission properties exhibited by RE are directly linked to their distribution with respect to the Si-nanoscale sensitizers as well as the clustering characteristics (size, distribution, composition, interface nature with surrounding matrix?) [4]. Therefore, an accurate control of these parameters is essential in order to improve the optical properties of these systems. However, the solubility of rare earth ions in Si-based matrix remains still relatively low and most of the RE ions are optically inactive at high concentration due to the formation of cluster [5]. In present work, we have studied the structural and optical properties of highly doped Er silica layer at atomic scale. These investigations have been performed using photo- and cathodo-luminescence, transmission electron microscopy and atom probe tomography. The influence of Erbium concentration and annealing process have been studied. We show that erbium distribution atoms as well as phases formation depends on the erbium concentration and annealing conditions (RTA or conventional). Indeed, we have the formation of the stable erbium silicate phase Er2Si2O7 with a finer structure like to honeycomb in the case of conventional annealing and a more important coalescence with rapid annealing. It results in a higher emission intensity in this later whether in the ultraviolet or infrared range. The relationship between structural and optical properties will be discussed. [1] Kenyon, A. J. « Erbium in silicon ». Semiconductor Science and Technology, vol. 20, n? 12, décembre 2005, p. R65?84. Doi:10.1088/0268-1242/20/12/R02. [2] Das, Debajyoti, et Arup Samanta. « Quantum Size Effects on the Optical Properties of Nc-Si QDs Embedded in an a-SiO x Matrix Synthesized by Spontaneous Plasma Processing ». Physical Chemistry Chemical Physics, vol. 17, n? 7, 2015, p. 5063?71. Doi:10.1039/C4CP05126B. [3] Daldosso, N., et L. Pavesi. « LOW-DIMENSIONAL SILICON AS A PHOTONIC MATERIAL ». Nanosilicon, Elsevier, 2008, p. 314?34. Doi:10.1016/B978-008044528-1.50010-5. [4] Fujii, Minoru, et al. « Photoluminescence from SiO2 Films Containing Si Nanocrystals and Er: Effects of Nanocrystalline Size on the Photoluminescence Efficiency of Er3+ ». Journal of Applied Physics, vol. 84, n? 8, octobre 1998, p. 4525?31. Doi:10.1063/1.368678. [5] Beainy, Georges. Etude structurale et optique de la précipitation des ions de terres-rares et des nanoparticules de silicium dans la silice pour des applications optiques. Normandie Université, France, 3 novembre 2016.

Authors : Candida Pipitone (1), Francesco Giannici (1), Antonino Martorana (1), Antonietta Guagliardi (2), Gonzalo García-Espejo (3), Norberto Masciocchi (3)
Affiliations : (1) Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, viale delle Scienze Ed. 17, 90128 Palermo, Italy; (2) Istituto di Cristallografia & To.Sca.Lab., Consiglio Nazionale delle Ricerche, via Valleggio 11, 22100 Como, Italy; (3) Dipartimento di Scienza e Alta Tecnologia & To.Sca.Lab., Università dell?Insubria, via Valleggio 11, 22100 Como, Italy

Resume : Organic-inorganic halide perovskites and pseudo-perovskites have gained a growing interest in the last decade, for diverse applications as photovoltaics, solar thermoelectrics, light emitting diodes and laser. The most studied compound is (CH3NH3)PbX3 (X= I, Br, Cl), where corner sharing [PbX6] octahedra form a 3D inorganic scaffold containing the organic moieties. Even if their properties are promising, these compounds still do not meet the requirements to find real application in working devices, and there are also concerns about their stability. With the aim of extending the library of such compounds, different organic cations have also been introduced in the perovskite framework, leading to different connectivity between lead halide octahedra and different dimensionality of the scaffold, from 2D to 0D. These lower-dimensional pseudo-perovskites feature a useful structural flexibility that can be further exploited in order to optimize the electronic properties, and eventually enhance the stability of these materials. There is plenty of room for further exploration of the interplay between structure and properties of these compounds. For this reason, we prepared hybrid low-dimensional iodide pseudo-perovskites, employing lead and bismuth as B site cation and trimethylsulfoxonium ((CH3)3SO+, TMSO) in the A site, by precipitation from aqueous HI. To characterize these samples, structural, thermal and optical absorption studies were performed (X-ray diffraction, TGA, SEM and UV-vis reflectance). Pure Pb- and Bi-end members show complete miscibility in the solid state, so that (TMSO)3Pb3xBi2(1-x)I9 samples, with x ranging from 0.99 to 0.33, were successfully synthetized and do not show any segregation. Interestingly, XRD measurements heavily suggest a ionic defectivity on the B site as major charge compensation mechanism, with a Pb2+ vacancy every other two Bi3+ doped sites. The influence of bismuth doping on the optical properties is significant: even a low loading of bismuth in the structure decreases the band gap of about 0.5 eV. This work is a first insight on the effect on both structure and properties of inorganic cation doping on a 1D hybrid pseudo perovskite structure.

Authors : Yao Adaba, Laurent Castro, Phillipe Poizot, Stéven Renault
Affiliations : Yao Adaba (Université de Nantes, Institut des Materiaux Jean Rouxel, IMN, F-44000 Nantes, France); Laurent Castro (TME-Toyota Motor Europe NV / SA, Research & Developpement 1, Hoge Wei 33 A, B-1930 Zaventem, Belgium); Philippe Poizot (Université de Nantes, Institut des Materiaux Jean Rouxel, IMN, F-44000 Nantes, France); Stéven Renault (Université de Nantes, Institut des Materiaux Jean Rouxel, IMN, F-44000 Nantes, France)

Resume : As the world moves toward electromobility and a concomitant decarbonization of its electrical supply, modern society is also entering a so-called fourth industrial revolution marked by a boom of electronic devices and digital technologies. Consequently, battery demand has exploded. Introduced on the market in 1991, lithium-ion batteries (LIBs) is becoming a flagship technology possibly able to power an increasingly diverse range of applications from microchips to the emerging large-scale application markets of electric vehicles. However, their energy density is still too low for long range applications especially per unit of volume, as compared to internal combustion engines. In order to surpass the performances offered by current LIBs, the chemistries based on the Li-O2 couple in aprotic electrolyte seem promising to really provide ultrahigh-energy density values. The main targeted application is the powering of electrified vehicles with the hope of achieving a reasonable driving range (typically more than 550 km before charging, ca. 340 miles). A typical design for aprotic Li-O2 batteries is composed of a negative electrode made of metallic lithium, an electrolyte comprising a dissolved lithium salt in an aprotic solvent, a separator (e.g., glass fiber or a Celgard film), and a porous O2-breathing positive electrode composed of black carbon particles often blended with catalyst particles. Li-O2 batteries could, in principle, double the gravimetric energy density over the current Li-ion technology, but serious side-reaction issues have plagued their development for practical applications. For example, during the discharge process, some undesired insulating products are formed instead of lithium peroxide. Moreover, the blocking/clogging effect on the air electrode due to a selected deposition process leads to an overpotential during both the discharge (Oxygen Reduction Reaction: ORR) and charge processes (Oxygen Evolution Reaction: OER), which results in electrode degradation, electrolyte decomposition and precocious cell death. Another striking point is that reported capacities are often lower than those expected based on the available porosity. The aim of this work is to use commercial polycyclics aromatics hydrocarbons (PAH) such as pyrene, perylene and coronene as additives in the fabrication of the porous carbonaceous positive electrode. Their solubility in the liquid electrolyte system creates new accessible surface areas in the air electrode, which improved the performance of the Li-O2 batteries.

Authors : Jiewen Wei, Prof. Saif Haque, and Dr. Thomas Macdonald
Affiliations : Department of Chemistry, Imperial College, London

Resume : Perovskite nanomaterials have attracted extensive attention in recent decade owing to their high photoluminescence quantum yield, narrow emission spectrum, high colour purity, and emission wavelength tunable across the entire visible spectrum. Therefore, perovskite nanomaterials are promising candidates for next-generation solid-state lighting sources. It is well known that the surface ligands play an important role in the synthesis of perovskite nanocrystals, which can control the size and stability of nanocrystals. Nevertheless, the effect of surface ligands on the interfacial charge transport in perovskite nanocrystals light-emitting didoes architecture remains poorly understood. In my contribution, I will systematically investigate the ligand effects on interfacial hole transport by tuning the hydrophobicity of passivating ligands used in nanocrystals synthesis. These results provide insights into the control and optimization of interfacial charge transfer processes for efficient perovskite nanocrystals LEDs.

Authors : Htet Su Wai, Chaoyang Li
Affiliations : Kochi University of Technology; School of Systems Engineering

Resume : Zinc oxide (ZnO) thin films are the attractive for the antiviral applications due to their excellent photocatalytic properties which can produce high reactive oxygen species.1 However, ZnO film has high recombination rate of electron-hole pairs and it can interrupt the photocatalytic effects of ZnO. Therefore, an alternative solution is to dope aluminum into ZnO films because it can reduce the recombination rate of electron-hole pairs and increase the photocatalytic effects of ZnO. In this research, both non-doped ZnO film and aluminum-doped ZnO (AZO) film were deposited by chemical vapor deposition method, the structural and photocatalytical property were investigated. There are two kinds of solutions were prepared for synthesizing ZnO and AZO film individually. (1) ZnO film: zinc acetate (0.04 mol/L) was dissolved in the mixed solution of methanol and water. (2) AZO film: a solution of mixed precursor was prepared by dissolving of aluminum acetyl acetate with different concentration (0~10%) and zinc acetate (0.04 mol/L). The mist was produced from solution chamber by ultrasonic generator, then N2 gas was severed as carried gas and dilution gas, the reaction was occurred in fine-channel reaction chamber at 400?C The thickness, solvent concentration and the annealing effects on the structural and photocatalytic property were evaluated by SEM, XRD, and UV-Vis-IR spectrometer. As a result, SEM images of pure ZnO films with different thickness were observed with wedge-like structures and uniformity. The average grain sizes of ZnO film was increased with the thickness increasing. The XRD results showed that the dominated peak for all film was (002) peak which was corresponding to the c-axis orientation growth during mist CVD process. The optical transmission spectra of all films were greater than 60% in the visible region. After thermal annealing process, the average grain size of ZnO films was gradually increased from 150 to 220 nm with the thickness increasing. Comparing to as-deposited films, the crystallinity was significantly increased and the transmittance of all ZnO films was around 90%. Therefore, the post-annealing method was efficiently to improve the crystallinity and transmittance of ZnO films. The photocatalytic activity will be measured for both of ZnO and AZO films, the photocatalytic degradation results will be reported and the mechanism will be revealed. References, [1] Yamamoto O. Influence of particle size on the antibacterial activity of zinc oxide. Int. J. Inore Mater. (2013). 643-646.

Authors : Debosmita Banerjee, Kamatchi Jothiramalingam Sankaran, Sujit Deshmukh, Mateusz Ficek, Chien-Jui Yeh, Jacek Ryl, I-Nan Lin, Robert Bogdanowicz, Aloke Kanjilal, Ken Haenen, Susanta Sinha Roy
Affiliations : Department of Physics, School of Natural Sciences, Shiv Nadar University, NH-91, Gautam Buddha Nagar, Uttar Pradesh 201314, India; Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium; Department of Physics, School of Natural Sciences, Shiv Nadar University, NH-91, Gautam Buddha Nagar, Uttar Pradesh 201314, India; Department of Metrology and Optoelectronics, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, 11/12 G. Narutowicza St., 80-233 Gdansk, Poland; Department of Physics, Tamkang University, Tamsui, 251 Taiwan, Republic of China; Department of Electrochemistry, Corrosion and Materials Engineering, Faculty of Chemistry, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland; Department of Physics, Tamkang University, Tamsui, 251 Taiwan, Republic of China; Department of Metrology and Optoelectronics, Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, 11/12 G. Narutowicza St., 80-233 Gdansk, Poland; Department of Physics, School of Natural Sciences, Shiv Nadar University, NH-91, Gautam Buddha Nagar, Uttar Pradesh 201314, India; Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium; Department of Physics, School of Natural Sciences, Shiv Nadar University, NH-91, Gautam Buddha Nagar, Uttar Pradesh 201314, India

Resume : Over the last few decades, designing efficient electrode materials has been of immense importance to satisfy the need for miniaturized portable energy storage equipments. Recently, integration of multiple carbon allotropes in a single hybrid nanostructure has garnered attention because of their synergistic composite physical and electronic behaviour. In the present work, a repeatable, single-step synthesis of a unique carbon hybrid consisting of carbon nanograsses (CNGs) over boron doped nanocrystalline diamond (BNCD) has been demonstrated by using a microwave plasma enhanced chemical vapour deposition technique. The newly designed material has been further evaluated as electrodes for electrochemical supercapacitor in both inert electrolyte and redox pair contained electrolyte. A specific capacitance value of 0.4 F/cm2 was achieved in redox-active electrolyte, with a remarkable stability of 95% even after 10000 charge-discharge cycles. Rigorous material characterizations along with electrochemical characterizations were performed which suggest that the hybrid combines the dual advantages of sp2-carbon (CNG) with excellent electrical characteristics and sp3-carbon (BNCD) with exceptional electrochemical stability. Moreover, the one-dimensional grass-like structure provides larger surface area facilitating the charge transfer kinetics. This study could certainly widen the scope and freedom of new hybrid diamond materials being implemented for future energy storage devices.

Authors : Jiaxin Pan, Weidong Xu, Dr Artem Bakulin, Dr Piers Barnes
Affiliations : Imperial College London

Resume : A new optical Pump-Push-Photocurrent (PPP) technique is built up to study the carrier dynamic in the perovskite Photovoltaic Solar Cells (PSCs). Perovskite PSCs have attracted scientists? attention in recent decades, due to the high- power conversion efficiency (PCE) and potentially low cost of manufacturing. However, the charge trapping and associated recombination processes negatively affect perovskite device performance. Particularly we are interested in the kinetics of charge trapping and nonradiative recombination in the device active layer. We have performed quasi-steady-state measurements of device performance under simultaneous illumination by visible and IR laser diode. The preliminary results show that the effect of IR push light scales linearly with IR light intensity but depends in a more complex way from the intensity of visible light. By measuring the induced photocurrent as a function of light-modulation frequency we have performed an estimation of carrier lifetime. Moreover, the temperature-dependent current density measurements show that the effect of IR light on the device performance does not originate from the sample heating but likely leads to the carrier detrapping.

Authors : Sarah Su-O Youn [1,2], Un Go [2], William Jo [1], Gee Yeong Kim [2]
Affiliations : [1] Department of Physics, Ewha Womans University, Seoul, 03760, Korea [2] Advanced Photovoltaics Research Center, Korea Institute of Science and Technology, Seoul, 02456, Korea

Resume : Hybrid lead halide perovskite is one of the promising photovoltaic materials due to its high efficiency and interesting scientific aspects. Methylammonium lead iodide (MAPI), unlike other photovoltaic materials, is a mixed electronic and ionic conductor and has high ionic charge carrier concentration [1]. Previous study shows that in MAPI/TiO2, ions are responsible for the equilibrium space charge potential due to ion adsorption at the contact area between MAPI and oxide layers [2]. Meanwhile, the replacement of conventional TiO2 electron transport layer with SnO2 has been applied and SnO2 proves to be useful in devices due to low-temperature process and high electronic mobility. However, the interfacial effect on charge transport between SnO2 and perovskite is not clearly identified. To investigate the interfacial effect in SnO2, we observed the adsorption behavior of SnO2 nanoparticles in MAPI:SnO2 composite and compared it to TiO2. We also provided a comparison between compact SnO2 layer (prepared by ALD) and composite layer (prepared by spin coating). In order to understand the charger transport properties, we investigated the electrical conductivity in MAPI/SnO2 thin films by controlling the contact area between MAPI and SnO2. Moreover, we studied how the interface effect contributes to charge extraction and recombination in perovskite solar cells. This work will provide a better understanding of perovskite solar cells and a new insight to interface engineering. [1] A. Senocrate, I. Moudrakovski, G. Y. Kim, T. ?Y. Yang, G. Gregori, M. Graetzel, and J. Maier, Angew. Chem.Int. Ed, 56 (2017) 7755-7759. [2] G. Y. Kim, A. Senocrate, D. Moia, and J. Maier, Adv. Funct. Mater,30 (2020) 2002426.

Authors : Ana L. Pires1, João Magalhães2, Margarida Maia1, Clara Pereira3, Reyes Mallada4, María P. Pina4, and André M. Pereira1
Affiliations : 1 IFIMUP, Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Porto, 4169-007, Portugal 2 InanoEnergy, Edifício FC6, Rua do Campo Alegre 1021, Porto, Portugal 3 REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Porto, 4169-007, Portugal 4 INMA, Instituto de Nanociencia y Materiales de Aragón, CSIC-Universidad de Zaragoza. Departamento de Ingeniería Química y Tecnologías del Medio Ambiente, C/Mariano Esquillor, s/n, 50018 Zaragoza, Spain.

Resume : Thermoelectric generators (TEGs) are envisioned as energy converters for powering specific devices in remote locations. Their potential deployment is particularly advantageous in places with insufficient illumination levels and without access to an electric plug but presenting sufficient heat release. Thus, TEGs would allow wireless powering towards autonomous sensors. The phenomenon relies on the Seebeck effect, which consists of the direct waste heat conversion into electrical energy. The figure-of-merit to evaluate the thermoelectric (TE) materials performance is the ZT factor, where ZT=PF/k, and PF is the power factor defined as PF=S^2×? (k, thermal conductivity; S, Seebeck coefficient; and ?, electrical conductivity) [1]. Flexible TEGs are an emerging technology in this area, that would allow the production of lightweight and easy implementation devices. Moreover, the techniques to produce these flexible devices are based on printing methods that can be easily scalable. Despite the extensive effort on TEGs, the energy transfer efficiency of commercial rigid TEGs is less than 5% and becomes even lower in flexible TEGs. Such low conversion arises from the composition of printable inks. Besides being in the majority constituted by the inorganic TE material, the ink formulation contains additional components, such as the polymer binder and other additives to get high mechanical performance that can compromise the TEG performance. Several approaches are being studied to find a trade-off, i.e., incorporation of conductive nanomaterials to establish the electrical pathway between the TE microparticles or by burning the different ink components. In the present work, flexible inorganic-organic printed TE films were prepared by mixing Bi2Te3 microparticles (< 50?m) and poly(vinyl alcohol) (PVA) polymer in different mass ratios (Bi2Te3 wt%) [2]. In particular, the effect of post-annealing on the TE performance of the printed films was fully investigated. Our preliminary results have shown an increase of the ? by using a post-thermal treatment at 200ºC for 1h with N2 as sweep gas. The sample with 20% vol of Bi2Te3/PVA film showed a maximum of ~140 S/m, accounting for 2 orders of magnitude higher than the counterpart prepared without annealing (reaching the electrical conductivity similar to the bulk TE material). Finally, a planar TEG based on the optimized ink and post thermal treatment was prepared and tested. Acknowledgments: Financial support from H2020-MSCA-RISE-2018?823895, PTDC/CTM-TEX/31271/2017, UIDB/04968/2020, UIDB/50006/2020, and NORTE-01-0145-FEDER-022096 from NECL is gratefully acknowledged. ALP, MM and AMP thank the funding from the European Union?s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 863307, Ref. H2020-FETOPEN-2018-2019-2020-01. CP thanks FCT for the FCT Investigator contract IF/ 01080/2015. Refs: [1] Jaziri, N. et al. Energy Reports 7, (2019) [2] Pires, A. L. et al. ACS Appl. Mater. Interfaces 11, (2019)

Authors : L.I. Khirunenko, M.G. Sosnin, A.V. Duvanskii, N.V. Abrosimov, H. Riemann
Affiliations : Institute of Physics, National Academy of Sciences of Ukraine, Prospekt Nauki 46, 03028, Kyiv, Ukraine Leibniz-Institut für Kristallzüchtung, Max-Born Str. 2, D-12489 Berlin, Germany

Resume : Silicon doped with boron (Si:B) is the main material in the manufacture of solar cells. Development of new more efficient converters requires the detailed knowledge of the influence of the boron on the defect-impurities interaction appearing both during the technological stages of cells making and during their operation. We report the new data on the electronic absorption of boron-related defects in monocrystalline silicon. The samples of p-type (boron doped) Si grown by Czochralski and float zone methods were studied. The concentration of boron in samples was varied in the interval (1?2.9)×1016 cm-3 and the oxygen content was ranged from 1.6×1017 to 1×1018 cm-3. A previously unreported absorption line has been detected in the range of intracenter transitions for boron atoms (240-350 cm-1) with maximum at about 261.3 cm-1. Revealed line is located near of the most intense transition from the even-parity 1?8+ ground state to the odd-parity excited state 2?8? of boron atoms (278.3 cm-1) and overlaps with absorption line near 261 cm-1 known as boron-? acceptor. The revealed line is not observed for the oxygen-lean float zone Si samples. The detected line intensity grows with increasing boron and oxygen concentration in samples. This implies that both a boron and oxygen atoms enter the composition of the defect with which the revealed line is associated. Defect responsible for the revealed line forms already during growing of material and the concentration of it increases significantly upon annealing of samples in the temperature range 300-400o C. Compensation of the material with thermal donors forming during heat treatment leads to a decrease in the intensity both the main transitions of boron atoms and the revealed line. This indicates the acceptor nature of the detected defect. The defect anneals in the temperature range of 600-650 ° ?. The model of revealed defect is discussed.

Authors : Shafi Ullah, Amal Bouich, Hanif Ullah, Rahat Ullah, Bernabé Marí.
Affiliations : Institute de Disseny i Fabrication. Universitat Politécnica de Valencia, Camí de Vera s/n, 46022, Valencia, Spain. Electrical Engineering Department, FUUAST Khayaban-e-Suhrwardy 44000, Islamabad, Pakistan.

Resume : Binary tin disulfide (SnS2) is n-type semiconductor material considered a potential candidate with a tunable bandgap used as a buffer layer for CIGS and CZTS solar cells. The Sn1-XVxS2 samples were successfully prepared by solution mixed hydrothermal technique. The crystallographic, morphological, elemental conformation and optical properties were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersion microscopy (EDS), Atomic force microscopy (AFM), UV-Vis spectroscopy and electrochemical analysis, respectively. The XRD analysis revealed the polycrystalline nature of the films. Raman spectroscopy indicated a prominent peak at ~ 315 cm-1 along with two small peaks after the incorporation of V contents. The AFM analysis showed the big grain and the rough surface of the films. The optical absorption indicates a remarkable shift to the lower wavelength and the optical band gap was found to vary from 2.42 to 2.02 eV with V- doped contents. The photocurrents response of the V-doped SnS2 films was conducted by three-electrode configuration which demonstrating good photoresponse, three times higher than pure SnS2 photoanode. The results reveal that the V- doping with SnS2 is a very promising compound for effectively photovoltaic application.

Authors : M. M. Maia1, M. Rocha1, C. Pereira2, A. M. Pereira1
Affiliations : 1 IFIMUP, Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Porto, 4169-007, Portugal; 2 REQUIMTE/LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Porto, 4169-007, Portugal.

Resume : Nowadays, mobility, convenience, and safety of electronic devices are daily concerns. Considering that everyday life small devices have a low-power consumption, the search for simple alternative energy sources is rapidly increasing. Energy Harvesting (EH) technology emerges as an excellent solution for this type of application, hence replacing batteries and providing a long-term power supply1. One of the most significant EH fields is the thermoelectric generators (TEGs), which can convert heat to energy. The vast range of possibilities for these devices has risen great interest from both scientific and industrial communities. The most commonly researched TE materials are the doped semiconductors and semimetals, that have high efficiencies but tend to be too heavy and brittle, with high-cost and complex fabrication2. Consequently, hybrid materials that combine the potentialities of inorganic TE with the light?weightiness, flexibility, and low?cost of organic polymers, arise as an appealing solution. Printing techniques allow the fabrication of TE devices in flexible substrates in a more scalable approach, by combining TE particles and a polymeric binder to form the printable ink. Herein, we present the optimization of highly scalable production of flexible TEGs, based on the screen-printing method. The studied begins with the inks formulated using Bi-Te particles (< 50?m) as the functional TE material and Polyvinyl Alcohol (PVA) as the binder and printed by stencil printing, a technique at the laboratory level3. A Seebeck coefficient of ~150?VK-1 and a Power Factor of 0.1?Wm-1K-2 were obtained. To achieve a more scalable industrial approach, a transition from stencil printing to screen-printing has been developed. Particular emphasis is given to the rheological properties of the developed inks, trying to obtain viscosity values of ~1000Pas by the application of additives while trying to maintain the electrical performance. The risks and applied strategies to optimize the studied TE inks will be presented. The transfer between laboratory and industry offer a nice balance symbiosis and need to be considered in this research area. By employing the screen-printing technique, several advantages arise, such as low-cost, adaptability, and simplicity, with the capacity to have a roll-to-roll industrial production in the future. Acknowledgements: Financial support from PTDC/CTM-TEX/31271/2017, UIDB/04968/2020, UIDB/50006/2020, and NORTE-01-0145-FEDER-022096 from NECL is gratefully acknowledged. MMM, ALP, MR and AMP thank the funding from the European Union?s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 863307 (Ref. H2020-FETOPEN-2018-2019-2020-01). MMM thanks FCT for grant SFRH/BD/144229/2019. CP thanks FCT for the FCT Investigator contract IF/ 01080/2015. References: 1Y. Bai, et al, Advanced Materials. 30 (2018). 2Q. Zhang, et al; Advanced Materials. 26 (2014). 3A.L. Pires et al; ACS Applied Materials & Interfaces. 11 (2019).

Authors : Jihyun Kim(1), Bich Phuong Nguyen(1), Gee Yeong Kim(2), Yeon Soo Kim(1), and William Jo*(1)
Affiliations : (1) Ewha Womans University, Seoul, 03760, Korea; (2) Advanced Photovoltaics Research Center, Korea Institute of Science and Technology, Seoul, Korea

Resume : Highly conducting SnO2 thin films are popular metal oxide semiconductor (MOS) as transparent conducting electrodes for displays and n-type transport layers for perovskite solar cells. The SnO2 thin films are fabricated on the FTO substrates by spin coating and treated with various ozone treatments and then chlorine passivation. In this process, exotic oxygen vacancy states change to the identical conducting states. This study reconstructs the importance of the NH4Cl passivation and UV ozone (UVO) treatment of MOS as electron extraction layers for perovskite photovoltaic applications in the ambient air. NH4Cl passivation SnO2 (np-SnO¬2) can provide that, compared to their untreated films, an improved optical and electrical properties. The morphological, physical properties of the np-SnO2 was confirmed by atomic force microsopy (AFM). Surface facile robust treatment of SnO2, such as UVO treatment, was also applied to SnO2 films before NH4Cl treatments. Spectroscopic and microscopic techniques were conducted to investigate the physical and optoelectronics properties of the samples. The band structure, surface potential and carrier transport mechanism were explained by Kelvin probe force microscopy. Higher current density of np-SnO2 was displayed when compared with UV ozone treated SnO2. The results suggest that the np-SnO2 can serve as a better electron extraction layer to promote charge separation and suppress charge recombination. Therefore, these are beneficial for reducing the recombination of carriers, enhancing of optoelectronics device like a perovskite solar cell performance.

Authors : Lou BERNARD, Alia JOUHARA, Pierre TRAN-VAN, Stéven RENAULT, Philippe POIZOT
Affiliations : Technocentre Renault, Guyancourt, France ; Institut des Matériaux Jean Rouxel, Nantes, France

Resume : Currently, inorganic active materials such as metal oxides or phosphates dominate the field of Li-ion battery electrode materials. However, they stem from mining and their synthesis process around 900°C require an important amount of energy (e.g. 286 kWh for the production of 1 kWh of NMC-based storage capacity). Thus, the environmental footprint of such batteries is not neutral: Global Warming Potential of the aforementioned NMC-based kWh releases in average 160 kgCO2eq. Meeting the ever-growing needs for electrical storage devices while reducing the environmental impact and the demand for unsustainable raw materials call for greener battery technologies. Among the various lines of research, organic redox materials could offer the possibility of rising to those challenges. To date, no Life-Cycle Assessment study proves their environmental footprint is lower than current inorganic materials, but different arguments can be put forward in their favor. As they are composed of naturally abundant chemical elements (in particular C, H, O, N and S), they avoid mining and can lead to low-cost chemistry. More, their syntheses are performed below 100°C and can involve raw materials potentially obtained from renewable resources. Finally, their wide choice of chemical structures and functions for organic molecules offers opportunities to tune their redox potential and promote reversible multielectron reactions demonstrating n-type and/or p-type reactivity. For the past 50 years, several kinds of organic redox active moieties have been identified, such as quinones, diimides or some stable radicals. Our group strives notably for developing air-stable lithiated materials in order to reach high output voltage as recently demonstrated with magnesium (2,5-dilithium-oxy)-terephthalate. It allows reversible delithiation/lithiation electrochemical reaction at an average potential of 3.4 V vs Li /Li coupled with 92% capacity retention over 80 cycles at 20°C, and a specific capacity reaching ~100 mAh/g. Within this background, this contribution aims at reporting the design, the synthesis as well as the electrochemical behavior of other lithiated compounds based on the terephthalate backbone.

Authors : Gabriela Queirós(1,2), Joana S. Teixeira(1,3), André M. Pereira(3), Clara Pereira(1), Natalia Rey-Raap(4), Manuel Fernando R. Pereira(2)
Affiliations : (1) REQUIMTE/LAQV, Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal. (2) Associate Laboratory LSRE-LCM, Department of Chemical Engineering, Faculty of Engineering, University of Porto, R. Dr. Roberto Frias s/n, 4200-465 Porto, Portugal. (3) IFIMUP ? Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Department of Physics and Astronomy, Faculty of Sciences, University of Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal. (4) Department of Physical and Analytical Chemistry, Oviedo University-CINN, 33006, Oviedo, Spain

Resume : Nowadays, the demand for renewable energy sources has grown significantly to reduce the greenhouse effect into the atmosphere. There is also a need for more efficient energy storage devices to positively contribute to the environment. Therefore, in recent decades, supercapacitors have received a lot of attention as a green energy storage solution. Supercapacitors are an electrochemical energy storage technology that presents higher power density than batteries, which allows them to charge faster. Moreover, they offer excellent cycling stability and significantly longer life cycle. Textile-based wearable devices allow the supply of energy to vital sign monitoring sensors, lighting systems, among other flexible/portable electronic devices, with high charging speed, safety, lightness, flexibility and durability. In order to satisfy the needs of society concerning electrochemical energy storage devices for wearables, all-solid-state flexible supercapacitors are being developed. Carbon-based materials have received increasing attention as supercapacitor electrode materials because of their high specific surface area, good electrical conductivity and excellent stability. In recent years, the use of biomass-derived activated carbons as electrode materials has grown for supercapacitor applications because they are prepared from low-cost sustainable resources. Thus, in this work, glucose-derived carbon/multi-walled carbon nanotube (MWCNT) hybrid materials were prepared by hydrothermal carbonization of glucose in the presence of different amounts of MWCNTs and subsequent physical activation. The new hybrids were then used as electrode active materials for the fabrication of supercapacitor textile electrodes and devices by a dip-pad-dry process using cotton fabric as substrate. The all-solid-state flexible supercapacitors were designed in sandwich-type configuration with a solid-gel electrolyte. The prepared hybrid materials have a high specific surface area and a large volume of micropores due to the physical activation with CO2. The influence of the presence and amount of CNTs in the hybrids on the electrochemical performance of the as-prepared devices was evaluated and discussed through cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy measurements. The devices? energy storage performance is also compared with that of supercapacitors based on commercial activated carbons, considering the obtained values from capacitance, power density and energy density. Acknowledgements: This work was financially supported by FEDER through COMPETE 2020-POCI and by FCT/MCTES under Program PT2020 (PTDC/CTM-TEX/31271/2017, UIDB/50006/2020, UIDB/04968/2020), UIDB/50020/2020 of the Associate Laboratory LSRE-LCM - funded by national funds through FCT/MCTES (PIDDAC). GQ, JST and CP thank FCT for MSc. grant (PTDC/CTM-TEX/31271/2017), PhD scholarship (SFRH/BD/145513/2019) and FCT Investigator contract (IF/01080/2015), respectively.

Authors : Ilaria Fratelli (1)(2), Laura Basiricò (1)(2), Andrea Ciavatti (1)(2), John Anthony (3), Ioannis Kymissis (4), Beatrice Fraboni (1)(2)
Affiliations : 1) Department of Physics and Astronomy, University of Bologna, Bologna, Italy 2) National Institute of Nuclear Physics (INFN), Section of Bologna, Bologna, Italy 3) University of Kentucky, Center for Applied Energy Research, United States 4) Department of Electrical Engineering, Columbia University, New York, New York 10027, United States

Resume : High energy radiation direct detectors based on organic semiconductors allow to overcome several limits imposed by the common inorganic technologies. In fact, this class of materials can be deposited by solution, allowing low-cost and low-temperature fabrication processes and making possible to obtain flexible and large-area devices directly printed onto plastic substrates. Such peculiar property makes this class of materials very appealing for high energy radiation detection, especially for applications where the portability, flexibility and large-area dimension are becoming essential task. Furthermore, organic materials are human tissue-equivalent in terms of radiation absorption and for this reason they form a potential platform for the development of dosimeters to be employed for the monitoring of the radiation absorbed by a patient during both medical diagnostic exams or during radiotherapy [1], [2]. Here we report two main properties offered by organic semiconductors employed to develop and study X-ray detectors based on arrays of Organic Field Effect Transistors. First, we took advantage of the ease of chemically tailor the organic materials and we employed a new synthetized organic small molecule (i.e. TIPGe-Pn) derived from TIPS-Pn (bis-(triisopropylsilylethynyl)-pentacene) by substituting the two silicon atoms with two germanium atoms. In fact, thanks to the higher atomic number, we increased the cross section of interaction between the high energy photons and the organic active layer leading to the enhancement of the radiation detection capability [3]. Second, exploiting the possibility of depositing the organic semiconductors from solution, we employed a novel technique called Pneumatic Nozzle Printing [4] which allowed us to deposit organic thin films in a fully controlled way. Thus, by varying the deposition parameters (e.g. temperature, deposition speed) it has been possible to tune the dimensions and the alignment of the microcrystalline structures forming the organic thin film. As it has been already demonstrated [5] this represents an important tool to set both the transport and detecting properties of the devices. Both these two strategies based on peculiar and unique characteristics of organic semiconductors allowed us to reach outstanding performances in terms of high energy radiation detection leading the possibility to assess the operation of this class of sensors in actual clinical environments [6]. References [1] A. M. Zeidell et al., Adv. Sci., p. 2001522, Jul. 2020. [2] H. M. Thirimanne et al., IEEE Trans. Nucl. Sci., vol. 9499, no. c, pp. 1?1, 2020. [3] A. Ciavatti et al., Adv. Funct. Mater., p. 1806119, Dec. 2018. [4] S. Yang et al., Adv. Electron. Mater., vol. 4, no. 6, pp. 4?9, 2018. [5] I. Temiño et al., Nat. Commun., vol. 11, no. 1, pp. 1?10, 2020. [6] L. Basiricò et al., Front. Phys., vol. 8, no. February, pp. 1?11, 2020.

Authors : Lamiaa Fijahi, Tommaso Salzillo, Adrián Tamayo, Yves Geerts, Marta Mas-Torrent*
Affiliations : Department of Molecular Nanoscience and Organic Materials, Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193, Bellaterra, Spain

Resume : Charge transfer (CT) complexes have attracted great attention because of their potential as a new type of organic semiconductor material. Organic charge-transfer salts are formed from electron acceptors (e.g. tetracyanoquinodimethane, TCNQ) and electron donors (e.g. tetrathiafulvalene, TTF), and provide a new material with new physical properties. However, their application in organic field-effect transistors has mainly been limited to ideal single crystals or to films prepared by the co-evaporated of their components. Herein, we prepared OFETs of the CT salt based on C8-O-BTBT-OC8 /F4TCNQ by a simple solution shearing technique (BAMS). This was carried out by blending the active materials with polystyrene to promote film processability, reproducibility, and stability. X-ray and Raman spectroscopy were used for charge transfer degree estimation and structural identification of the films. The resulting OFET devices, fabricated and measured in inert atmosphere and environmental conditions, exhibited an n-type behavior. Keywords: OFET, charge Transfer, solution shearing technique, n-type.

Authors : Mariana Rocha, Margarida Maia, André Pereira
Affiliations : Mariana Rocha; Margarida Maia; André Pereira - IFIMUP ? Instituto de Física de Materiais Avançados, Nanotecnologia e Fotónica, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal

Resume : During the past few decades, with rapid enlargement of human society, consumption of traditional energy has increased exponentially. Thermoelectric materials (TE) can generate electrical energy when they are exposed to a thermal gradient, considered one of the most important solutions for sustainable energy harvesting.1,2 These materials present lightweight, small size, pollution free and recycling potential.2 One of the most used TEs is the alloy Bi2Te3 since it is considered as the best performing thermoelectrical material near room temperature (150-300 K).2 The performance of a thermoelectric material is assessed by a dimensionless figure-of-merit, zT, defined as zT = S2?T/(?e + ?l), where S, ?, ?e, ?l and T are the Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, and the absolute temperature, respectively. An average zT between 1.5?2 can enable substantial waste-heat harvesting and application in primary power generation.3 Recently, in order to obtain high zT values, was developed Bi2Te3 nanomaterials leading thus a strong quantum confinement and a significant reduction of the lattice thermal conductivity, causing an increase of the zT value.4 Herein, it was prepared Bi2Te3 NPs using a chemical reduction process and a polyol to confine the NPs size.5 The NPs were characterized by XRD, DLS, SEM and transport properties presenting a mix of Bi2Te3 with a small amount of Te, an average hydrodynamic diameter of 261±23 nm (PDI = 0.31±0.04, n = 5), S = +172.8 µV K-1 (being p-type material), ? = 22.20 S mm-1, and a Power Factor of 0.662 µW m-1 K-2. Acknowledgements: This work was funded by H2020-EU.1.2.1. - FET Open Project (WiPTherm, grant agreement ID: 863307). References: 1. P. Srivastava and K. Singh, Bull. Mater. Sci., 2013, 36, 765?770. 2. M. M. Rashad, A. El-Dissouky, H. M. Soliman, A. M. Elseman, H. M. Refaat and A. Ebrahim, Mater. Res. Innov., 2017, 22, 1?9. 3. T. Nakamoto, S. Yokoyama, T. Takamatsu, K. Harata, K. Motomiya, H. Takahashi, Y. Miyazaki and K. Tohji, J. Electron. Mater., 2019, 48, 2700?2711. 4. Y. Xu, Z. Ren, W. Ren, G. Cao, K. Deng and Y. Zhong, Mater. Lett., 2008, 62, 4273?4276. 5. K. Kim, H. M. Lee, D. W. Kim, K. J. Kim, G. G. Lee and G. H. Ha, J. Korean Phys. Soc., 2010, 57, 1037?1040.

Authors : S. Maryam Sadeghi1, Rui S. Costa1|2, Joana S. Teixeira1|2, Clara Pereira2, Andre M. Pereira1
Affiliations : 1IFIMUP, Institute of Physics for Advanced Materials, Nanotechnology and Photonics, Physics and Astronomy Department, Faculty of Sciences, University of Porto, Porto, Portugal 2REQUIMTE/LAQV, Chemistry and Biochemistry Department, Faculty of Sciences, University of Porto, Porto, Portugal

Resume : Recently, the demand for intelligent textile and smart material is growing enormously in the world in every field of engineering, and technology. Smart textiles are one of the areas that can provide incalculably beneficial solutions and high value products for a variety of applications, such as health monitoring, sports, military, etc. [1]. Electrochemical energy storage systems like supercapacitors (SCs) are promising technologies to develop smart functionalities on textiles. Carbon-based materials have been incorporated in fabrics to fabricate textile supercapacitors (TSCs) owing to their unique features that make them highly applicable as a SC material. The most highlighted features of these material are their high electrical conductivity, increased surface area, desirable mechanical properties, high chemical and thermal stability [2]. However, the scalable fabrication of TSCs is still on an infancy stage and needs to be improved. Screen-printing is a widely used technique in industry due to its simplicity, substrates and inks versatility, exhibiting great potential for scaling up [1]. Hence, in this work, screen-printing method was used to produce SCs onto different substrates: polyethylene terephthalate (PET) and cotton textile. To fabricate the electrodes, two commercial conductive carbon-based inks were used. The SC electrodes were prepared with the configuration of 2D planar interdigital pattern in different sizes and the ink was passed through a flat patterned screen onto a PET and textile 1 and 2 times, respectively. The electrodes were then coated with a solid-gel electrolyte (PVA/H3PO4). The electrochemical performance of the SCs was evaluated by cyclic voltammetry, galvanostatic charge/discharge tests and in an impedance setup. The results unveiled the EDLC-type nature of the SCs. The best electrochemical performance was observed in PET devices which is a consequence of smooth and impenetrable surface of PET compare with TSCs. In conclusion, this work constitutes a step forward to a better understanding of the performance of fully screen-printed SCs as a simple and scalable process, which can be tuned by increasing the layers of ink and PVA/H3PO4 coating, and by changing the geometrical specifications of the electrode. Acknowledgements: Work funded by FEDER through COMPETE 2020 (POCI) and by Fundação para a Ciência e a Tecnologia (FCT)/MCTES through Program PT2020 (project PTDC/CTM-TEX/31271/ 2017) and through national funds (UIDB/50006/2020 and UIDB/04968/2020). R.S.C. thanks for the grant funding from the European Union?s Horizon 2020 Research and Innovation Program under Grant Agreement No. 863307. C.P. thanks FCT for the FCT Investigator contract IF/ 01080/2015. S.M.S thanks the project PTDC/CTM-TEX/31271/ 2017 for this junior research contract. References: 1. Pereira, C. et al. (2020). Handbook of Functionalized Nanomaterials for Industrial Applications, 611-714 2. Costa, R.S. et al. (2020). J Mater Sci., 10121-10141

Authors : Zhu Meng, Ernest Pastor, Shababa Selim, Andreas Kafizas, James Durrant and Artem Bakulin
Affiliations : a Department of Chemistry, Molecular Science Research Hub, Imperial College London, London W12 0BZ, United Kingdom b Institut de Ciències Fotòniques (ICFO), The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain

Resume : In solar water splitting devices, revealing the contribution of defect states on photoconversion is of paramount importance for designing efficient photoelectrodes. To observe the dynamics of trap carriers, we designed a pump-push-photocurrent (PPPC) setup in nanosecond-to-microsecond time domain. The designed PPPC setup can optically manipulate carriers and detect their in-situ dynamics. A near-IR (1064 nm) light is used to re-active the electrons in trap states. Using the ns PPPC setup, we studied a monoclinic bismuth vanadate (BiVO4) as a model system. This metal oxide is a promising photoanode for water splitting but the ambiguous effect of oxygen vacancy states restricts the development of device performance. Here, we show that defect state is acting as electron trap and hole trap during solar water splitting. Moreover, the function of state is strongly affected by the applied bias on photoelectrochemical (PEC) cell. Under low bias, defect state work as recombination centre and consumes photogenerated carriers. However, as bias increasing, OV state work as electron trap, improved donor density and extended carrier lifetime. These studies are an important step towards the understanding of oxygen vacancies and their effect on the performance of BiVO4 photoanodes for water splitting, and could be used to guide the design of more efficient photocatalysts.

Authors : Massimiliano Comin, Simone Fratini, Xavier Blase, Gabriele D?Avino.
Affiliations : Institut Néel, CNRS, and Univ. Grenoble Alpes, 38000 Grenoble, France

Resume : The success of electronic and optoelectronic technologies relies on the possibility to tweak the energies of transport levels by molecular doping. In this context, Coulomb interactions between host molecules and ionized dopants play a key role in the energetics of doped organic semiconductors as they control dopant ionization, but also lead to strongly bound charge carriers. [1,2] By taking the paradigmatic case of F4TCNQ-doped pentacene, we show with first-principles calculations that the charge-transfer polarizability associated with host-dopant complexes can be up to one order of magnitude higher than that of the host semiconductor. The consequence of this dopant-induced increased polarizability is a dramatic enhancement of the macroscopic dielectric response of the doped material, ultimately helping the release of free carriers. Classical Micro-Electrostatics calculations reveal that the bulk dielectric response of the doped semiconductor tends towards a divergence at doping concentrations of 5-7%, similar to those determining conductivity enhancements of a few orders of magnitude in typical experiments. Our results suggest that such a doping-induced dielectric catastrophe may represent a driving factor for the insulator-to-metal transition in doped organic semiconductors. [3] References 1. Gaul et al., Nature Materials 17, 439 (2018) ; Schwarze et al., Nature Materials 18, 242 (2019) 2. Li, D?Avino, Pershin, Jacquemin, Duchemin, Beljonne Blase, Phys. Rev. Mater. 1, 025602 (2017) 3. Comin, Fratini, Blase, D?Avino, in preparation.

Authors : Nora Gildemeister(1), Fabrizia Negri(2), Klaus Meerholz(1), and Daniele Fazzi(1)
Affiliations : (1) Insitut für Physikalische Chemie, Department Chemie, Universität zu Köln, Gre- instr. 4-6, D - 50939 Köln (2) Dipartimento di Chimica, Università di Bologna, via F. Selmi 2, 40126 Bologna, Italy

Resume : Dipolar merocyanines, a versatile class of organic pi-conjugated molecules, are investigated for their self-assembly and opto-electronic properties. The accurate description of their molecular, electronic and vibrational structure remains a challenge due to strong electron correlation effects and long-range inter-molecular interactions. [1-2] We found constrained DFT and DFT/PCM calculations to be effective embedding methods to correctly asses the molecular and electronic structure in single crystals. Via a bottom-up approach we report a comprehensive analysis modelling intra- and inter-molecular charge transport properties, such as reorganization energies, transfer integrals and final charge mobilities, for a library of different donor-acceptor units and lateral groups. Further, we suggest a supramolecular approach to account for the internal and external contribution to the reorganization energy. Charge mobilities were computed within the semiclassical nonadiabatic electron-transfer theory by analyzing different single crystals and highlighting the impact of side groups and casting conditions. Computed and experimental values are in good agreement. Our modelling suggests that charge diffusion maximizes when dipolar molecules are packed in slipped anti-symmetric pairs, arranged in 2D interconnected architectures. [3] [1] C. Brückner, et al., J. Phys. Chem. C 2015, 17602-17611. [2] D. Bialas, et al., J. Phys. Chem. C 2019, 123, 30, 18654-18664. [3] N. Gildemeister, et al., 2021, Paper in preperation

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Chargetransport / Thermoelectric effect : Simone Fabiano
Authors : Dorothea Scheunemann(1), Tanvi Upreti (1), Martijn Kemerink(1,2)
Affiliations : 1) Complex Materials and Devices, Linköping University, Sweden 2) Centre for Advanced Materials, University of Heidelberg, Germany

Resume : Despite significant progress in terms of the practical performance of organic thermoelectrics (OTE), it is unclear what the ultimate values for performance indicators of OTE could reasonably be. In this talk I will give an overview of our recent work to develop and calibrate both semi-analytical and numerical models for the observables that make up the power factor PF and the figure of merit zT, that is the electrical and thermal conductivity as well as the Seebeck coefficient, of OTE. The investigated models are based on the Gaussian disorder model and are shown to provide excellent agreement with experiments provided hopping beyond the nearest neighbor is accounted for and it will be shown that the recent Kang-Snyder model is a phenomenological representation of a hopping model. An extension to describe the electronic part of the thermal conductivity will be presented and it will be shown that for most practical systems presented so far, the thermal conductivity is dominated by the lattice component. Only at very high electrical conductivities, requiring both high doping levels and high mobility, does the electrical component become important. Counterintuitively, under these conditions, reaching beyond zT=1 will require suppressing the lattice thermal conductivity to below 0.2 W/mK. Finally, it will be shown that under the right conditions, aligning by stretching or drawing is a universal method to break the paradigm that thermopower and conductivity cannot be simultaneously increased.

Authors : Jian Liu[1], Gang Ye[1,2], Hinderikus G.O. Potgieser[1], Marten Koopmans[1], Selim Sami[1,2], Mohamad Insan Nugraha[3], Diego Rosas Villalva[3], Hengda Sun[4], Jingjin Dong[1], Xuwen Yang[1], Xinkai Qiu[1,2], Chen Yao[2], Giuseppe Portale[1], Simone Fabiano[4], Thomas D. Anthopoulos[3], Derya Baran[3], Remco W. A. Havenith[1,2,4], Ryan C. Chiechi[1,2], and L. Jan-Anton Koster[1]
Affiliations : [1] Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen NL-9747 AG, The Netherlands [2] Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, Groningen NL-9747 AG, The Netherlands [3] King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Division (PSE), KAUST Solar Center (KSC), Thuwal 23955-6900, Saudi Arabia [4] Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, SE-601 74 Norrköping, Sweden [5] Department of Inorganic and Physical Chemistry, Ghent University, Krijgslaan 281-(S3), B-9000 Ghent, Belgium

Resume : There is no molecular strategy for selectively increasing the Seebeck coefficient without reducing the electrical conductivity for organic thermoelectrics. Here, it is reported that the use of amphipathic side chains in an n-type donor-acceptor copolymer can enable one to selectively increase the Seebeck coefficient and thus increase the power factor by a factor of ~ 5. The amphipathic side chain contains an alkyl chain segment that acts as a spacer between the polymer backbone and an ethylene glycol type chain segment. The use of this alkyl spacer can not only reduce the energetic disorder in the conjugated polymer film but can also properly control the dopant sites away from the backbone, which minimizes the adverse influence of counterions. As confirmed by kinetic Monte Carlo simulations with the host-dopant distance as the only variable, a reduced Coulombic interaction resulting from a larger host-dopant distance contributes to a higher Seebeck coefficient for a given electrical conductivity. Finally, an optimized power factor of 18 ?W/mK2 is achieved in the doped polymer film. This work provides a facile molecular strategy for selectively improving the Seebeck coefficient and opens up a new route for optimizing the dopant location towards realizing better n-type polymeric thermoelectrics.

Authors : C. Vael, S. Jenatsch, S. Züfle, F. Nüesch, B. Ruhstaller
Affiliations : Vael, Jenatsch, Züfle, Ruhstaller - Fluxim AG, Katharina-Sulzer-Platz 2, 8400 Winterthur, Switzerland; Nüesch - Dübendorf Empa Ueberlandstrasse 129, 8600 Dübendorf, Switzerland

Resume : Trapping of charge carriers in organic electronic devices like organic light-emitting diodes (OLEDs), organic field effect transistors (OFETs) and organic solar cells has a detrimental effect on charge mobility, device lifetime and device efficiency. It is therefore essential to have reliable techniques for probing localized states and their energy distribution in order to understand and minimize the formation of trap states. There are only few methods which directly measure the electrical properties of traps. One of these techniques is thermally stimulated current (TSC) which can detect traps with very low concentrations. However, it is not straightforward to extract important trap parameters such as the capture rate coefficient and activation energy from TSC curves. The reason is that assumptions about relative rates of detrapping, retrapping and recombination of charge carriers inside the material that have to be made in order to find an analytical expression which allows for trap parameter determination. Here we use drift-diffusion simulations to generate synthetic TSC data of an organic solar cell with homogeneously distributed trap states. This data is used to test the validity of various analytical and empirical formulas, with different levels of complexity, that are typically employed to extract trap parameters, namely trap depth, density and capture rate. We found that for a range of the capture rate coefficient from 10-11 to 10-10 cm3/s, neither the assumption of fast retrapping nor fast recombination is yielding correct trap parameter values. Also, for samples with a thickness larger than 200 nm, analytical formulas may give values that deviated from the simulated input value. This is due to multiple retrapping effects that occur and thus distort the peak shape. Furthermore, we present the simulated trap occupation profile of the semiconductor layer during the TSC ramp. We can show that especially deep traps are not entirely emptied upon heating which is a major reason for the underestimation of the total trap density.

11:00 DISCUSSION    
Charge transport, structure-function III : Sophia Hayes
Authors : Gonzague Rebetez, Olivier Bardagot, Julien Réhault, Natalie Banerji
Affiliations : Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern

Resume : Organic Electrochemical Transistors (OECTs) are sensitive sensors used for example in biological applications. They can be described using two circuits: an ionic circuit and an electronic circuit. The former arises from ions penetrating an organic channel due to switching of the gate and causing an electrochemical (de)doping reaction, while the latter arises form source-drain electron flow across the organic channel. In the last years, advancing our knowledge of OECTs has allowed a drastic increase of their performance, however a complete picture of the two circuits and how they interact is still lacking. Here, we will introduce two spectroscopic techniques to study the ionic and electronic transport processes in OECTs: 1) Voltage-gated UV-vis absorbance unravels the kinetics of the ionic circuit and (de-)doping process. This measurement monitors the electrochemical reactions in the organic channel with millisecond temporal resolution and allows to determine the thermodynamics using the temperature-dependence of the dynamics. 2) In-situ THz absorption measurements investigate the electronic circuit. This probes the nature of the electronic charges and the nanoscale conductivity of the organic channel. Results on PEDOT:PSS based OECTs will be presented. A deep understanding of the internal mechanisms occurring in OECTs is an essential step towards further interfacing with elaborate biological systems.

Authors : Julie Euvrard, Oki Gunawan, Xinjue Zhong, Steven P. Harvey, Antoine Kahn, David B. Mitzi
Affiliations : Julie Euvrard: Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA. ; Oki Gunawan: IBM T. J. Watson Research Center, Yorktown Heights, NY, USA. ; Xinjue Zhong: Department of Electrical Engineering, Princeton University, Princeton, NJ, 08544, USA. ; Steven P. Harvey: National Renewable Energy Laboratory, Golden, CO 80401, USA. ; Antoine Kahn: Department of Electrical Engineering, Princeton University, Princeton, NJ, 08544, USA. ; David B. Mitzi: Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA and Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.

Resume : Electronic technologies critically rely on the ability to broadly dope the active semiconductor; yet the promising class of halide perovskite semiconductors so far does not allow for significant control over carrier type (p- or n-) and density. Taking advantage of the experience acquired from doping inorganic and organic semiconductors, various doping strategies have been explored in halide perovskites. Molecular doping appears among the most promising techniques for perovskites, with early works suggesting efficient tuning of the carrier properties at the film surface through charge transfer with a sequentially-deposited molecular layer. Yet, more homogeneously integrated molecular dopants in perovskite films have only just begun to be explored and have so far yielded modest conductivity enhancement. Here, we demonstrate efficient 3D p-doping in a halide perovskite using the molecular dopants 2,3,5,6-tetrafluorotetracyanoquinodimethane (F4TCNQ) directly interspersed in the perovskite precursor solution. With an ionization energy (IE) of ~5.4 eV, the widely studied MAPbI3 perovskite is not expected to allow efficient charge transfer with the F4TCNQ lowest unoccupied molecular orbital, given the molecule?s electron affinity (EA) of 5.24 eV. To achieve an appropriate energy level alignment, Pb is blended with Sn to form MAPb1-xSnxI3, leading to a decrease in IE with increasing Sn content. Employing x=0.5, we show for the first time a tuning range of up to 5 orders of magnitude for halide perovskite conductivity using a molecular dopant. AC Hall effect measurements provide evidence of the doping effect, with measured free hole carrier density from ~10^13 cm-3 to ~10^17 cm-3. P-doping is further confirmed through measurements of Fermi level shift toward the perovskite valence band maximum, along with an increase in work-function, as observed using ultraviolet photoemission spectroscopy and Kelvin probe-based contact potential difference measurements. The dopant molecules are shown to localize at the perovskite grain boundaries and throughout the film thickness using tomography (3D) time-of-flight secondary-ion mass spectroscopy. Fourier transform infrared spectroscopy measurements support F4TCNQ ionization and confirm the reduced charge transfer efficiency with increased Pb content (increase in the perovskite IE), highlighting the need for appropriate perovskite-dopant energy level alignment for effective doping. Finally, a deep trap passivation effect of doping is revealed with carrier-resolved photo-Hall (CRPH) measurements, as a hole (majority carrier) lifetime increase by more than one order of magnitude is observed with doping. The study highlights the potential of molecular doping to effectively tune carrier density and optoelectronic properties in perovskites, and opens the door to future in-depth studies towards optimized perovskite doping.

Authors : Nathaniel P. Gallop, Dmitry R. Maslennikov, Katelyn P. Goetz, Yana Vaynzof, Artem A. Bakulin
Affiliations : Dept. of Chemistry, Imperial College London, 83 Wood Lane, London, W12 0BZ, United Kingdom; Technische Universität Dresden, Dresden, Germany 01062

Resume : Since their first use as photovoltaic absorbers in 2009, organohalide perovskites (OHPs) have proven to be among the most promising of the so-called 3rd generation photovoltaic technologies, owing to their superlative photovoltaic efficiencies (having achieved a power conversion efficiency of ~25% in 2020), broad tuneabilities, and low production costs. For this reason, they have attracted considerable research attention, with close to 2000 publications in 2018 alone. In spite of this herculean effort by the research community, there are still many things we do not know about perovskite photovoltaics. Their soft nature and dynamic disorder, which arise from the interplay between the organic and inorganic sublattice that together comprise the material, make developing a comprehensive understanding of their microscale dynamical behaviour very difficult. In particular, the degree to which the dynamics of the organic and inorganic sub-lattices are coupled to one and other has generated considerable controversy within the literature, with researchers coming to conflicting conclusions about the nature and extent of the coupling. This is exacerbated in no small part by the relative dearth of conventional experimental techniques able to achieve the high sensitivities, selectivities, and time resolution needed to resolve this effect. In this talk, I will discuss our development of a novel spectroscopic technique, which we term Photocurrent Detected Vibrationally Promoted Electronic Resonance (PC/VIPER). This technique combines the so-called VIPER pulse sequence?first conceived as an extension to 2D-EXSY experiments?with a highly sensitive interferometric photocurrent detection scheme, enabling us to both spectrally and temporally resolve the effect of vibrational transitions of the electronic properties of the organohalide perovskite FAPbBr3. We find that stimulation of the C=N stretching mode of formamidinium weakly modulates the bandgap of FAPbBr3, with this effect being entirely absent in all-inorganic CsPbBr3. Through comparison with Ab Initio molecular dynamics and time-resolved IR of other perovskite systems, we rationalize this modulation as resulting from a weak coupling between the organic and inorganic sub lattices, which distorts the inorganic lattice sufficiently to alter the bandgap. We conclude that, whilst the overall effect is weak, A-site cation dynamics cannot be entirely discounted when considering the optoelectronic behaviour of certain organohalide perovskites.

12:15 DISCUSSION    
Modelling doping effects in organic materials : Daniele Fazzi
Authors : Jing Li, Gabriele D'Avino, Ivan Duchemin, David Beljonne, Xavier Blase
Affiliations : Institut Néel, CNRS and UGA, F-38042 Grenoble, France; Institut Néel, CNRS and UGA, F-38042 Grenoble, France; CEA, IRIG-MEM-LSim, 38054 Grenoble, France; Laboratory for Chemistry of Novel Materials, University of Mons, BE-7000 Mons, Belgium; Institut Néel, CNRS and UGA, F-38042 Grenoble, France

Resume : We study the electronic properties of dopants in organic systems on the basis of state-of-the-art many-body GW and Bethe-Salpeter formalisms accounting for proper electrostatic and dielectric environments. [1,2] We show in particular that the absolute energy position of doping levels and band edges of organic semiconductors can be obtained with accuracy both in the bulk and at the surface. Our calculations reveal in particular that the energy levels of a molecular impurity strongly depend on the host environment as a result of electrostatic intermolecular interactions. [3] Concerning doping mechanisms, we demonstrate that ionisation of the dopants can occur even in situations of very deep acceptor (donor) levels thanks to strong electron-hole interactions stabilising charge-transfer states. [4] The increase of conductivity requires from then on to understand the charge separation of these bound electron-hole pairs in order to generate free carriers. [1] J. Li, G. D'Avino, I. Duchemin, D. Beljonne, X. Blase, J. Phys. Chem. Lett. 2016, 7, 2814. [2] J. Li, G. D'Avino, I. Duchemin, D. Beljonne, X. Blase, Phys. Rev. B 2018, 97, 035108. [3] Jing Li, Ivan Duchemin, Otello Maria Roscioni, Pascal Friederich et al., Materials Horizons 2019, 6, 107-114. [4] J. Li, G. D'Avino, A. Pershin, D. Jacquemin, I. Duchemin, D. Beljonne, X. Blase, Phys. Rev. Materials 2017, 1, 025602.

Authors : Pablo Simón Marqués?, Giacomo Londi?, Brett Yurash?, Thuc-Quyen Nguyen?, Stephen Barlow§, Seth R. Marder§ and David Beljonne?
Affiliations : ?Laboratoire MOLTECH-Anjou, UMR CNRS 6200, UNIV Angers, SFR MATRIX, 2 Bd Lavoisier, 49045 Angers Cedex, France ?Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, 7000 Mons, Belgium ?Center for Polymers and Organic Solids, Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106, United States of America §Center for Organic Photonics and Electronics, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, 30332?0400, United States of America

Resume : We report on computational studies of the potential of three borane Lewis acids (LAs) (B(C6F5)3 (BCF), BF3, and BBr3) to form stable adducts and/or to generate positive polarons with three different semiconducting ?-conjugated polymers (PFPT, PCPDTPT and PCPDTBT). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations based on range-separated hybrid (RSH) functionals provide insight into changes in the electronic structure and optical properties upon adduct formation between LAs and the two polymers containing pyridine moieties, PFPT and PCPDTPT, unravelling the complex interplay between partial hybridization, charge transfer and changes in the polymer backbone conformation. We then assess the potential of BCF to induce p-doping in PCPDTBT, which does not contain pyridine groups, by computing the energetics of various reaction mechanisms proposed in the literature. We find that reaction of BCF(OH2) to form protonated PCPDTBT and [BCF(OH)]-, followed by electron transfer from a pristine to a protonated PCPDTBT chain is highly endergonic, and thus unlikely at low doping concentration. The theoretical and experimental data can, however, be reconciled if one considers the formation of [BCF(OH)BCF]- or [BCF(OH)(OH2)BCF]- counterions rather than [BCF(OH)]- and invokes subsequent reactions resulting in the elimination of H2.

Authors : Marten Koopmans, Miina A. T. Leiviskä, Jian Liu, Jingjin Dong, Li Qiu, Jan C. Hummelen, Giuseppe Portale, Michael C. Heiber, L. Jan Anton Koster
Affiliations : Marten Koopmans ? Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands; Miina A. T. Leiviska? ? Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands; Jian Liu ? Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands; Jingjin Dong ? Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands; Li Qiu ? Zernike Institute for Advanced Materials and Stratingh Institute for Chemistry, University of Groningen, Groningen 9747 AG, The Netherlands; Jan C. Hummelen ? Zernike Institute for Advanced Materials and Stratingh Institute for Chemistry, University of Groningen, Groningen 9747 AG, The Netherlands; Giuseppe Portale ? Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands; Michael C. Heiber ? Center for Hierarchical Materials Design, Northwestern University, Evanston, Illinois 60208, United States; L. Jan Anton Koster ? Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747 AG, The Netherlands;

Resume : In order to make rational improvements of the charge transport properties of organic semiconductors, a thorough understanding of this rather complex process is needed. Charge carrier transport in organic semiconductors is usually described as a series of events where a charge carrier hops from one localised state to the next. In this type of description, the disordered nature of such systems leads to a broad distribution of site energies. As a result, the mobility of charge carriers increases as more charge carriers are introduced unless the number of charges is relatively low. While it has been recognised that Coulomb interactions between dopants and charge carriers are important, carrier-carrier interactions?interactions among charge carriers?in doped organics have received less attention. In a doped organic semiconductor, however, the number of (free and bound) charge carriers equals the number of reacted dopants. As a result, both types of interactions are of importance for a proper description of the transport properties of doped organic semiconductors. However, it has been proposed that carrier-carrier interactions is significantly weaker than the effect of Coulomb interactions between dopants and charge carriers. In this contribution, we use a kinetic Monte-Carlo model to study the transport properties in the presence of dopants and including both carrier-carrier and carrier-dopant interactions. In particular, we can simulate up to the relatively high doping densities that are experimentally relevant even though numerically challenging. We find that the density of states (DOS) of such systems shows a pseudo-gap at the Fermi level due to Coulomb interactions between the charge carriers [1]. Such Coulomb gaps are a manifestation of the carrier-carrier interactions and have been predicted to exist in hopping systems, but are usually washed out at anything other than very low temperatures. This has profound implications for electrical conductivity as the pseudo-gap limits charge carrier transport at high doping densities. Experimentally, we observe that the electrical conductivity of a large number of organic semiconductors shows a maximum: Upon increased doping levels the conductivity decreases. This type of behaviour is commonly attributed to changes in the microstructure as a consequence of doping. However, we find that even when using vapour doping, where there are no observable changes in the microstructure, this behaviour persists.  The experimental findings match the Monte-Carlo data very closely, which implies that the Coulomb pseudo-gap is at the root of the limited conductivity at high doping densities. [1] Marten Koopmans, Miina A. T. Leiviskä, Jian Liu, Jingjin Dong, Li Qiu, Jan C. Hummelen, Giuseppe Portale, Michael C. Heiber, and L. Jan Anton Koster ACS Applied Materials & Interfaces 50, 56222-56230 (2020).

15:00 DISCUSSION    
Charge transport, structure-function IV : Christian NIELSEN
Authors : John Grey David Walwark Jian Gao
Affiliations : Department of Chemistry, University of New Mexico

Resume : Charge transfer doping of organic semiconductors provides additional avenues for tuning electrical properties and charge transport characteristics in devices. Unintentional doping of organic materials by contaminants may also occur leading to alterations in functionality and performance. We examine doping in conjugated organic polymers with emphasis on polymer conformational and packing order influence interactions with intentional and unintentional dopants before and after contact. Self-assembled polymer aggregate nanostructures are used as platforms for understanding how structure affects doping interactions and efficacies. We demonstrate the importance of packing and conformational order and accompanying structural displacements on doping outcomes that should be considered alongside electronic factors.

Authors : Li Jinghai, Raphael Ptattner, Marta Mas-Torrent
Affiliations : Institut de Ciència de Materials de Barcelona (ICMAB-CSIC) and CIBER-BBN, Campus de la UAB, Bellaterra, 08193, Spain

Resume : Organic semiconductor films fabricated from solution processes have great potential for spurring the development of electronic devices. However, the performance of such devices is affected by external factors such as water or oxygen. [1-2] Here, thin films of the organic semiconductor diF-TES-ADT blended with polystyrene (PS)were prepared by bar-assisted meniscus shearing (BAMs) technique using a home-designed equipment (Figure 1).[3] All the fabrication process was carried out under ambient conditions. This film has shown excellent electrical properties with a high hole mobility around 1 cm2/Vs.[4] The OFET devices based on diF-TES-ADT: PS blend films were measured under different conditions: ambient, in a glovebox, under Nitrogen, under Argon and in high vacuum. These measurements combined with temperature dependence measurements and quartz crystal microbalance and capacitance characterizations permitted to perform a deep analysis of how water influences the performance of OFETs devices. Besides, the dopant F4TCNQ was introduced into the film to minimize the effect of water and to control the device properties. [1] Nikolka, Mark, et al. "Performance Improvements in Conjugated Polymer Devices by Removal of Water?Induced Traps." Advanced materials 30.36 (2018): 1801874. [2] Zuo, Guangzheng, et al. "General rule for the energy of water-induced traps in organic semiconductors." Nature materials 18.6 (2019): 588-593. [3] del Pozo, Freddy G., et al. "Single Crystal?Like Performance in Solution?Coated Thin?Film Organic Field?Effect Transistors." Advanced Functional Materials 26.14 (2016): 2379-2386. [4] Temiño, Inés, et al. "A Rapid, Low?Cost, and Scalable Technique for Printing State?of?the?Art Organic Field?Effect Transistors." Advanced Materials Technologies 1.5 (2016): 1600090.

Authors : Andrea Ciavatti12, Roberto Sorrentino3, Laura Basiricò12, Bianca Passarella3, Mario Caironi3, Annamaria Petrozza3, Beatrice Fraboni12
Affiliations : 1Department of Physics and Astronomy, University of Bologna, Italy; 2National Institute for Nuclear Physics - INFN section of Bologna, Italy; 3Center for Nano Science and Technology@PoliMi, Istituto Italiano di Tecnologia;

Resume : Metal halide perovskites are rapidly emerging as active materials in low-cost high-performing optoelectronic devices. The success is driven by their long carrier diffusion lengths, low trap densities, high mobilities and low-temperature solution-processability that combine the high performance of traditional inorganic semiconductors with the low-cost, large area scalable, printing technologies typical of organic semiconductors. The presence of heavy atoms and the high crystal density make them ideal for direct detection of ionizing radiation. Despite top performance of perovskite single crystal detectors, they do not fully exploit the solution processability on flexible plastic substrates. Up to now, flexible direct X-ray detectors have been developed employing mainly organic materials and few preliminary results have been reported on thin-film perovskite-based X-ray detectors [1]. We develop a direct X-ray detector based on the photo-conducting properties of printed micrometers-thick film of methylammonium lead triiodide (MAPbI3) microcrystals, passivated with an organic layer of PCBM. The processing and deposition methods here employed allow to target the possibility of scaling-up the process with large-area compatible techniques, thanks both to the ease of print of the active material on different kind of substrates and to the synthesis methods, that strongly exclude high boiling point- and toxic-organic solvents, here replaced by benign solvents. We used the bar coating printing technique that, by realizing multiple depositions, permitted us to obtain deposited films of tunable thickness up to tens of microns, maximizing the film thickness to enhance radiation absorption, while maintaining a good layer uniformity and high electrical performance [2]. The devices showed limited hysteresis, stability in time and good radiation hardness over total dose of several Grays. The X-ray response is sharp, repeatable over multiple cycles and scales with the bias. The photocurrent increment (ION - IOFF) is linear with the impinging dose rate in the tested X-ray energy range above, thus demonstrating the capability of the detectors to be employed as reliable real-time direct dosimeters under a wide X-ray energy range (40 ? 150 kVp) and for a wide dose rate range, spanning from µGy/s to mGy/s. The sensitivity reaches the remarkable top value of 2270 µC Gy-1 cm-2. The here reported sensitivity is the highest value among all the films, perovskite-based, which are compatible with large area and flexible substrates. Noteworthy, such high sensitivity values are competitive also with others high performing perovskite-based detectors that generally have much thicker active layer. Time response of 40 ms and limit of detection results comparable with the typical values reported for polycrystalline perovskite films [3]. [1] S. Yakunin et al., Nat Photon, 9, 7, 444?449 (2015). [2] V. Venugopalan et al, Chem (2019), 5, 868. [3] A. Ciavatti et al, Adv. Func. Mat (2021), doi: 10.1002/adfm.202009072

16:15 DISCUSSION    
Charge transport, structure-function V : Simone FABIANO
Authors : Mario Caironi
Affiliations : Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Via Pascoli 70/3, 20133 Milano, Italy

Resume : In this contribution I first set a framework for plausible applications of thermal to electrical energy conversion, where low power applications appear to be at present one of the most interesting cases. In fact, micro energy harvesters are becoming more and more relevant as energy resources for distributed low power electronics and sensors networks. In this context, micro thermoelectric generators (µTEG) possess many advantages, as they can work in the dark and require limited maintenance. Ideally, such µTEGs should be cost effective and based on abundant materials. Organic conjugated materials have been studied to address such requites, as they can enable lightweight, flexible and cost competitive µTEGs produced through mass scaled printing techniques. In this context, I report on our studies on doping of polymer semiconductors, aimed at understanding and overcoming the limits in thermoelectric properties. Then, I focus on a new organic, flexible µTEG where doped p-type and n-type organic semiconductors are inkjet printed to form a micro module composed of 128 thermocouples on plastic. In particular, the architecture is specifically devised to improve the thermal coupling and simplify the fabrication process. Such device allows to envisage future efficient devices delivering µW/cm2 close to room temperature and at low temperature differences.

Authors : Bedolla-Valdez, Z. I. (a) , Gonel, G., Saska, J. (a) , Shevchenko, N. E. (b), Ghosh, R. (c), Cendra-Guinassi, C. A. (d) , Zhang, F. (e) , Jacobs, I. E. (f) , Murrey, T. L. (a) , Fergerson, A. (a), Aronow, S. D. (b) , Dudnik, A. S. (b) ,Kahn, A. (e) , Salleo, A. (d) , Spano, F. C. (c) , Mascal, M. (b) , Moule, A. J. (a)
Affiliations : (a) University of California, Davis - Department of Chemical Engineering (b) University of California, Davis - Department of Chemistry (c) Temple University - Department of Chemistry (d) Stanford University - Department of Materials Science (e) Princeton University - Department of Physics

Resume : Molecular doping of conjugated polymers has attracted focused attention because they can yield excellent optical, electronic, and thermoelectric properties. In particular, there has been focus on understanding how the relative location/orientation between the polymer semiconductor and molecular dopant affect both the local and bulk materials properties. Here we present a detailed study of sequentially doped thiophene films with a range of ionization energies using a series of chemically similar molecular dopants with a range of electron affinities. Using optical and conductivity measurements, we show that stronger dopants yield more free charges at low doping levels. Once a maximum density of ?free holes? is achieved, further doping increases the polaron absorbance, but does not yield an increased conductivity. Conductivity in the range of 10-100 S/cm are demonstrated for a series of thiophene and alternating thiophene/DPP polymers. We also quantify doping level and conductivity in a series of P3AT/F4TCNQ samples and show how changes in the side chain length, MW, PDI, and regio-regularity affect the availability of doping sites. All of the doping level assignments are thermodynamically consistent with a Langmuir isotherm model and quantum mechanically consistent with fits to the polaron states measured in the NIR.

Authors : D. R. Maslennikov [1], M. V. Vener [2], O. D. Parashchuk [2,3], O. G. Kharlanov [2,3], D. I. Dominsky [2,3], I. Yu. Chernyshov [2,3], D. Yu. Paraschuk [2,3], A. Yu. Sosorev [2,3]
Affiliations : [1] Department of Chemistry, Imperial College London, 80 Wood Ln, Shepherd's Bush, London W12 0BZ, UK [2] Institute of Spectroscopy of the Russian Academy of Sciences, Fizicheskaya Str., 5, Troitsk, Moscow 108840, Russia [3] Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia

Resume : Charge transport in high-mobility organic semiconductor crystals (OSCs) is limited by the non-local electron-phonon interaction (NLEPI) ? modulation of charge transfer integrals by low-frequency vibrational modes. However, experimental assessment of NLEPI, which could strongly promote an adequate description of charge transport in OSCs and provide a reliable prediction of their charge mobility, is still lacking. Here, using the example of two naphthalene diimide derivatives, we show that low-frequency Raman spectroscopy directly probes NLEPI in these organic semiconductors, and that the theoretical Raman spectra reasonably reproduce the experimental frequencies, intensities, and anisotropy of Raman in a full frequency range. Finally, we show how NLEPI affects calculated electron mobility and its anisotropy in the studied crystals. We anticipate that our findings will improve understanding of the charge transport mechanism in high-mobility organic semiconductors and guide the search for efficient organic electronics materials. Acknowledgements: This work was supported by the Russian Science Foundation, project ? 18-72-10165. Presenting author acknowledge funding by the President?s PhD Scholarships.

Authors : Nurlan Tokmoldin, Joachim Vollbrecht, Seyed Mehrdad Hosseini, Bowen Sun, Lorena Perdigón-Toro, Han Young Woo, Yingping Zou, Dieter Neher, Safa Shoaee
Affiliations : Nurlan Tokmoldin, Joachim Vollbrecht, Seyed Mehrdad Hosseini, Bowen Sun, Safa Shoaee: Optoelectronics of Disordered Semiconductors, Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Straße 24-25, Potsdam-Golm 14476, Germany; Lorena Perdigón-Toro, Dieter Neher: Soft Matter Physics, Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Straße 24-25, Potsdam-Golm 14476, Germany; Han Young Woo: Department of Chemistry, College of Science, Korea University, 145 Anam?ro, Seongbuk?gu, Seoul, 02841 Republic of Korea; Yingping Zou: College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, P.R. China

Resume : We present a simple approach to determine the vertical lifetime-mobility product for different carrier densities in a wide range of photovoltaic devices ? including 16% PM6:Y6 and higher-performance perovskite solar cells ? using steady-state photoconductance measurements and utilize this approach to obtain the in-device specific (long range) carrier drift and diffusion lengths in the studied systems. It is shown that these effective drift and diffusion lengths are closely related to the established fill-factor figures of merit, ? and ?, providing a straightforward way of determining these parameters in complete devices and under operating conditions. Finally, the relative diffusion length on its own is shown to provide good correlation with the device fill-factors for the diversity of the studied devices.


Symposium organizers
Christian NIELSENQueen Mary University of London

School of Biological and Chemical Sciences, Mile End Road, London E1 4NS, UK

+44 20 7882 5902
Daniele FAZZI (Main)University of Cologne

Institute of Physical Chemistry, Luxemburger Str. 116, D - 50939 Cologne, Germany

+49 221 470 3279
Simone FABIANOLinköping University

Department of Science and Technology, SE-60174 Norrköping, Sweden

+46 11363633
Sophia C. HAYESUniversity of Cyprus

Department of Chemistry, P.O. Box 20537 1678, Nicosia, Cyprus

+357 22 892769