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Bio- and soft materials

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Advanced characterization of organic and hybrid materials

Understanding the doping and charge transport in organic semiconductors and hybrid perovskites is far from trivial due to the complex interplay between structure and optoelectronic properties. Therefore, it requires developing advanced and novel characterization techniques, which are the focus of the present symposium.

Scope:

Past research on conjugated organic materials (COMs) and organic-inorganic hybrid perovskite materials (OHPMs) revealed that understanding the fundamental physical processes in such materials often requires significantly adapting concepts which are otherwise well-established in inorganic semiconductor physics. Key phenomena such as doping related charge transfer, charge transport, exciton generation and dissociation as well as the role of anisotropy and microstructure are currently intensively studied and still not fully explained today. Increasing our understanding of these phenomena is, however, of utter importance both for fundamental science and any future application of COMs and OHPMs in novel technology based thereon. Clearly, this requires advanced characterization techniques to be developed and tailored to the particularities of these materials, both in experiment and theoretical modeling. The present symposium aims at stimulating an interdisciplinary discourse on advanced characterization techniques for COMs and OHPMs by bringing together current theoretical and experimental standpoints from physics, chemistry, and materials science. It further strives to discuss new developments, challenges, and perspectives in this field which arise from these techniques. The symposium addresses (but is not limited to) advanced characterization techniques that target structural, electronic, phononic, electrical, and thermoelectrical properties both theoretically and experimentally. A special focus lies on experimental techniques as performed at large scale research facilities such as synchrotron radiation sources and on the role of novel approaches in material science based on machine learning.

Hot topics to be covered by the symposium:

  • Interface and bulk doping in conjugated organic materials and hybrid perovskites
  • Charge-transfer processes at organic and hybrid heterojunctions
  • Structural, electrical and electronic characterization of interfaces and thin films
  • Characterization of thermoelectric properties
  • Phononics in organic and hybrid materials
  • Anisotropy in doped organic semiconductor systems
  • Charge transport in organic or perovskite two- and three-terminal devices
  • Advanced spectroscopic and microscopic techniques
  • Novel experimental techniques using synchrotron radiation
  • Theoretical modelling of doping, charge transfer and transport
  • Machine learning in material science of organic materials and hybrid perovskites
  • Novel applications and their performance characterization

List of invited speakers:

  • Oliver Fenwick, QMUL, UK
  • Alberto Salleo, Stanford University, USA
  • Sophia Hayes, University of Cyprus, Cyprus
  • Henning Sirringhaus, University of Cambridge, UK
  • Anne Guilbert, Imperial College London, London, UK
  • Elizabeth von Hauff, University of Amsterdam, The Netherlands
  • Lay Lay Chua, National University of Singapore, Singapore
  • Satoshi Kera, Institute for Molecular Science, Japan
  • Andrew Musser, Cornell University, USA
  • Anna Köhler, University of Bayreuth, Germany
  • Carlos Silva, Georgia Tech, USA

Tentative list of scientific committee members:

  • Natalie Stingelin (Georgia Tech, USA)
  • Silvia Milita (CNR, Bologna, Italy)
  • Prof. Yves Geerts (Université Libre de Bruxelles, Belgium)
  • Mirko Cinchetti (University of Dortmund, Germany)
  • Norbert Koch (Humboldt Universtät zu Berlin, Germany)
  • Nobuo Ueno (Chiba University, Japan)
  • Egbert Zojer (TU Graz, Austria)
  • Luca Muccioli (University of Bologna, Italy)
  • Jérôme Cornil (University of Mons, Belgium)
  • Iain McCullough (Imperial College London, UK, and KAUST, Saudi Arabia)
  • Thomas Anthopoulos (KAUST, Saudi Arabia)
  • Marta Mas-Torrent (ICMAB, Spain)

Documentation

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08:45 Welcome and Introduction to the Symposium    
 
Doping phenomena I : Natalie Banerji - Steffen Duhm
09:00
Authors : Henning Sirringhaus
Affiliations : Cavendish Laboratory, University of Cambridge

Resume : Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counter-ions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique based on ion exchange, we prepare highly doped films with several counter-ions of varying size and shape, and characterize their carrier density, electrical conductivity, and paracrystalline disorder. In this uniquely large dataset composed of several classes of high mobility conjugated polymers each doped with at least 5 different ions, we find electrical conductivity to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parameterized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localisation theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disorder-limited nature of charge transport and suggesting new strategies to further improve conductivities and thermoelectric properties.

U.1.1
09:30
Authors : Priscila Cavassin, Isabelle Holzer, Olivier Bardagot, Julien Réhault, Natalie Banerji
Affiliations : University of Bern

Resume : Recently, conjugated polymers that exhibit mixed electronic and ionic conduction have been largely explored for a wide range of applications, from biological sensing and stimulation to supercapacitors and batteries.[1] A relevant property of these materials is their ability to be electrochemically doped. This process relies on the injection of ions from an electrolyte into the film. The ions interact with the polymer chains creating charged species, such as polarons and bipolarons, increasing the materials conductivity in several orders of magnitude. Due to the increasing number of applications that rely on this process, there has been great interest in further understanding its properties and fundamental mechanisms.[2] In this work, we study the impact of the polymer film morphology on the electrochemical doping. We use time-resolved visible-near infrared (Vis-NIR) and Raman spectroscopy to show that the ordered and disordered domains of poly(3-hexylthiophene) (P3HT) are doped through different mechanisms and kinetics. We demonstrate that for intermediate doping levels, polarons and bipolarons coexist exclusively in the disordered domains. In the ordered domains, only polarons are formed until there are no more ordered undoped chains. At this point, part of the polarons start to be converted into bipolarons. Furthermore, we show that the kinetics is also different for each domain, the ordered one being doped faster than the disordered for all doping levels. Based on these observations, we propose the steps involved in the doping of both morphological domains of P3HT To confirm our propositions, we used electrochemical Raman spectroscopy, which is a technique that is very sensitive to the structural changes the polymer undergoes during doping. We obtained good agreement with the trends observed with Vis-NIR spectroscopy. Finally, we compared the doping of P3HT films with different degrees of morphology. We use regiorandom P3HT to investigate the doping in purely disordered films, and the results strongly correlate with our proposed mechanism. [1] B. D. Paulsen, K. Tybrandt, E. Stavrinidou, J. Rivnay, Nature Materials 2020, 19, 13-26. [2] E. M. Thomas, M. A. Brady, H. Nakayama, B. C. Popere, R. A. Segalman, M. L. Chabinyc, 2018, Advanced Functional Materials 2018, 28, 1803687

U.1.2
09:45
Authors : Demetra Tsokkou, Priscila Cavassin and Natalie Banerji
Affiliations : Department of Chemistry, Biochemistry and Pharmacy (DCBP), University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.

Resume : Doping is an efficient method to significantly increase the conductivity of otherwise insulating organic materials. Despite that this field has been studied for years, recently it attracted significant fundamental and applied scientific interest due to the potential to integrate such systems in a variety of low-cost electronic (i.e. solar cells, transistors, light-emitting diodes) and more recently bioelectronic devices (i.e. biosensors). This has been facilitated by recent advances in synthetic methods and improved material characteristics. However, awareness must be raised on the understanding of the fundamental processes leading to the formation of conductive charges and especially the role bipolarons that have been less studied. Here, we access the short-range transport properties and doping mechanisms in electrochemically doped P3HT, where its doping level is modified by changing the applied oxidation potential. Electrochemistry offers controllable doping level; reversibility of the doping/dedoping processes; and high charge carrier concentrations at low operating voltages. We use a combination of optical methods, such as in situ THz spectroscopy and spectro-electrochemistry and we relate the nature and density of the charged species (polarons and bipolarons) with the polymer short-range conductivity. We show that the co-existence of polarons and bipolarons in electrochemically doped P3HT is essential to maximize the polymer conductivity, which allows a high concentration of carriers to participate in transport via mixed-valence hopping. D. Tsokkou , P. Cavassin , G. Rebetez and N. Banerji, Bipolarons rule the short-range terahertz conductivity in electrochemically doped P3HT, Mater. Horiz., 2022, 9, 482-491

U.1.3
10:00
Authors : Hannes Hase, Michael Berteau-Rainville, Somaiyeh Charoughchi, Wolfgang Bodlos, Roland Resel, Emanuele Orgiu, Ingo Salzmann
Affiliations : Department of Physics, Concordia University, Montreal, Canada; Institut national de la recherche scientifique (INRS), Varennes, Canada; Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada; Institute of Solid State Physics, TU Graz, Graz, Austria, and Materials Science and Engineering, Stanford University, Stanford, California 94305, USA; Institute of Solid State Physics, TU Graz, Graz, Austria; Institut national de la recherche scientifique (INRS), Varennes, Canada; Department of Physics, Department of Chemistry and Biochemistry, Centre for Research in Molecular Modeling (CERMM), and Centre for NanoScience Research (CeNSR), Concordia University, Montreal, Canada

Resume : Molecular doping allows increasing the conductivity of organic semiconductors. Upon doping, the formation of (spatially separated) ion pairs (IPAs) and charge-transfer complexes (CPXs) have been identified as the two competing phenomena to occur, where the former is desired to promote the generation of mobile charge-carriers in the semiconductor host. In general, high electron affinity (EA) of the acceptor versus the ionization energy (IE) of the donor is favourable to IPA occurrence, where IE-EA is commonly used as a predictor to IPA formation. In contrast, coupling between the frontier molecular orbitals of dopant and semiconductor promotes CPX formation. Here, we investigate these phenomena for the p-type doping of the conjugated polymer poly(3-hexylthiophene) (P3HT) with tetracyanoquinodimethane derivatives of increasing degree of fluorination (FxTCNQ, x = 0,1,2,4), which translates into increasing electron affinities. Along conductivity measurements and grazing-incidence X-ray diffraction, we employ optical and vibrational absorption spectroscopy to characterize the host-dopant interactions. We find that all dopants show CPX formation and, additionally, the stronger dopants F4TCNQ, F2TCNQ, and FTCNQ show IPA occurrence. This observation is more pronounced for F4TCNQ and, in general, lower dopant loading. Cyclic voltammetry confirms that only the EA of F4TCNQ exceeds the IE of P3HT, while TCNQ, FTCNQ, and F2TCNQ have significantly lower EA values, all of which are broadly similar. This poses the questions of (i) why FTCNQ and F2TCNQ clearly show IPA formation despite apparently unfavourable energetics and (ii) why TCNQ, despite having similar EA, exclusively shows CPX formation. To approach these questions, we employed a semi-classical modelling approach to determine the percentage of ionized dopants in the P3HT matrix by varying the width of the density of states (DOS) assuming a Gaussian distribution for the highest occupied molecular orbital of P3HT. We then compared the results with the experimental percentage of dopant ionization estimated from the relative magnitude of the FxTCNQ C?N stretch modes in our vibrational spectra. Being cautious with the interpretation of these vibrational bands as they are highly sensitive to the solid-state packing, we can still conclude on a dopant-dependent broadening of the DOS. While for TCNQ-doping its width is in line with the recently reported values for pure P3HT, the occurrence of IPA with the fluorinated dopants can be understood as a result of a DOS broadening by a factor of four, which is in line with previous studies on charge transport suggesting doping-induced and dopant-dependent disorder in the P3HT matrix.

U.1.4
10:15 Discussion    
10:30 Break    
 
Advanced Microscopies I : Roland Resel
11:00
Authors : Giovanni Costantini
Affiliations : Department of Chemistry, University of Warwick

Resume : In this talk I will demonstrate that high resolution scanning probe microscopy is capable of delivering crucial information ? that cannot be achieved by any other current analytical method ? about ?real world? energy materials with a huge practical and technological relevance. In particular, I will show that by combining vacuum electrospray deposition (ESD) and high-resolution scanning tunnelling microscopy (STM) it is possible to image conjugated polymers used in organic electronics and photovoltaic devices with unprecedented details. Based on this, it becomes possible to sequence the polymers by visual inspection and to determine their molecular mass distribution by simply counting the repeat units. Moreover, I will demonstrate that we can precisely determine the nature, locate the position, and ascertain the number of synthetic defects in the polymer backbone [1-2]. The analysis of our high-resolution images univocally demonstrates that one of the main drivers for backbone conformation and polymer self-assembly is the maximization of alkyl side-chain interdigitation. On this basis, we investigate the 2D assembly of a series of conjugated polymers with the aim of gaining insight in the molecular microsctructure of the corresponding 3D functional thin films [3,4]. References 1. D.A. Warr, et al., Sci. Adv. 4, eaas9543 (2018). 2. M. Xiao, et al., Adv. Mater. 32, 2000063 (2020). 3. H. Chen, et al., J. Am. Chem. Soc. 141, 18806 (2019). 4. R.K. Hallani, et al., J. Am. Chem. Soc. 143, 11007 (2021).

U.2.1
11:30
Authors : Wen-Shan Zhang, Rasmus R. Schröder
Affiliations : Centre for Advanced Materials, Universität Heidelberg & Bioquant, Univeristy Hospital Heidelberg, D-69120 Heidelberg, Germany

Resume : Research in organic optoelectronic devices is expanding at an unprecedented rate and organic semiconductors are being applied in a wide range from transistors, integrated circuits, flexible displays, biosensors, to many other cost-effective green devices in ways not possible with conventional inorganic semiconductors. Among these, one of the key properties for realizing high-performing devices is a good charge-carrier mobility. Generally, this value is obtained from organic thin-film transistors (OTFTs) built with the desired organic semiconductors as the active material. The measured mobility is, however, a material- and also device-dependent value and does not necessarily allow to draw a direct conclusion on the charge transport ability of the material itself. Thin-film morphology and device structure employed can lead to a significant variation of the experimentally acquired charge-carrier mobility. By using an ultra-low voltage scanning electron microscopy (Delta-SEM) [1,2], we have developed an imaging method to eliminate the influence of non-ideal morphology and we were able to achieve a reproducible mobility number based on well-built OFTF devices.[3] Furthermore, we would like to directly estimate the charge transport ability regardless of the quality of the thin-film morphology. Using the Delta-SEM we are able to record the spatially resolved energy spectrum of the secondary electrons (SEs, < 50 eV). Mapping of the peak position of the SE energy spectrum allows us to reveal the dynamic surface potential (DSP) distribution on the semiconductor during the exposure to the electron beam. According to the variation of the DSP map under different parameters such as beam energy, beam current, dwell time and manification etc., we are able to assign the charge-carrier mobility within an order of magnitude. This established method can be used to examine the charge transport ability directly from the as-synthesized materials, regardless of their size (µm-crystallites are applicable) and saving the expense of device fabrication. It will help us to draw a correct structure-property relationship and furthermore, help to design rationally novel materials towards higher performance. References: 1. Steigerwald, M. et al. Frontiers of Characterization and Metrology for Nanoelectronics 51-55 (2013). 2. Schroder, R. R. et al. Microsc. Microanal. 24, 626-627 (2018). 3. Zhang W.-S. et al, Adv. Electron. Mater.7, 2100400 (2021)

U.2.2
11:45
Authors : Alexander Ebner, Paul Gattinger, Ivan Zorin, Christian Rankl, Markus Brandstetter
Affiliations : RECENDT ? Research Center for Non-Destructive Testing GmbH, Linz, 4040, Austria; RECENDT ? Research Center for Non-Destructive Testing GmbH, Linz, 4040, Austria; RECENDT ? Research Center for Non-Destructive Testing GmbH, Linz, 4040, Austria; RECENDT ? Research Center for Non-Destructive Testing GmbH, Linz, 4040, Austria; RECENDT ? Research Center for Non-Destructive Testing GmbH, Linz, 4040, Austria

Resume : Hyperspectral imaging (obtaining a spectrum for each pixel in an image) combines spectroscopy methods with spatially resolving optics and thus enables non-destructive and label-free chemical imaging. Although it is already widely used, e.g. in food processing, agriculture or mineralogy, most devices currently operate in the visible or near-infrared spectral range due to the availability of low-cost detectors. In contrast to that, the mid-infrared (MIR) spectral range ? which probes specific phonons and molecular vibrations ? offers drastically improved chemical sensitivity and detection limits. However, the typically high price of MIR components ? particularly of MIR line or array detectors ? prevents this technology from emerging to a broad field of potential applications. In order to tackle these limitations, we present a first demonstration of hyperspectral MIR microscopy based on a single-pixel imaging (SPI) approach using a digital micromirror device (DMD) modified for the MIR. The applied DMD not only enables SPI by subsequentially masking the captured scene, it also disperses the projected images due to diffraction at the micromirrors and thus allows for wavelength selection without additional dispersive elements. In addition, the developed microscope employs an MIR supercontinuum source (1.55 µm ? 4.5 µm) for broadband sample illumination. A detailed characterization of the spectral and spatial resolution is presented. Furthermore, the sufficiency of the realized spectral resolution of up to 162 nm is demonstrated by the investigation of polymer multilayer structures. By means of Hadamard sampling, 64×64 images can be acquired and reconstructed in 450 ms and 162 ms, respectively. Since the presented approach provides fast MIR hyperspectral imaging with a tunable field of view and tunable spatial resolution, sample throughput in chemical and phononic imaging can be drastically improved.

U.2.3
12:00 Discussion    
12:15 Lunch Break    
 
Doping phenomena II : Ingo Salzmann
13:45
Authors : Gabriele D'Avino
Affiliations : Grenoble Alpes University, CNRS, Grenoble INP, Institut Ne?el, 25 rue des Martyrs, 38042 Grenoble, France

Resume : Molecular doping is arguably the main technique to control charge carriers? density and transport properties in organic semiconductors, enabling a large variety of technological applications from optoelectronics to thermoelectricity. This contribution reports on our multiscale modelling research efforts towards a comprehensive understanding of the mechanism of molecular doping from infinite dilution to high densities. Our message is threefold: (i) We shed light onto the factors controlling the energetics of the ionization of dopants, with specific emphasis on the role of environmental electrostatic interactions. Our calculations disclose how dopants' impurity levels strongly depend on the host material, or on the exact position of the dopant inside a given material. [1] (ii) We unveil the effect of collective dielectric screening phenomena sourced from highly-polarizable host-dopant complexes, that we predict playing a leading role in the release of Coulombically bound carriers upon increasing density, as the system approaches a dielectric catastrophe with the transition to a conducting state. [2] (iii) We finally address the high-doping regime in ion-exchange doped polymers, for which we propose a quantum model, fully accounting long-range Coulomb interactions and energetic disorder. This predicts charge transport to be essentially limited by disorder, rather than by Coulomb interactions with ionized dopants, rationalizing state-of-the-art experiments on a broad set of polymers and dopant ions. [3] [1] Li et al., Materials Horizons 6, 107 (2019); Comin et al., in preparation. [2] Comin, Fratini, Blase, D?Avino, Advanced Materials (2022); doi: 10.1002/adma.202105376 [3] Jacobs, D?Avino et al., J. Am. Chem. Soc. (2022); doi: 10.1021/jacs.1c10651

U.3.1
14:15
Authors : Alberto Privitera(1), Giacomo Londi(2), Moritz K. Riede(1), Gabriele d'Avino(3) and David Beljonne(2)
Affiliations : (1) Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU UK (2) Laboratory for Chemistry of Novel Materials, University of Mons, Mons, B-7000 Belgium (3) Institut Néel, CNRS and Grenoble Alpes University, Grenoble, F-38042 France

Resume : In this work[1] we investigate the role of local environmental interactions on the generation of free charge carriers in doped organic layers. By means of a classical microelectrostatic model, a dual effect of molecular quadrupole moments of host and dopant molecules on doping is demonstrated in doped binary (ZnPc:F6-TCNNQ and F8ZnPc:F6-TCNNQ) and ternary (ZnPc:F8ZnPc:F6-TCNNQ) blend. Based on an in-depth atomistic modelling of electrostatic and dielectric phenomena in molecular solids, we show that charge-quadrupole interactions affect both the ionization step (by reshuffling the energy levels of the dopant and the host) and the charge dissociation one (by creating a favourable energy pathway for the hole). In addition to long-range electrostatics characterizing the energy landscape of ordered molecular films, we observe that the replacement of a host molecule with F6-TCNNQ has a significant short-range effect, namely the ionization potential (IP) of the host molecules next to a dopant impurity strongly differ (up to 0.4 eV) from the IPs of the host molecules further away. This electrostatic contribution is due to the difference in quadrupole moment between F6-TCNNQ and the host molecules, and it significantly affects the host-dopant gap, which, on average, amounts to 0.63 eV for ZnPc and 0.86 eV for F8ZnPc. When accounting for screened electron-hole Coulomb interactions, we find an overall energy barrier that is close to zero for the ionization step in a binary ZnPc:F6-TCNNQ blend, while in F8ZnPc:F6-TCNNQ this barrier is 0.2 eV larger. Most interestingly, the explicit calculation of the energy profile for charge separation reveals that the quadrupole moments of dopant impurities can positively impact this crucial process. [1] Adv. Funct. Mater. 2020, 30, 2004600

U.3.2
14:30
Authors : Pingping JIANG (1), Boubacar TRAORE (2), Mikael KEPENEKIAN (2), George VOLONAKIS (2), Claudine KATAN (2), Laurent PEDESSEAU (1), and Jacky EVEN (1)
Affiliations : (1) Univ Rennes, INSA Rennes, CNRS, Institut FOTON - UMR 6082, F-35000 Rennes, France (2) Univ Rennes, ENSCR, INSA Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes) - UMR 6226, F-35000 Rennes, France

Resume : To cope with the toxicity of Pb-based perovskites and achieve smaller electronic band gaps, replacing Pb with Sn has gained growing attention recently 1,2. Importantly, the low-bandgap Pb-Sn alloyed perovskite allows building all-perovskite tandem solar cells that shall overcome the performances of single-junction perovskite cells 3,4. The surface and interface functionalizations after the assembly with charge transport layer (CTL) remain one of the most critical parameters 5,6. In view of the sophisticated chemical and physical properties of Sn-based perovskites, theoretical calculations based on density functional theory (DFT) have been employed to model the interplay between absorbers and CTLs. In order to understand the fundamental physicochemical mechanisms of that interplay, we have chosen FASnI3 as the benchmark material and thoroughly investigated the influence of its surface termination on structural and electronic properties at interfaces with CTL, including intermediate work function calculations on free-standing slabs. Based on the theoretical paper of our team7, we have evidenced the proportional relationship between the work function and the surface dipole, making the optimization of interfacial charge transport possible by surface dipole tuning. Our findings contribute to discovering other promising alternatives as CTLs for Pb-free perovskites in the light of surface and interface engineering. This DROP-IT project8 has received funding from the European Union?s Horizon 2020 research and innovation Program under the grant agreement No 862656. The information and views set out in the abstracts and presentations are those of the authors and do not necessarily reflect the official opinion of the European Union. Neither the European Union institutions and bodies nor any person acting on their behalf may be held responsible for the use which may be made of the information contained herein. 1. Li, J. et al. Review on recent progress of lead-free halide perovskites in optoelectronic applications. Nano Energy 80, 105526 (2021). 2. Dong, Q. et al. Electron-hole diffusion lengths>175 ?m in solution-grown CH3NH3PbI3 single crystals. Science 347, 967?970 (2015). 3. Jiang, T. et al. Realizing High Efficiency over 20% of Low?Bandgap Pb?Sn?Alloyed Perovskite Solar Cells by In Situ Reduction of Sn 4+. Sol. RRL 4, 1900467 (2020). 4. Lin, R. et al. Monolithic all-perovskite tandem solar cells with 24.8% efficiency exploiting comproportionation to suppress Sn(ii) oxidation in precursor ink. Nat Energy 4, 864?873 (2019). 5. Shao, S. & Loi, M. A. The role of the interfaces in perovskite solar cells. Adv. Mater. Interfaces 7, 1901469 (2020). 6. Lin, R. et al. All-perovskite tandem solar cells with improved grain surface passivation. Nature (2022) doi:10.1038/s41586-021-04372-8. 7. Traoré, B. et al. A Theoretical Framework for Microscopic Surface and Interface Dipoles, Work Functions, and Valence Band Alignments in 2D and 3D Halide Perovskite Heterostructures. ACS Energy Lett. 7, 349?357 (2022). 8. DROPIT. https://www.uv.es/dropit/.

U.3.3
14:45 Discussion    
15:00 Break    
 
Session 4: Photophysics I : Emanuele Orgiu
15:30
Authors : Ziyuan Ge(1), Ben P. Carwithen(1), Martin Kroll(2), Thomas R. Hopper(1), Karl Leo(2), Yana Vaynzof(2), Artem A.Bakulin(1*)
Affiliations : (1). Department of Chemistry and Centre for Processable Electronics, Imperial College London, W12 0BZ, United Kingdom (2). Centre for Advancing Electronics Dresden, Technische Universität Dresden, 01069 Dresden, Germany

Resume : Lead-halide perovskites (LHPs) are widely researched for their unique optoelectronic properties and facile synthesis routes. 2D perovskites have now been developed which possess tunable energy states, and better stability than their bulk counterparts. LHPs have been found to possess a longer hot carrier cooling (HCC) time compared to conventional semiconductors, e.g. GaAs, owing to their more pronounced hot phonon bottleneck, which could further lend to the emergence of the hot carrier solar cell. An accurate estimation of the HCC time is therefore vital in terms of guiding device design and optimization. HCC dynamics are typically studied by extracting the time-evolving carrier temperature from broadband transient absorption spectra. However, the excitonic character of 2D perovskites may complicate this approach. Herein, we applied the pump-push-probe technique to isolate the hot carrier cooling process in zone-cast (ZC) and drop-cast (DC) films of the Ruddlesden-Popper 2D perovskite (PEA)2PbI4. We then examined the dependence of HCC time on increasing numbers of hot carriers and found a negligible hot phonon bottleneck effect for both the ZC and DC films, but with a longer, intrinsic cooling time compared to the bulk perovskites. These observations may be explained by the reported dielectric-confinement found in the 2D systems.

U.4.1
15:45
Authors : Andrew Musser
Affiliations : Cornell University

Resume : The hybrid light-matter character of exciton-polaritons enables strikingly long-range energy transport in organic materials. This is typically determined through steady-state spatial mapping, with little investigation of the transport dynamics. In particular, organic polariton propagation in has not been probed in the initial coherent regime, where photon and exciton wavefunctions are inextricably mixed. Hence key mechanistic questions remain poorly understood: What structural properties determine transport velocity and range? What is the role of intracavity dark states? Here, we use femtosecond transient absorption microscopy to directly image coherent polariton motion in microcavities of varying quality factor, an approach that allows us to circumvent the challenges of disentangling polariton signatures from optical artefacts. We find the transport to be well-described by a model of band-like propagation of an initially Gaussian distribution of exciton-polaritons in real space. The velocity of the polaritons reaches values of ~0.65 × 10^6 m s-1, substantially lower than expected from the polariton dispersion. Surprisingly, we find that the velocity is proportional to the quality factor of the microcavity. We suggest the unexpectedly slow coherent transport and this link between quality-factor and polariton velocity to reflect an ultrafast interplay between delocalised dark states and the polaritons. Our results demonstrate the important role that intracavity dark states play even within the coherent regime and reveal a new lever to control polariton transport.

U.4.2
16:15 Discussion    
16:30 Break    
 
Poster Session : Ingo Salzmann
16:45
Authors : Manuela Schiek (1), S. Funke (2), M. Duwe (2), P.H. Thiesen (2), K. Hingerl (1), F. Balzer (3)
Affiliations : (1) Johannes Kepler University of Linz, Austria; (2) Accurion GmbH Göttingen, Germany; (3) University of Southern Denmark, DK

Resume : Imaging Mueller matrix ellipsometry combines the power of variable angle spectroscopic ellipsometry and optical microscopy mapping. Here we analyze squaraine thin film samples crystallizing in an orthorhombic phase, which are subdivided into micro-sized rotational domains with a single crystallographic orientation parallel to the substrate. Combined multiple ROI analysis of rotational scans at fixed wavelength and spectroscopic reflection/transmission scans allows the determination of the full diagonal dielectric tensor, which reproduces well the Davydov splitting of the material. [1] Funke, Duwe, Balzer, Thiesen, Hingerl, Schiek. J. Phys. Chem. Lett. 19 (2021) 3053.

U.5.1
16:45
Authors : Yang, C.-Y.(1), Stoeckel, M.-A.*(1), Ruoko, T.-P.(1), Wu, H.-Y.(1), Liu, X.(1), Kolhe, N.B.(2), Wu, Z.(3), Puttisong, Y.(4), Musumeci, C.(1), Massetti, M.(1), Sun, H.(1), Xu, K.(1), Tu, D.(1), Chen, W.M.(4), Woo, H.Y.(3), Fahlman, M.(1), Jenekhe, S.A.(2), Berggren, M.(1), Fabiano, S.(1)
Affiliations : (1) Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, Sweden (2) Department of Chemical Engineering and Department of Chemistry, University of Washington, Seattle, WA, USA (3) Department of Chemistry, College of Science, Korea University, Seoul, 136-713, Republic of Korea (4) Department of Physics, Chemistry and Biology, Linköping University, Linköping, Sweden

Resume : Conducting polymers are opening new possibilities that are impacting several technologies such as organic thermoelectrics but also opto- and bioelectronics applications. Among these polymers, PEDOT:PSS is the most successful one that can transport holes. With an electrical conductivity reaching thousands of S cm-1 and an exceptional ambient stability, this ionic/electronic conductor has been integrated in multiple applications spanning from conducting layers in organic solar cells or light-emitting diodes to active material in sensors and actuators, supercapacitors or thermoelectrics. The versatility of the synthesis and processing of PEDOT:PSS is another reason for its success, being compatible with large-scale deposition methods such as ink-jet printing or spray-coating, through an ink formulation that is water-based. However, while PEDOT:PSS only transports holes (p-type), several opto- and bioelectronic applications include devices that require the integration of materials for the transport of both charges; an n-type material able to transport electrons, combined with a p-type material that transport holes. To fill this gap, several n-type polymers were developed, without entirely reaching the performances of their p-type counterpart PEDOT:PSS. Most of these n-type conducting polymers, when properly doped, demonstrates electron conductivity of tens of S cm-1. However, their use at the industrial scale is extremely limited due to their processing involving halogenated solvents that are harmful to the environment. Moreover, they usually lack of ambient and thermal stability, and can be hardly overprocessed due to a poor solvent stability, resulting in mediocre performances. Diverse approaches are explored in order to enhance the electrical performances of this class of n-type materials, from design rationalizations and adjustments of the chemical structure to the careful choice of dopant. For instance, polymeric backbone planarization and increased rigidity is a strategy towards superior properties for high-performing conducting polymers. Here we report on the use of the rigid ladder-type electron-conducting polymer poly(benzimidazobenzophenanthroline) (BBL) composing an n-type conductive ink for printed electronics. The ink is alcohol-based and composed of nanoparticles of BBL produced from a solvent exchange process. This system is doped using the amine-based polymer poly(ethyleneimine) (PEI) and is processable by spray-coating in air. A thermal activation allows the BBL:PEI thin-film to demonstrate an electrical conductivity up to 8 S cm-1, with an excellent thermal stability. Interestingly, this film is stable even when washed with common organic solvents typically used for microfabrication. Finally, we employed this material as active layer in thermoelectric generators, and as ion-electron conductor in an organic electrochemical transistor (OECT) working in n-type depletion-mode regime that is the first of its kind.

U.5.2
16:45
Authors : Julia Marí-Guaita, Amal Bouich, Bernabé Marí
Affiliations : Institut de Disseny i Fabricació, Universitat Politècnica,València, Spain

Resume : Hybrid organic-inorganic perovskites (HOIPs) have been studied deeply in recent years due to their exceptional optoelectronic properties and correlated photovoltaic performance. In this work, we discuss the structural, morphological, and optical properties and the surface stability of Cs-based perovskite thin films by mixing Sn and Pb cations. On the one hand, Sn Cs-based perovskites have been a noted candidate to produce lead-free HOIP to avoid toxicity in the devices. Also, CsSnI3 demonstrated high PCE for solar cell application. However, the drawback of this kind of solar cell device is its instability and rapid degradation. On the other hand, Pb Cs-based perovskites are chosen as the absorber layer in solar cells due to their ideal bandgap which makes them outstanding candidates for PV performance. The handicap here is the environmental risks and impact on humans? health of lead. To conclude this work, we performed Sn-Pb mixed Cs-based perovskites to benefit from both cation types in the properties of the device and reduce the negative aspects of each one of them.

U.5.3
16:45
Authors : D. Brick, M. Hofstetter, F. Noll, P. Stritt, J. Rinder, V. Gusev, T. Dekorsy, M. Hettich
Affiliations : Department of Physics, University of Konstanz, 78464 Konstanz, Germany; Department of Physics, University of Konstanz, 78464 Konstanz, Germany; Research Center for Non-Destructive Testing GmbH, Altenbergerstr. 96, 4040 Linz, Austria; Department of Physics, University of Konstanz, 78464 Konstanz, Germany; Department of Physics, University of Konstanz, 78464 Konstanz, Germany; Laboratoire d'Acoustique de l'Université du Mans (LAUM), UMR 6613, Institut d'Acoustique - Graduate School (IA-GS), CNRS, Le Mans Université, Av. O. Messiaen, 72085 Le Mans, France; Institute of Technical Physics, German Aerospace Center, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany; Research Center for Non-Destructive Testing GmbH, Altenbergerstr. 96, 4040 Linz, Austria;

Resume : The measurement of the glass transition temperature in poly(methyl methacrylate) (PMMA) films by picosecond ultrasonics with thicknesses ranging from 458 nm to 32 nm is demonstrated . A shift of the longitudinal acoustic eigenmodes of the PMMA films towards lower frequencies with temperature is observed which is accompanied by a change in the temperature-frequency slopes at the glass transition temperature. The contributions of the change in thickness and sound velocity, i.e., the elastic properties, to the observed frequency shifts are disentangled and compared to calculated expectations. This allows to estimate the temperature dependent change of the sound velocity below the glass transition. Finally, the advantages and disadvantages of the current approach including necessary improvements are discussed.

U.5.4
16:45
Authors : Ilya V. Taydakov, Mikhail T. Metlin, Dmitry O. Goryachii, Daria A. Metlina, Nikolay P. Datskevich, Roman I. Avetisov*
Affiliations : 1 P.N. Lebedev Physical Institute of the Russian Academy of Sciences, 53 Leninsky Prospect, 119991 Moscow, Russian Federation 2Mendeleev Univeristy of Chemical Technology of Russia, 125047, Russia, Moscow, Miusskaya pl.9

Resume : A series of neodymium complexes with pyrazole-substituted 1,3-diketones, namely 1-(1,3-dimethyl-1H-pyrazol-4-yl)-4,4,4-trifluorobutane-1,3-dione, 1-(1-methy-1H-pyrazol-4-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-dione and 4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-1-(1-methyl-1H-pyrazol-4-yl) nonane-1,3-dione and 1,10-phenanthroline were successfully employed in designing of pure NIR emitting (around 1064 nm) OLEDs. Testing devises were fabricated both by thermal evaporation and solution processing (spin-coating) method. It was found that for long-chain ligands much better results can be achieved by wet deposition technique, despite sufficient thermal stability (up to 260 0C) of corresponding complexes as it was revealed by TGA/DTA analysis. The maximum EQE value of 1.38 *10-2 % was obtained for structures based on complex with the 1-(1-methy-1H-pyrazol-4-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-dione ligand. This value is close to the record results known in literature for neodymium (III) diketonate based OLEDs. Synthetic part of the work was supported by the Russian Science Foundation, project No. 19-13-00272 ?. OLEDs fabrication and testing was financially supported by the Russian Science Foundation, project No.19-79-10003

U.5.6
16:45
Authors : Rossella Yivlialin, Claudia Filoni, Alberto Calloni, Lorenzo Ferraro, Francesco Goto, Isheta Majumdar, Marco Finazzi, Lamberto Duò, Franco Ciccacci and Gianlorenzo Bussetti
Affiliations : Department of Physics, Politecnico di Milano, p.zza Leonardo da Vinci 32 - 20133 Milano (Italy)

Resume : Vacuum-deposited films of tetraphenylporphyrins (TPP) have been recently investigated for their ability in protecting the electrode surfaces from corrosion and damaging effects due to the environment [1]. The protective action of porphyrin films is strongly related to both the molecule-substrate and molecule-molecule interactions, which determine the type of film growth (e. g., layer-by-layer or layer-plus-islands) and its morphology [2]. An exemplary case is offered by meso-tetraphenyl porphyrin-Zn(II) (ZnTPP), which shows different types of molecular aggregation, depending on the substrate or on the deposition and post-growth procedures [3]. Finding the best strategy to reach a well-defined target for the film morphology plays a key role for the realization of effective protective coatings for electrodes. Within this context, we present the investigation of the morphological variation of thin ZnTPP films, as a function of the substrate temperature, ranging from -200 °C to +200 °C. ZnTPP molecules were sublimated by an organic molecular beam epitaxy (OMBE) system onto a highly oriented pyrolytic graphite (HOPG) substrate, controlled in temperature by using a variable temperature cryostat. The film morphology and type of growth were characterized ex situ by both atomic force microscopy (AFM) and reflectance anisotropy spectroscopy (RAS), the latter being highly sensitive to the orientation and type of aggregation of the ZnTPP molecules on the substrate [4]. These results will help us to select the more promising molecular coverages for the electrode surface, whose effectiveness will be checked in the future, by performing suitable corrosion tests. [1] A. Bossi, M. Penconi, R. Yivlialin, L. Duò, G. Bussetti, Exploring the role of Porphyrin Films in Graphite Electrode Protection, Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, Ed. K. Wandelt, Elsevier, 2018, 107-118. [2] M. Penconi, R. Yivlialin, G. Bussetti, L. Duò, A. Bossi, A. Orbelli Biroli, Appl. Surf. Sci. 2020, 507, 1450055; R. Yivlialin, M. Penconi, G. Bussetti, A. Orbelli Biroli, M. Finazzi, L. Duò, A. Bossi, Appl. Surf. Sci. 2018, 442, 501-506. [3] L. Raimondo, S. Trabattoni, A. Sassella, Phys. Chem. Chem. Phys. 2019, 21, 8482. [4] G. Bussetti, M. Campione, A. Sassella, L. Duò, physica status solidi (b) 2014, 252, 100-104.

U.5.10
16:45
Authors : Cristina Chircov, Alexandru Mihai Grumezescu, Alexandra Catalina Birca, Anton Ficai, Bogdan Stefan Vasile, Ecaterina Andronescu
Affiliations : Department of Science and Engineering of Oxide Materials and Nanomaterials, Faculty of Applied Chemistry and Materials Science, University Politehnica of Bucharest

Resume : In the present research study, a microfluidic platform was investigated for the successful development of carboxyl-functionalized magnetite nanoparticles. The microfluidic lab-on-chip device used for the successful synthesis and functionalization of magnetite nanoparticles was fabricated using a laser cutting machine and consisted of three poly(methyl methacrylate) plates of the same size, i.e., the top layer containing three orifices for sample injection, the bottom layer containing the cross-junction channel, and the bottom layer containing one orifice for sample collection. Each of the polymeric chips contained 20 screw orifices, and thus, were assembled using 20 M4 screws tightened at 1.5-2 Nm. The solution containing Fe(II):Fe(III) precursors at a molar ratio of 1:2 was injected through the central inlet at different flows (10, 15, 20, 25, 30, 40, and 50 rot/min), while the solution containing the precipitating agent (NH4OH 1M) and the functionalization agent (4-sulphobenzoic acid, 0, 1, 3, and 5%) was injected simultaneously through the side inlets at two different flows of 15 and 25 rot/min. In this manner, the co-precipitation of the iron ions into magnetite nanoparticles and their subsequent in situ functionalization occurred at the cross-junction of the two microchannels. The so-obtained nanoparticles were dripped from the outlet and further washed with ultrapure water and dried overnight at 40°C. The magnetite nanoparticles were subsequently characterized in terms of structure, composition, crystallinity, morphology, and functionality through X-ray diffraction coupled with Rietveld refinement, transmission electron microscopy, selected area electron diffraction, Fourier-Transform infrared spectroscopy, dynamic light scattering and zeta potential, vibrating sample magnetometry, and thermogravimetry-differential scanning calorimetry analyses. The obtained results confirmed the formation of magnetite as the unique crystalline phase, with uniform nanoparticle sizes below 10 nm and spherical shapes, and the concentration-dependent functionalization degrees. The present study further demonstrated the efficiency of the microfluidic technique for the controlled synthesis and functionalization of magnetite nanoparticles. Furthermore, it represents the initial step towards the advancement of nanoparticle-based drug delivery systems with controllable release kinetics.

U.5.11
16:45
Authors : P.V. Strekalov1, M.N. Mayakova2, M.U. Andreeva1, K.I.Runina1, D.A. Butenkov1, O.B. Petrova1, I.R. Avetisov1, I.Ch. Avetissov1
Affiliations : 1. Department of Chemistry and Technology of Crystals, D. Mendeleev University of Chemical Technology, MUCTR, Moscow, Russia 2. A.M.Prokhorov General Physics Institute RAS, GPI RAS, Moscow, Russia

Resume : Luminescent organo-inorganic hybrid materials (HM) contain nanoclusters of a highly efficient organic phosphor in a stable inorganic matrix. On the base of PbF2-containing matrices HMs were synthesized by different techniques: synthesis in low-melting glasses, solid phase recrystallization and co-precipitation using 8-hydroxyquinolate and ?-diketonate organometallic phosphors as organic constituents. In the PbF2-REF3 system (RE = rare earth element), solid solutions of the Pb1-xRExF2+x cubic phase of the fluorite Fm3m type can be formed. The high capacity of such solutions to RE, suggests the possibility of obtaining HM with high concentrations of organic components. The initial materials were lead, lanthanum, yttrium nitrates, lithium 8-hydroxyquinolate (Liq), and ammonium fluoride was used as a fluorinating agent. When obtaining HM at the first stage of the synthesis, mixing of aqueous solutions of lead nitrate and RE and a solution of 8-hydroxyquinolate lithium in ethanol was carried out. Concentrations of nitrate solutions were 1.43M and 0.8M. At the second stage of the final product was precipitated with ammonium fluoride; direct and reverse precipitation was used. As a result of co-precipitation, powders were obtained containing both the low-temperature ?-PbF2 rhombic phase and solid solutions based on ?-PbF2 cubic phase, depending on the RE concentration and synthesis conditions. It should be noted that during the deposition of nominally pure PbF2 and HM (PbF2+Liq), all powders, regardless of the conditions, corresponded to ?-PbF2. Stable single-phase powders corresponding to the ?-PbF2 structure were obtained at RE concentrations of 20-25 mol% and concentrations of nitrate solutions were 1.43M. The most intense photoluminescence (PL) was possessed by HM obtained by reverse co-precipitation with a nominal LaF3 concentration of 25 mol% and a concentration of the initial fluoride solution of 1.43M. We observed the noticeable shift of HM-PL spectra to shorter (418 nm) wavelengths relative to the initial Liq (448 nm). The short-wavelength component was obviously not associated with the centers of lanthanum or lead 8-hydroxyquinolates, which luminesced in the longer wavelength region than Liq. Also, the center cannot be due to specific bonds in PbF2 cubic phase. Since in HM, obtained by solid-phase synthesis at temperatures above 360 C, and corresponding to the crystalline PbF2 cubic phase, the maximum of the luminescence band is strongly shifted to the long-wavelength region to 511 nm. The PL intensity in this system turned out to be higher than in individual systems with lead or lanthanum fluorides, which, in combination with a very short-wavelength spectrum, seems promising. The research was financially supported by the Ministry of Science and Higher Education of the Russian Federation within the FSSM-2020-0005 project.

U.5.12
16:45
Authors : Ilya V. Taydakov1, Mikhail T. Metlin1, Dmitry O. Goryachii1, Daria A. Metlina1, Nikolay P. Datskevich1, Roman I. Avetisov2
Affiliations : 1 P.N. Lebedev Physical Institute of the Russian Academy of Sciences, 53 Leninsky Prospect, 119991 Moscow, Russian Federation 2 Mendeleev Univeristy of Chemical Technology of Russia, 125047, Russia, Moscow, Miusskaya pl.9

Resume : A series of neodymium complexes with pyrazole-substituted 1,3-diketones, namely 1-(1,3-dimethyl-1H-pyrazol-4-yl)-4,4,4-trifluorobutane-1,3-dione, 1-(1-methy-1H-pyrazol-4-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-dione and 4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-1-(1-methyl-1H-pyrazol-4-yl) nonane-1,3-dione and 1,10-phenanthroline were successfully employed in designing of pure NIR emitting (around 1064 nm) OLEDs. Testing devises were fabricated both by thermal evaporation and solution processing (spin-coating) method. It was found that for long-chain ligands much better results can be achieved by wet deposition technique, despite sufficient thermal stability (up to 260 0C) of corresponding complexes as it was revealed by TGA/DTA analysis. The maximum EQE value of 1.38 *10-2 % was obtained for structures based on complex with the 1-(1-methy-1H-pyrazol-4-yl)-4,4,5,5,6,6,6-heptafluorohexane-1,3-dione ligand. This value is close to the record results known in literature for neodymium (III) diketonate based OLEDs. Synthetic part of the work was supported by the Russian Science Foundation, project No. 19-13-00272 ?. OLEDs fabrication and testing was financially supported by the Russian Science Foundation, project No.19-79-10003

U.5.13
16:45
Authors : Despoina Tselekidou 1, Kyparisis Papadopoulos 1, Vasileios Kyriazopoulos 1,2, Konstantinos C. Andrikopoulos 3, Aikaterini K. Andreopoulou 3, Joannis K. Kallitsis 3, Argiris Laskarakis 1, Stergios Logothetidis 1, Maria Gioti 1
Affiliations : 1 Nanotechnology Lab LTFN, Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece; 2 Organic Electronic Technologies P.C. (OET), Antoni Tritsi 21B, GR-57001 Thessaloniki, Greece; 3 Department of Chemistry, University of Patras, Caratheodory 1, University Campus, GR-26504 Patras, Greece;

Resume : White Organic Light-Emitting Diodes (WOLEDs) have received broad attention for their enormous applications in the field of flat panel displays and solid-state lighting, due to their potential for low cost, solution processability, no viewing-angle dependence, and full-color capability. Obtaining white light from organic LEDs processed from wet-based techniques is a considerable challenge. Specifically, the development of new materials with improved color stability and balanced charge transport properties remains an open issue and triggers advanced research. In general, conjugated polymers composed of two complementary colors (blue and yellow or orange) or three primary colors (red, green, and blue) is a promising strategy to obtain a broad emission spectrum, and there is also the potentiality to be applied as an active layer to wet-fabricated OLED devices, which is compatible with roll-to-roll technique. In this study, novel copolymers consisting of only two chromophores are presented to induce easier emission tuning, enabling the definition of white light emission in a single polymeric layer. Carbazole derivative was utilized as the blue and host chromophore, whereas benzothiadiazole derivative was used as the red and guest chromophore in the copolymers. The selection of the chromophores was based on the combined overlaps between their emission and absorption bandwidths in order to achieve the appropriate broad emission coverage in the visible range. Thus, by carefully controlling the molar ratios of chromophores composition, the energy transfer mechanism, from blue to red chromophores, takes place. Furthermore, they exhibit excellent solubility in common solvents and processability via solution deposition techniques. We focus on the optical and photophysical properties of the monomers and copolymers, which were thoroughly investigated via NIR-Vis-far UV Spectroscopic Ellipsometry (SE), Absorbance, and Photoluminescence (PL). Following, these copolymers are used as an emissive layer and applied in solution-processed WOLED devices. The fabricated WOLED devices have been subsequently studied and characterized in terms of their electroluminescence properties and electrical characteristics. Finally, it is demonstrated that the WOLED devices possess high color stability and demonstrate CIE Coordinates (0.33, 0.38), which approach closely the pure white light CIE coordinates. Acknowledgments This research has been co?financed by the European Regional Development Fund of the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship, and Innovation, under the call RESEARCH ? CREATE ? INNOVATE (project code: T1EDK-01039).

U.5.15
16:45
Authors : Isabelle Holzer, Priscila Cavassin, Natalie Banerji
Affiliations : Christian Nielsen

Resume : In the recent years, the interest for organic bioelectronic devices increased substantially, mainly because they combine advantageous properties such as their soft and flexible nature, versatile processing and synthetic tunability. Therefore, they have a wide range of applications at the interface of biology and electronics, encompassing wearable to implantable devices, which e.g., can work as sensitive biomedical sensors. In the last decade, the research on bioelectronics was mainly focused on electrical characterization of the devices, in order to improve fabrication methods and to find better material options. Therefore, there is still a need for a more detailed knowledge on the fundamental effects occurring during the functioning of bioelectronic devices. A material which recently sparked large interest due to its high mobility of up to 1 cm2V-1s-1 in organic field effect transistors (OFET) is IDTBT, a donor-acceptor copolymer with a planar and near-torsion-free backbone allowing for such high charge carrier mobility. Four IDTBT polymers, differing in their amount of alkyl versus glycol side chains were chosen here to control the local morphology, conformation an ion-affinity of IDTBT. We used in-situ time-resolved Vis-NIR spectro-electrochemistry and where able to assign different bands in the absorption spectrum to the different kinds of species present during the doping process (neutral segments, polarons, bipolarons). Furthermore, with the help of Multivariate Curve Resolution (MCR) analysis, the evolution of the species as a function of time could be determined and an overview of the IDTBT redox kinetics was established.

U.5.16
16:45
Authors : Shubham Bhagat, Ingo Salzmann
Affiliations : Department of Physics, Concordia University, Montreal, Canada; Department of Physics, Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada;

Resume : Small conjugated molecules (CMs) and conjugated polymers (CPs) which constitute the class of organic semiconductor forms the basis of billion-dollar market for organic electronics. Unlike their inorganic counterparts, CMs and CPs offer the distinct advantage that their optical properties can be easily tuned by changes in chemical structure or chain length. Although CPs are an equally promising class of organic semiconductors, organic electronic applications are mainly based on CMs. This is to some part because CMs can be easily processed in vacuum via physical vapour deposition while CPs, being thermally fragile, are only processed by solution-based techniques. There, the extent of polymer aggregation and the growth of thin film is substantially influenced by the choice of the solvent. Moreover, solvent processing limits the temperature range available for the substrate and using atomically clean surfaces, as possible in vacuo, inaccessible. In the present work, we study the growth of CP thin films under minimum presence of solvents using Electrospray Deposition (ESD) in (ultra-)high vacuum. We elucidate the role of experimental parameters and the nature of the solvent used for ESD in order to gain control over the growth and morphology of the polymer thin film. Using ESD will enable achieving CP films on ultra-pure substrates cleaned in-vacuo and held at variable temperature, which will provide valuable information on substrate polymer interfaces. This will further allow exploring the aggregation behaviour of polymers when minimum to no solvent in present and provide the opportunity of mixing CPs and CMs for which no common solvent exists via vacuum co-deposition.

U.5.17
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Photophysics II : Sophia Hayes
09:00
Authors : F.-J. Kahle, A. Rudnick, S. Wedler, R. Saxena, R. Ammenhäuser, U. Scherf, S. Bagnich, H. Bässler, S. Athanasopoulos, A. Köhler
Affiliations : Soft Matter Optoelectronics, Universitätsstr. 30, Universität Bayreuth, 95448 Bayreuth; Soft Matter Optoelectronics, Universitätsstr. 30, Universität Bayreuth, 95448 Bayreuth; Soft Matter Optoelectronics, Universitätsstr. 30, Universität Bayreuth, 95448 Bayreuth; Soft Matter Optoelectronics, Universitätsstr. 30, Universität Bayreuth, 95448 Bayreuth; Macromolecular Chemistry Group (BUWMakro) and Wuppertal Institute for Smart Materials and Systems (CM@S), Bergische Universität Wuppertal, Gauss-Str. 20, 42119 Wuppertal; Macromolecular Chemistry Group (BUWMakro) and Wuppertal Institute for Smart Materials and Systems (CM@S), Bergische Universität Wuppertal, Gauss-Str. 20, 42119 Wuppertal; Soft Matter Optoelectronics, Universitätsstr. 30, Universität Bayreuth, 95448 Bayreuth; Bayreuth Institute of Macromolecular Research (BIMF), Universität Bayreuth, 95448 Bayreuth; Bayreuth Institute of Macromolecular Research (BIMF), Universität Bayreuth, 95448 Bayreuth; Soft Matter Optoelectronics, Bayreuth Institute of Macromolecular Research (BIMF), Bavarian Polymer Institute (BPI), Universität Bayreuth, 95448 Bayreuth

Resume : Charge transfers (CT) states play a key role in organic solar cells (OSC). In this presentation I shall demonstrate how we can use time-dependent photoluminescence measurements to identify the contributions of static and dynamic disorder in charge transfer states and their spectra. Notably, from the temperature and time dependent linewidths of absorption, fluorescence, and CT emission, we infer the static and dynamic contributions to the total disorder. We discuss the role of spectral diffusion in this process. The impact of intermolecular interactions and excited state delocalisation will also be addressed.

U.6.1
09:30
Authors : Shahidul Alam, Hua Tang, Maryam Alqurashi, Wejdan Althobaiti, Si Chen, Jafar I. Khan, Frédéric Laquai*
Affiliations : King Abdullah University of Science and Technology (KAUST), KAUST Solar Center (KSC), Physical Sciences and Engineering Division (PSE), Material Science and Engineering Program (MSE), Thuwal 23955-6900, Kingdom of Saudi Arabia

Resume : Thermally-induced degradation in bulk-heterojunction organic solar cells (OSCs) is an obvious barrier to the fabrication of stable devices. Thus, practical approaches and strategies need to be identified their inherent thermal instability. In this work, the thermally induced degradation of the most commonly used system PM6:Y6 is investigated by varying temperatures and different exposure conditions. The degradation pathways have been identified by applying several opto-electrical and spectroscopic characterizations methods. Due to the reduced charge carrier mobility and extraction probability, the thermally degraded device exhibits significant losses in the open-circuit voltage (VOC) and fill factor (FF). Furthermore, the field dependence of charge generation, charge extraction, photo-generated charge density, and charge recombination dynamics in solar cells were studied by the time-delayed collection field (TDCF) optical-pump electronic-probe technique. By using all the analyses, we can explain the significant recombination process that dominates device performance and thermal stability. Finally, device simulation by SETFOS of the current-voltage (J-V) characteristics was used to confirm experimentally determined thermally induced degradation.

U.6.2
09:45
Authors : Ishita Jalan (1), Cleber F.N. Marchiori (2), Zewdneh Genene (3), André Johansson (2), C. Moyses Araujo (2), Ergang Wang (3), Jan van Stam (1), Ellen Moons (2)
Affiliations : 1. Department of Engineering and Chemical Sciences, Karlstad University, SE-65188 Karlstad, Sweden. 2. Department of Engineering and Physics, Karlstad University, SE-65188 Karlstad, Sweden. 3. Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.

Resume : Polymeric non-fullerene acceptors offer the potential to restrict the self-aggregation that is typical for small molecule non-fullerene acceptors, which potentially yields this fine structured morphology, but phase separation is seen to be restricted. To be able to understand this, we studied a blend of the donor polymer PBDB-T and the polymeric acceptor PF5-Y5 to investigate the molecular interactions in solution in a joint experimental-theoretical spectroscopy study. Solar cells prepared of this blend have reached power conversion efficiencies of over 14% (1). From absorption spectroscopy of the PBDB-T: PF5-Y5 blend solutions at increasing temperatures, combined with concentration-dependent fluorescence spectroscopy and excitation spectroscopy, we could conclude that in addition to temperature-induced disaggregation of both donor and acceptor polymers, donor-acceptor complexes are formed in dilute blend solutions of PBDB-T and PF5-Y5. The formation of the donor-acceptor complexes competes with the donor and acceptor self-aggregation and the solvent environment is found to influence these interactions. Our results show also that the donor-acceptor polymer complexes are stabilized in more polar solvents. The near IR-region of the absorption spectrum could be matched with the calculated electronic excitations of donor-acceptor complexes of PBDB-T and PF5-Y5 oligomers. These pre-formed donor-acceptor complexes in the solution can be expected to have important consequences on the resulting film morphology. These insights are also expected to direct the future design of compatible donor-acceptor polymer pairs for high-performance all-polymer solar cells. (1) Fan, Q.; et al., Energy Environ. Sci., 2020, 13, 5017.

U.6.3
10:00
Authors : Albert Harillo-Baños, Xabier Rodríguez-Martínez, Mariano Campoy-Quiles
Affiliations : Institute of Material Science of Barcelona (ICMAB-CSIC)

Resume : Organic solar cells based on ternary active layers can lead to higher power conversion efficiencies than corresponding binaries, and improved stability. The parameter space for optimization of multicomponent systems is considerably more complex than that of binaries, due to both, a larger number of parameters (e.g., two relative compositions rather than one) and intricate morphology?property correlations. Most experimental reports to date reasonably limit themselves to a relatively narrow subset of compositions (e.g., the 1:1 donor/s:acceptor/s trajectory). This work advances a methodology that allows exploration of a large fraction of the ternary phase space employing only a few (< 10) samples. Each sample is produced by a designed sequential deposition of the constituent inks, and results in compositions gradients with ?10000 points/sample that cover about 15%?25% of the phase space, with the capability of modifying the covered zone with simple changes in deposition parameters. These effective ternary libraries are then colocally imaged by a combination of photovoltaic techniques (laser and Solar Simulator light photocurrent maps) and spectroscopic techniques (Raman, photoluminescence, absorption). The generality of the methodology is demonstrated by investigating multiple ternary systems, like PBDB-T:ITIC:PC70BM, PM6:Y6:PC70BM, and P3HT:O-IDFBR:O-IDTBR. Complex performance-structure landscapes through the ternary diagram as well as the emergence of several performance maxima are discovered.

U.6.4
10:15
Authors : Beier Hu, Jiaxin Pan, Ziming Chen, Thomas Macdonald, Artem A. Bakulin
Affiliations : Imperial College London

Resume : One of the main challenges in the development of high power-conversion efficiency halide perovskite solar cells (PSCs) is the inevitable defect formation during the material processing. This involves the shallow and deep state within the material bandgap that trigger the carrier trapping/detrapping and non-radiative recombination processes, reducing energy conversion efficiency. This makes understanding the distribution of tapping states and their effect on charge dynamics in perovskite devices fundamentally important and carrying substantial relevance for optoelectronic applications. Although significant research efforts have been dedicated to explain these physical phenomena by the commonly used tools, limitations still remain, such as, the undetectable non-emissive traps and inaccuracy due to the low signal of trapped carriers. Herein, we report the first application of the continuous-wave and impulsive pump-push-photocurrent spectroscopies to observe in real time the dynamics of carrier trapping in lead-halide perovskite solar cells. We have investigated how the external factors (e.g., temperature and electric field) impact the photovoltaic performance in PSCs via the trapped carriers. In particular, besides the further insight into realistic operating conditions, the temperature dependent measurement allows us to observe the thermally assisted trapping/detrapping and determine the trap activation energy finally. Through the systematic experimental study, we have successfully correlated the device performance with the kinetics of trapped carriers proposing new design rules for stable PSCs with high performance parameters.

U.6.5
10:30 Discussion    
10:45 Break    
 
Spectroscopy I : Martin Brinkmann
11:00
Authors : Juan Bisquert
Affiliations : Institute of Advanced Materials, Universitat Jaume I, Castelló, Spain.

Resume : The dynamic response of metal halide perovskite devices shows a variety of physical responses that need to be understood and classified for enhancing the performance and stability and for identifying new physical behaviours that may lead to developing new applications. Beyond the well-established characteristics of regular impedance arcs, we address the appearance of inductor effect at high voltage in perovskite solar cell. The impedance spectra announce the type of hysteresis, either regular for capacitive response or inverted hysteresis for inductive response. We present a physical model in terms of delayed recombination current that explains the evolution of impedance spectra and the evolution of current-voltage curves.1,2 (1) Bisquert, J.; Guerrero, A.; Gonzales, C. Theory of Hysteresis in Halide Perovskites by Integration of the Equivalent Circuit, ACS Phys. Chem Au 2021, 1, 25-44. (2) Guerrero, A.; Bisquert, J.; Garcia-Belmonte, G. Impedance spectroscopy of metal halide perovskite solar cells from the perspective of equivalent circuits, Chemical Reviews 2021, 121, 14430?14484.

U.7.1
11:30
Authors : Matteo Verdi(1,2), Jaime Segura-Ruiz(3), Andrea Ciavatti(1,2), Laura Basiricò(1,2), Annamaria Petrozza(4), Federico Boscherini(1) and Beatrice Fraboni(1,2)
Affiliations : (1) Department of Physics and Astronomy, University of Bologna, Bologna, Italy. (2) National Institute for Nuclear Physics INFN, Bologna, Italy. (3) ID16B ? ESRF: The European Synchrotron, 71 avenue des Martyrs, 38043 Grenoble, France. (4) Center for Nano Science and Technology PoliMi, Istituto Italiano di Tecnologia, 20133 Milano, Italy.

Resume : Large-area, low?cost and highly sensitive high energy radiation detectors are of great interest in the fields of medical diagnostics, dosimetry, industrial inspection, and security. State?of?the?art solid-state X? and gamma?ray detectors for large-area applications based on silicon (Si), amorphous selenium (a?Se), and cadmium zinc telluride (CdZnTe) are difficult to scale up, and have high operating voltage [1]. Recently, lead?halide perovskites emerged as an auspicious novel materials family for X? and gamma?ray detection thanks to strong absorption of ionizing radiation, high charge carrier mobilities, long exciton diffusion, long charge carrier lifetime, and excellent optical properties [2]. Perovskite can be deposited by solution at low temperature constituting a great alternative for the production of large-area low-cost sensors. X-ray Nanoanalysis uses focalized synchrotron radiation combined with techniques like X-ray fluorescence (XRF) and X-ray induced current (XBIC) to probe materials and devices at the nanoscale. Using a precise positioning system is possible to scan an area of interest obtaining a map with nanometer resolution. The ID16B beamline at the ESRF provides a nanobeam spot size on the sample down to 50nm x 50nm. The detectors and instrumentations available in the end station enable the user to perform several experimental techniques at the same time [3]. We used the nanofocused beam of the ID16B beamline at the ESRF to acquire simultaneously XRF and XBIC signals from novel perovskite thin-film X-ray detectors in order to study the relation between composition and electric transport at the nanoscale. In perovskite solar cells Phenyl-C61-butyric acid methyl ester (PCBM) is often used as electron transport layer and its good performance is associated with trap passivation [4]. Here we used 2-fold X-ray nanoanalysis to visualize the effect of PCBM on methylammonium lead iodide (MAPbI3) perovskite nanocrystals. The same Perovskite/PCBM blend is used for X-ray detection. The polymer permeates the nanocrystal layer passivating the surface traps enhancing the detection performances reaching a sensitivity as high as 2270 µC Gy?1 cm?2 under 40kV X-ray, at 4V bias [5]. The combination of the elemental distribution and XBIC signal allows to understand how PCBM passivates charge traps located at the grain boundaries improving the performances of the perovskite layer for ionizing radiation detection. In samples with only MAPI3 nanocrystals, we observed higher photocurrent along the grain boundaries than in the middle of the grains. The passivation of defects by PCBM increases the charge collection from the middle of the grain. The comparison of the XRF and XBIC signals shows a higher correlation between fluorescence intensity and current signal in the case of MAPbI3/PCBM blend than perovskite only devices.

U.7.2
11:45
Authors : Jiaxin Pan, Ziming Chen, Tiankai Zhang, Feng Gao, Artem Bakulin
Affiliations : Imperial College London

Resume : In perovskite solar cells (PSCs), trap states are considered one of the main factors limiting the device performance (e.g., open-circuit voltage and short-circuit current) as they reduce the mobility of photogenerated carriers and cause trap-assisted recombination [1]. In such a case, trap passivation becomes a popular method to boost device performance, and reports show that passivating surface traps of perovskite become more effective than passivating their bulk traps. Material scientists attribute the better effect of surface passivation to the significant reduction of trap density in perovskites since the majority amount of traps state are considered located at the perovskite surface. We report a pump-push photocurrent spectroscopy study, which is able to trace the dynamics of trapped carriers using a delayed infrared push pulse to bring carriers from defect states to the conduction band. We found that the trapping time as well as recombination time for trapped states are dominant factors towards the device performance of PSCs[2]. Via investigating the lifetime of FAPI solar cells with and without surface passivation, we observed that carriers in surface traps recombine much faster than that in bulk traps, illustrating that surface defects have a much higher possibility to re-trap carriers generated under continuous light illumination. With such a clearer understanding of the trapped carrier dynamics, we anticipate our assay to be another starting point for material scientists to further improve existing PSC performance. [1] F. Gao, Y. Zhao, X. Zhang and J. You, Advanced Energy Materials, 2019, 10, 1902650. [2] A. Bakulin, A. Rao, V. Pavelyev, P. van Loosdrecht, M. Pshenichnikov, D. Niedzialek, J. Cornil, D. Beljonne and R. Friend, Science, 2012, 335, 1340-1344.

U.7.3
12:00 Discussion    
12:15 Lunch Break    
13:45 Plenary session 1 + break    
 
Structure and Properties I : Ingo Salzmann
15:00
Authors : Sebastian Hofer, Andreas Hofer, Johanna Unterkofler, Wolfgang Bodlos, Adrián Tamayo, Tommaso Salzillo, Marta Mas-Torrent, Michael Ramsey, Jiri Novak, Alessandro Sanzone, Luca Beverina, Yves Henry Geerts, Roland Resel
Affiliations : Institute of Solid State Physics, Graz University of Technology, Austria; Institut de Ciència de Materials, Universitat Autònoma de Barcelona, Spain; Institute of Physics, Karl-Franzens University Graz, 8010 Graz, Austria; Department of Materials Science, University of Milano-Bicocca, Italy; Department of Condensed Matter Physics, Masaryk University, Brno, Czech Republic; Laboratoire de Chimie des Polymères, Universite? Libre de Bruxelles, Belgium;

Resume : The class of benzothieno-benzothiophene (BTBT) type molecules are among the best performing active organic semiconductors in organic thin film transistors. Functionalization of this molecule by a phenyl group on one terminal end and a decyl group at the other end results in an asymmetric molecule (Ph-BTBT-10). This asymmetry induces specific thin film forming properties and unique crystallographic features substantially different from organic semiconducting molecules which have symmetrical shape. The first outstanding observation is related to the thin film formation starting from the first monolayer up to device relevant thin films. The equilibrium bulk structure is formed just within the first monolayer and a metastable phase is found at later growth stages. This sequence is reversed to frequently observed substrate-induced polymorphism. An explanation is based on kinetically driven cross-nucleation. [1] The second interesting observation is related to crystallographic defects within thin films. Crystallisation far from equilibrium, e.g. by crystallization from melt or gradient crystallization, causes systematic broadening of X-ray diffraction peaks. The sequence of peak broadening can be explained only in case of introducing crystal defects caused by inverted molecules incorporated into the crystal structure. [2] Healing of the defects is obtained by annealing of the films towards a phase transition into a liquid crystalline state. This process is observed irreversible. We report also on the utilization of the smectic E phase for obtaining highly ordered crystallographically thin films for transistor application. [3] Finally, device performance is reported on uniaxially oriented crystals prepared by blade coating. [4] [1] S. Hofer et al., J. Mater. Chem. C 125, 28039-28047 (2021). [2] S. Hofer, et al., Chem. Mater. 33, 1455?1461 (2021). [3] S. Hofer, et al., Liquid Crystals 48(13), 1888-1896 (2021). [4] A. Tamayo, et al., J. Mater. Chem. C 9(22), 7186 ? 7193 (2021).

U.8.1
15:15
Authors : Peter Müller-Buschbaum
Affiliations : Lehrstuhl fu?r Funktionelle Materialien, Physik-Department, Technische Universita?t Mu?nchen, James-Franck-Str. 1, 85748 Garching, Germany

Resume : Based on novel conjugated semiconducting polymers, organic solar cells are an interesting alternative to conventional silicon based solar cells as they feature new possibilities in fabrication and utilization. Using wet chemical processing, they can be manufactured with large-scale production methods such as roll-to-roll printing. They are light-weight and flexible, which offers novel ways for building integration of use in off-grid applications. However, in terms of large-scale usability, one of the major challenges for polymer-based organic solar cells is to overcome their relatively short lifetime, as compared to their inorganic counterparts. To gain a deeper understanding of organic solar cell degradation with respect to changes in the active layer morphology, we present operando studies during the first hours of operation. The studies reveal information on both, its evolving current-voltage characteristics and the changes of the active layer morphology in the organic solar cells. For that purpose, advanced x-ray scattering methods (GISAXS / GIWAXS measurements) and current-voltage (IV) tracking of the operating solar cell are performed simultaneously to gain fundamental understanding. Starting from an optimized morphology of the active layers in terms of highest device efficiencies, depending on the donor-acceptor system, different morphological degradation pathways are identified. Either a mixing or a demixing process can occur during degradation and cause changes of the active layer morphology. The altered morphology is less optimal for charge transport through the active layer due to poor percolation in a too fine morphology or a poor splitting of excitons in a too coarse morphology. Different examples for both degradation pathways will be discussed. Moreover, the impact of additives on device performance, stability and degradation pathway will be investigated. References [1] Schaffer, C. J.; Palumbiny, C. M.; Niedermeier, M. A.; Jendrzejewski, C.; Santoro, G.; Roth, S. V.; Müller-Buschbaum, P. A Direct Evidence of Morphological Degradation on a Nanometer Scale in Polymer Solar Cells. Adv. Mater. 2013, 25, 6760? 6764. [2] Wang, W.; Schaffer, C. J.; Song, L.; Körstgens, V.; Pröller, S.; Indari, E. D.; Wang, T.; Abdelsamie, A.; Bernstorff, S.; Müller-Buschbaum, P. In Operando Morphology Investigation of Inverted Bulk Heterojunction Organic Solar Cells by GISAXS. J. Mater. Chem. A 2015, 3, 8324? 8331. [3] Yang, D.; Löhrer, F. C.; Körstgens, V.; Schreiber, A.; Bernstorff, S.; Buriak, J. M.; Müller-Buschbaum, P. In-Operando Study of the Effects of Solvent Additives on the Stability of Organic Solar Cells Based on PTB7-Th:PC71BM. ACS Energy Lett. 2019, 4, 464? 470. [4] Yang, D.; Löhrer, F. C.; Körstgens, V.; Schreiber, A.; Cao, B.; Bernstorff, S.; Müller-Buschbaum, P. In Operando GISAXS and GIWAXS Stability Study of Organic Solar Cells Based on PffBT4T-2OD:PC71BM with and without Solvent Additive. Adv. Sci. 2020, 7, 2001117. [5] Wienhold, K. S.; Chen, W.; Yin, S.; Guo, R.; Schwartzkopf, M.; Roth, S. V.; Müller-Buschbaum, P. Following in Operando the Structure Evolution-Induced Degradation in Printed Organic Solar Cells with Nonfullerene Small Molecule Acceptor. Sol. RRL 2020, 4, 2000251.

U.8.2
15:30
Authors : J. Rozbo?il, K. Broch, R. Resel, O. Caha, F. Münz, P. Mikulík, J.E. Anthony, H. Sirringhaus, and J. Novák
Affiliations : J. Rozbo?il; O. Caha; F. Münz; P. Mikulík; J. Novák - Department of Condensed Matter Physics, Masaryk University, Kotlá?ska 2, 61137 Brno, Czech Republic; K. Broch - Institute for Applied Physics, Eberhard-Karls Universität Tübingen, Auf der Morgenstelle 10, Germany; R. Resel - Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria; J.E. Anthony - Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506, USA; H. Sirringhaus - Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK

Resume : We have employed x-ray grazing incidence diffraction (GIXD), x-ray specular reflectivity, and Vis reflection spectroscopy to follow phase transitions in spin-coated thin films of the high mobility organic semiconductor 5,11-Bis(triethyl silylethynyl) anthradithiophene (TES-ADT). The phase behavior of the films is studied both during aging in an ambient atmosphere and during thermal annealing. The as-deposited amorphous films progressively transform towards monoclinic and triclinic alpha phases on the time-scale of several days. Furthermore, using GIXD, we determine the temperature dependence of lattice parameters of the alpha phase and the structure of the high-temperature beta phase. Surprisingly we find that the transformation from the alpha to the beta phase takes place only for films thicker than approximately 70 nm at 130 degC. Instead, for layers thinner than this critical thickness the films become amorphous above the same transition temperature. We attribute the observed thickness hindered phase behavior to the interplay between the surface and the bulk energies of the competing phases. Additionally, the combination of x-ray scattering techniques and Vis spectroscopy allows us to show the two-step nucleation character of the alpha to the beta phase transition. Here, the beta phase nucleates from the intermediate amorphous phase.

U.8.3
15:45
Authors : Roth, S. V.*(1,2), Brett, C. J. (1,2), Månsson, M.(2), Frielinghaus, H.(3), Porcard, L.(4), Müller-Buschbaum, P.(5,6), Söderberg, L.D.(2)
Affiliations : (1)Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany; (2)KTH Royal Institute of Technolo-gy, Stockholm, Sweden; (3)Jülich Centre for Neutron Science JCNS, Garching, Germany; (4)Institut Laue-Langevin ILL, Grenoble, France; (5)Lehrstuhl für Funktionelle Materialien, Physik-Department, TU München, Garching, Germany; (6)Heinz-Maier-Leibniz-Zentrum MLZ, TU München, Garching, Germany

Resume : Conjugated polymer blend, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), play a vital role as blocking layers and electrodes in organic solar cells. Especially in combination with structural biomaterials, such as cellulose nanofibrils (CNF), novel applications in flexible devices become possible. Here, spray deposition, as a facile and scalable layer-by-layer (LbL) coating technique, has been successfully applied to fabricate tailored CNF films [1]. Their nanoscale structure and response to external stimuli as well as long-term stability is crucial for their application. Hence, we use a combination of grazing incidence neutron and x-ray scattering to elucidate the molecular and nanoscale structure of these novel hybrid materials and to correlate this with their optoelectronic functionality. To start with, we investigated the nanostructure of CNF films of varying thickness, observing a morphological gradient in length scales throughout the film thickness [1]. With neutrons being highly sensitive to water content and CNF being hygroscopic, we successfully investigated the response of different charged, ultrasmooth CNF films to cyclic humidity changes [1]. This allows for uniquely characterizing the nanoscale, hierarchical, nanoporous structure of these films. In a next step, we filled the existing voids with a semiconducting conjugated polymer blend, used in organic electronics and [2]; we characterized their performance under cyclic stability conditions of this novel conjugated-polymer-CNF-based electrode concerning conductivity under humidity changes. The resulting electronic changes were directly correlated to the reversible nanostructure changes. As a step toward tunable plasmonic sensors and plasmonic electrodes, we investigated the thermally induced band-gap tuning of silver-nanoparticle-CNF hybrids; here, the CNF template guides the synthesis the silver nanoparticles at the CNF interface [3]. [1] Brett, C. J. et al., Macromolecules 52, 4721?4728 (2019). [2] Brett, C. J. et al., ACS Appl. Mater. Interfaces 13, 27696?27704 (2021). [3] Brett, C. J., Adv. Electron. Mater. 7, 2100137 (2021).

U.8.4
16:00
Authors : Ann Maria James*?, Lara Gigli+, Nicola Demitri+,Yves H. Geerts?, Roland Resel?
Affiliations : ? Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz,Austria ? De?partement de Physique, Faculte?des Sciences, Universite?Libre de Bruxelles CP223, Campus de la Plaine, 1050 Brussels, Belgium +Elettra-Sincrotrone Trieste, S.S. 14 Km 163.5 in Area Science Park, 34149 Basovizza-Trieste, Italy

Resume : Organic semiconductors (OSCs) are promising for thin-film transistor applications as they potentially offer distinctive advantages over their inorganic counterparts, particularly in terms of their properties, processing techniques and cost-effectiveness. Small molecules with extended aromatic core and solubilizing long chains are budding candidates for solution-processed organic semiconductors. However, as small molecular OSCs are held together by weak non-directional van der Waals force, they tend to exhibit many alternative packing arrangements with differences in structure and energy leading to polymorphism. The utilisation of solid surfaces (substrates) as a nucleation or crystallisation mediator was a strategy used to identify new thin-film phases. We could successfully demonstrate that defined innovations in the experimental protocol (like the choice of solvent, temperature etc.) can promote tuning between polymorphs as different local energy minima become accessible. Among the various OSCs, small molecules with[1]benzothieno [3,2-b]benzo thiophene (BTBT) cores are identified as the best p-type semiconductor. Here we investigated the crystal structure solution, film-forming and charge transport properties of FD44 (OEG BTBT), a BTBT derivative. Also, extensive investigations carried out by altering the experimental protocols employed in the fabrication of thin films at the vicinity of a substrate revealed four new thin-film phases. Specular and grazing incidence X-ray diffractions were performed using in-house X-ray equipment and synchrotron to determine the crystallographic structure within the thin films. Furthermore, our detailed investigations helped us in understanding the origin and stability of these new polymorphic forms and thereby gain control over the conditions that led to their formations. Controlling the polymorphism of OSCs within thin films is crucial because they form the active channel layer in most organic electronic devices, and dramatic variations in charge transport can be induced even by small changes in the molecular packing.

U.8.5
16:15 Discussion    
16:30 Break    
 
Structure and Properties II : Emanuele Orgiu
16:45
Authors : Leticia Christopholi [1], Ishita Jalan [2], Zafer Hawash [1], Leif Ericsson[1], Jan van Stam[2], Ellen Moons [1]
Affiliations : 1. Department of Engineering and Physics, Karlstad University, SE-65188 Karlstad, Sweden. 2. Department of Engineering and Chemical Sciences, Karlstad University, SE-65188 Karlstad, Sweden.

Resume : The film morphology in the active layer of non-fullerene acceptor organic solar cells is key to their high performance. Numerous studies of nanostructured donor-acceptor blend films by scanning probe microscopy techniques have resulted in surface topography images without resolving the actual distribution of donor and acceptor molecules. Scanning X-ray Transmission Microscopy (STXM) has been a valuable synchrotron-based technique that made it possible to image the composition of donor-acceptor blend films with resolutions below 50 nm. STXM imaging was particularly successful for polymer-fullerene blends, thanks to the distinct X-ray absorption resonance of the fullerene cage. Unlike fullerenes, the non-fullerene acceptors are more difficult to chemically distinguish from the donor polymers in the bulk heterojunction films. The AFM-IR technique combines the high resolution of scanning probe microscopy with the chemical fingerprint of infrared spectroscopy. I will demonstrate for some examples from organic photovoltaics that compositional variations in the non fullerene acceptor blend films can be mapped in great detail and with low beam damage. I will furthermore show examples where AFM-IR could reveal changes in metal halide perovskite films upon degradation in air. The results demonstrate the potential of AFM-IR as a high-resolution and non-destructive chemical analysis technique for emerging photovoltaic materials.

U.9.1
17:15
Authors : M. F. Schumacher (1), T. G. Nguyen (1), J. Zablocki (1), A. Lützen (1), N. J. Hestand (2), F. Balzer (3), K. Hingerl (4), M. Schiek (4).
Affiliations : (1) University of Bonn, Germany; (2) Evangel University, Springfield Missouri, USA; (3) University of Southern Denmark, Sonderborg, Denmark; (4) Johannes Kepler University Linz, Austria.

Resume : Semiconducting organic molecules are revolutionizing the electronics world by providing new and easily adjustable materials for various opto-electronic and bio-electronic applications [1]. Benefiting from recent developments, neurostimulating prosthetics to restore light sensitivity of degenerated retina will eventually be conceivable. The functionality of this concept has already been demonstrated using a small molecular squaraine dye (SQIB) as active material [2]. For such optoelectronic sensing, however, it is essential to acquire a fundamental understanding of the underlying processes and mechanisms such as the generation and nature of the molecular excitons [2, 3]. N-alkyl anilino squaraines have been shown to exhibit strong excitonic intermolecular interactions, without the SQIB-typical formation of a self-assembled crystalline micro- or nanotextured morphology [3, 4]. Molecular aggregates with short intermolecular distances combine short-range intermolecular charge transfer (ICT) interactions with Frenkel excitons providing a striking feature of these n-alkylated anilino squaraine dyes [4, 5]. Here, we investigate the structure-correlated excitonic properties in photoactive thin-film semiconductors for bio-optoelectronics using known non-chiral (nBSQ, nOSQ) and two new structurally related chiral anilino squaraines (nOCi-SQ, nCi-SQIB). Functionalisation with enantiomerically pure citronellyl-derived residues ensures the analogy to the corresponding n-alkylated compounds and additionally offers the investigation by Mueller matrix polarimetry [6] due to an emerging excitonic chiral dichroism (CD) [7]. This allows a systematic and fundamental study of the structure and chirality correlated excitonic properties approaching a quantitative understanding of excitation pathways. [1] Irimia-Vladu, Glowacki, Sariciftci, Bauer (editors): Green Materials for Electronics, Wiley-VCH, ISBN 9783527692958 (2017). [2] Abdullaeva, Balzer, Schulz, Parisi, Lützen, Dedek, Schiek. Adv. Funct. Mater. 29 (2019) 1805177. [3] Balzer, Abdullaeva, Maderitsch, Schulz, Lützen, Schiek. Phys. Status Solidi B 257 (2020) 1900570. [4] Zablocki, Schulz, Schnakenburg, Beverina, Warzanowski, Revelli, Grüninger, Balzer, Meerholz, Lützen, Schiek. J. Phys. Chem. C 124 (2020) 22721?22732. [5] Hestand, Zheng, Penmetcha, Cona, Cody, Spano, Collison. J. Phys. Chem. C 119 (2015) 18964?18974. [6] Arteaga, Ossikovsky. J. Opt. Soc. Am. A 36 (2019) 416-427. [7] Balzer, Schumacher, Matiello, Schulz, Zablocki, Schmidtmann, Meerholz, Sariciftci, Beverina, Lützen, Schiek. Isr. J. Chem. doi: 10.1002/ijch.202100079.

U.9.3
17:30
Authors : Alberto Salleo
Affiliations : Stanford University, Dept. of Materials Science and Engineering

Resume : Organic semiconductors are an interesting materials family for number of technologies including solar cells, LEDs, transistors and sensors. The fundamental premise of organic semiconductors is that synthetic chemists can generate materials with properties “on demand”. Unfortunately, even if this became a reality, we would not know what to order! Indeed, while organic semiconductors have been around for a while, the preeminent role of the microstructure in governing their properties is far from understood. In this seminar, I will emphasize the role played by structure at different length-scales and how charge transport is a complex multi-scale phenomenon. We use charge-modulated IR spectroscopy to measure the delocalization of charges in crystallites. Correlating carrier mobility to charge delocalization highlights the importance of mesoscale film properties, such as the connectivity of aggregates by tie-chains. As a result, we study the mesoscale organization of polymers using new techniques in the transmission electron microscope and complementary X-ray diffraction measurements at the synchrotron. By combining these techniques we are able to study the microstructure across a range of length-scales in real space and reciprocal space. Microstructural analysis at these lengthscales coupled with charge transport theory allows to better understand the role of defects. Thus, such multiscale stu

U.9.4
18:00 Discussion    
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Thermoelectrics : Giovanni Costantini
09:00
Authors : Dr Oliver Fenwick
Affiliations : School of Engineering and Materials Science, Queen Mary University of London, UK.

Resume : Obtaining accurate thermal conductivity measurements is challenging for any material, but particularly where the amount of material is small or its thermal conductivity is low. Thermal conductivity measurements are therefore not straightforward for thin films of organic and hybrid thermoelectric materials. In this presentation I will present our work on pseudo-steady state 3-? measurements of thermal (and thermoelectric) properties of doped polymer [1] and halide perovskite films [2-4]. I will demonstrate the ability of the technique to detect changes in thermal conductivity due to doping-induced morphology changes in polymers [1], electronic contributions to thermal conductivity [3] and phase changes [4]. I will also show how the technique can be applied to thin films with anisotropic in-plane thermal conductivity [1]. Many models of thin film thermal conductivity measurement neglect the effect of nanoscale topography on the measurement. I will present computational and experimental data quantifying the effect of topography on extracted values of thermal conductivity, and will identify regimes where we can have confidence in our results and regimes where we would need to apply correction factors. [1] High thermal conductivity states and enhanced figure of merit in aligned polymer thermoelectric materials. T. Degousée et al., J. Mater. Chem. A, 9 (29), 16065-16075, 2021. [2] Substitutional doping of hybrid organic-inorganic perovskite crystals for thermoelectrics. W. Tang et al., J. Mater. Chem. A, 8 (27), 13594-13599, 2020. [3] Enhanced control of self-doping in halide perovskites for improved thermoelectric performance. T. Liu et al., Nat. Commun., 10 (1), 5750, 2019. [4] Unusual Thermal Boundary Resistance in Halide Perovskites: A Way To Tune Ultralow Thermal Conductivity for Thermoelectrics. T. Liu et al. ACS Appl. Mater. & Interfaces, 11 (50), 47507-47515, 2019.

U.10.1
09:30
Authors : Osnat Zapata-Arteaga.1, Sara Marina2, Guangzheng Zuo.3, Kai Xu.1, Bernhard Dörling1, Luis Alberto Pérez1, Juan Sebastián Reparaz1, Jaime Martín2,4,5, Martijn Kemerink6,7, and Mariano Campoy-Quiles1,?
Affiliations : 1 Institute of Materials Science of Barcelona (ICMAB-CSIC). Campus UAB08193 Bellaterra, Spain; 2 POLYMAT and University of the Basque Country. Av Tolosa 72, 2018, Spain; 3 Institute for Physics and Astronomy, University of Potsdam. 14476 Potsdam-Golm, Germany; 4 Grupo de Polímeros, Centro de Investigacións Tecnolóxicas (CIT). Universidade da Coruña, Esteiro, 15471 Ferrol, Spain; 5 Ikerbasque, Basque Foundation for Science. 48013 Bilbao, Spain; 6 Centre for Advanced Materials, Heidelberg University. Im Neuenheimer Feld 225, 69120 Heidelberg, Germany.; 7 Division of Electronics and Photonic Materials, Department of Physics, Chemistry and Biology. Linköping University, Linköping, Sweden.

Resume : The thermoelectric properties of polymer semiconductors vary significantly with the structural order and carrier concentration. Within this context, mixing a given polymer semiconductor with a guest material is of significant interest as it opens new pathways to fine-tune the structural order, morphology, and even the energy landscape. In this work, we present a combinatorial study of the thermoelectric properties of mixtures of various guest materials with the host workhorse polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). By varying the composition and employing thickness gradients, we effectively characterize nearly 200 samples thanks to locally resolved measurements. We find that mixtures of PBTTT with 10 wt% - 15 wt% of poly(3-hexylthiophene-2,5-diyl) (P3HT) as the guest material have up to a 5-fold higher power factor compared to pure PBTTT, leading to zT values around 0.1. Then, through spectroscopic analysis of the charge-transfer species, structural characterization using GIWAXS and AFM, and Monte Carlo simulations, we find that our results are due to P3HT promoting long-range electrical connectivity and low disorder while both materials also share similar HOMO levels, ensuring electronic connectivity.

U.10.2
09:45
Authors : Anna Lena Oechsle (1), Julian E. Heger (1), Nian Li (1), Shanshan Yin (1), Sigrid Bernstorff (2) & Peter Müller-Buschbaum (1,3)
Affiliations : (1) Technische Universität München, Physik-Department, Lehrstuhl für Funktionelle Materialien, James-Franck-Str. 1, Garching, Germany (2) Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 km 163.5, AREA Science Park, Basovizza 34149, Italy (3) Heinz Maier-Leibnitz Zentrum (MLZ), Lichtenbergstr. 1, 85748 Garching, Germany

Resume : Thermoelectric (TE) generators are considered a promising technique for heat waste recovery as they enable a direct conversion of a temperature gradient into electrical power. Especially polymer based organic thermoelectric materials are very advantageous, offering a wide range of applications as these materials allow a large scale, low-cost solution based processability of low or non-toxic, lightweight, and flexible TE devices. The blend poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is a p-type semiconductor, which gained high interest as TE material. In recent years, research was focusing on the further improvement of TE properties of PEDOT:PSS with different treatment approaches like addition of surfactants, high-boiling-point solvents, acids and bases or inorganic salts. Very promising is the post-treatment of PEDOT:PSS thin films with ionic liquids (ILs), as two important TE parameters, Seebeck coefficient (S) and electric conductivity (?), can be increased simultaneously. To understand the respective underlying effects, we post-treated PEDOT:PSS thin films with three different ILs in varying concentrations and investigated the film properties with diverse techniques. With UV-Vis spectroscopy, we were able to directly correlate the increase in S with a change in the doping level of the PEDOT chains. While the increase in ? is mainly caused by a morphological rearrangement towards an optimized PEDOT domain distribution, which we demonstrated by performing grazing incidence small angle X-ray scattering (GISAXS) and conductive atomic force microscopy (c-AFM) [1]. However, to make these PEDOT:PSS thin films usable in future commercial TE devices it is indispensable to also investigate the performance of these materials for their long-term stability under different ambient conditions, like elevated temperature or increased humidity. Therefore, we performed in-situ GISAXS measurements using a custom-built chamber in which we can heat the ILs post-treated thin films to different temperatures or expose them to a certain humidity, while simultaneously measuring the thin film conductivity. With these in-situ GISAXS investigations and combined with additional measurement techniques like for example in-situ UV-Vis, we are able to investigate the morphology and doping level evolution during operation of thermoelectric PEDOT:PSS thin films under different ambient conditions [2]. These studies give an important insight and understanding of the impact that the operation environment will have for future PEDOT:PSS based TE devices in terms of long term stability. References [1] A. L. Oechsle, J. E. Heger, N. Li, S. Yin, S. Bernstorff, P. Müller-Buschbaum, Macromol. Rapid Commun. 2021, 42, 2100397. [2] A. L. Oechsle, J. E. Heger, N. Li, S. Yin, S. Bernstorff, P. Müller-Buschbaum, to be published

U.10.3
10:00 Discussion U.9 & U.10    
10:15 Break    
 
Advanced Devices : Oliver Fenwick
11:00
Authors : Andrea Ciavatti(1,2), Ferdinand Lédée (1), Matteo Verdi (1,2), Laura Basiricò (1,2), and Beatrice Fraboni (1,2)
Affiliations : 1- Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy 2 - National Institute for Nuclear Physics ? INFN section of Bologna, Viale Berti-Pichat 6/2, Bologna 40127, Italy

Resume : 2D layered hybrid perovskites have recently attracted an increasing interest as active layers in LEDs and UV-Vis photodetectors. 2D perovskites crystallize in a natural self-assembled quantum well-like structure and possess several interesting features among which low-temperature (< 100 °C) synthesis and low defect density. We present in this work solid-state ionizing radiation direct detectors based on the 2D layered hybrid perovskite PEA2PbBr4 (PEA = C6H5C2H4NH3+) deposited from solution using scalable techniques and directly integrated onto a pre-patterned flexible substrate in the form of micro-crystalline films displaying crystal-like behaviour, as evidenced by the ultra-fast (sub-microsecond) and good detection performances under UV light. The effective detection of X-Rays (up to 150 kVp) is demonstrated with Sensitivity values up to 806 ?C Gy-1 cm-2 and a Limit of Detection (LoD) of 42 ± 4 nGy s-1, thus combining the excellent performance for two of the most relevant figures of merit for solid-state detectors. Additionally, the tested devices exhibit exceptionally stable response under constant irradiation and bias, assessing the material robustness and the intimate electrical contact with the bottom electrodes. PEA2PbBr4 micro-crystalline films directly grown on flexible pre-patterned substrate open the way for large-area solid-state detectors working at low radiation flux for ultra-fast X-Ray imaging and dosimetry.

U.11.1
11:30
Authors : Alina Irina RADU (1,2), Vlad-Andrei ANTOHE (2,3), Sorina IFTIMIE (2), Iulia ANTOHE (1), Mihaela FILIPESCU (1), Adrian RADU (2), Diana COMAN (2), Maria Luiza STINGESCU (2), Elena-Isabela BANCU (1), Maria DINESCU (1), Stefan ANTOHE (2,4,*)
Affiliations : (1) National Institute for Lasers, Plasma and Radiation Physics (INFLPR), Atomistilor Street 409, 077125 Magurele, Ilfov, Romania; (2) University of Bucharest, Faculty of Physics, R&D Center for Materials and Electronic & Optoelectronic Devices (MDEO), Atomistilor Street 405, 077125 Magurele, Ilfov, Romania; (3) Université catholique de Louvain (UCLouvain), Institute of Condensed Matter and Nanosciences (IMCN), Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; (4) Academy of Romanian Scientists (AOSR), Splaiul Independentei 54, 050094 Bucharest, Romania; *Corresponding author: santohe@fizica.unibuc.ro (S. ANTOHE); Contact author: vlad.antohe@fizica.unibuc.ro (V. A. ANTOHE).

Resume : The properties of a novel P3HT:PC71BM:SnO2-nanoparticles (NPs) composite, used as potential absorber for Organic Photovoltaic Cells (OPCs), were investigated. The structural, morphological and optical characterizations of this composite demonstrated an enhancement of the ITO/PEDOT:PSS/P3HT:PC71BM:SnO2-NPs/LiF/Al ternary structure when compared to the ITO/PEDOT:PSS/P3HT:PC71BM/LiF/Al binary one. This behavior is due, on one hand to the fact that SnO2-NPs behave as a secondary non-fullerene acceptor, and on the other hand to the superior electrical conductivity of the SnO2-NPs, very well dispersed in the polymeric blend as compared to other nanostructured inorganic materials. These properties led to a better photogeneration and transport of charge carriers, decreasing the series resistance, increasing the fill factor, and consequently the cell?s efficiency, too. The incorporation of nanoparticles into ternary OPCs could represent a way to enhance their performances by improving the photogeneration of charge carriers, as well as their transport and collection to the electrodes. Keywords: Conductive polymers; Fullerene derivatives; Tin dioxide nanoparticles (SnO2-NPs); Organic photovoltaic cells (OPCs). Acknowledgements: This research was supported by the "Executive Unit for Financing Higher Education, Research, Development and Innovation" ? UEFISCDI (Romania) through the grants: 115/2020 (PN-III-P1-1.1-TE-2019-0868), 25/2020 (PN-III-P1-1.1-TE-2019-0846), 195/2020 (PN-III-P1-1.1-PD-2019-0466), and 40PCCDI/2018.

U.11.2
11:45
Authors : Stoeckel, M.-A.*(1), Wu, H.-Y.(1), Lu, Y.(2), Yang, C.-Y.(1), Wu, Z.(3), Woo, H.Y.(3), Pei, J.(2), Berggren, M.(1), Fabiano, S.(1)
Affiliations : (1) Laboratory of Organic Electronics, Department of Science and Technology, Linköping University, Norrköping, Sweden (2) Beijing National Laboratory for Molecular Sciences (BNLMS), Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center of Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871 China (3) Department of Chemistry, College of Science, Korea University, Seoul, 136-713, Republic of Korea

Resume : High-performing organic materials are required for efficient opto-, bioelectronic and thermoelectric applications. Among these materials, (semi-)conducting polymers are particularly appealing for these technologies, as they benefit from unique optoelectronic properties, low-cost production and their solution processability make them fully compatible with large-scale deposition methods. The most common way to reach high electrical conductivities with this class of materials is to dope the polymers through the addition of a heterogeneous doping entities to the system. With the goal to produce highly-performing materials, huge efforts have been provided by the scientific community, notably through molecular design adjustments of these active materials. A current strategy towards this end is the planification and the rigidification of the polymer backbone, leading to a higher degree of order through a favorable molecular packing while decreasing the energetic disorder. This is the case, for example, for poly(p-phenylene vinylene) derivatives that benefit from both carbon-carbon double bonds between polymer units and intramolecular hydrogen bonds. Another way of enhancing the performances of (semi)conducting polymers is to increase the microscopic order and then the crystallinity of the polymeric assembly by adjusting the processing of deposition. One way to do so is to use Langmuir-Schaefer (LS) technique that relies on the assembly of the polymer chains at the air/water interface when compressed between two moving barriers. The assembled film composed by a monolayer of polymers with a low degree of defect is then transferred onto a substrate integrating electrodes to make a fully functional device. Here we report on LS films that are highly ordered and oriented at the monolayer limit. This describes a microscopic structure that is optimized for the transport of charges with strong anisotropic properties of electron conduction. Through a systematic analysis including scanning probe microscopy, optical spectroscopy, GIWAXS, NEXAFS and electrical measurements, we characterized the system in terms of structure, packing, energetics, and thermoelectric properties. We further optimized the electrical performances of the film when doping it with different molecular entities through secondary doping mechanisms, reaching n-type conductivities up to 4 S cm-1, and a power factor of 1.5 µW m-1 K-2. Finally, we integrated this system as active material in organic electrochemical transistors (OECT) to study the penetration of ions within this structured thin-film.

U.11.3
12:00 Discussion    
 
Photophysics III : Andrew Musser
15:00
Authors : Eliana Nicolaidou, Anthony W. Parker, Mike Towrie, Sophia C. Hayes*
Affiliations : Dept. of Chemistry, Univ. of Cyprus; Central Laser Facility, Rutherford Appleton Laboratory

Resume : Control over the conformation of conjugated polymers using nucleic acids (NAs) as templates can be very advantageous in inducing unique and readily controllable properties. Complexation of NAs with conjugated polyelectrolytes such as cationic polythiophenes (CPT) is facilitated by the presence of charged side groups on the backbone.[1] Previous studies on the biosensing ability of a certain CPT has revealed a tremendous impact of the ssDNA sequence on the conformational and optical response of the polymer.[2] The complex formed of CPT and oligocytosine (dC20) strands is especially noteworthy due to the formation of highly ordered and extended chains due to ?-stacking between the cytosine bases and thiophene rings, further stabilized by ?-stacking with the imidazole side chain.[3,4] This stands in contrast to the complex with oligoadenosine (dA20), where ?-stacking between the bases limits any stacking interactions with the polymer resulting in a flexible and torsionally disordered conformation. Interestingly, though, our previous ultrafast transient absorption (TA) work showed that both complexes showed only excitonic behavior, with similar and much faster decay dynamics compared to the polymer alone, which forms interchain aggregates.[4] Therefore, we used TRIR to directly probe the role of NA templating in the excited state species formed in the two complexes responsible for the faster dynamics observed with vis-nIR probes, as well as compare the photophysics of loosely bound complexes with the more rigid and ordered systems. We find that with excitation of the polymer in the visible (532 nm) both complexes form the P0 intrachain polaron evidenced by a broad absorption background that decays faster than the delocalized polaron DP1 formed in the case of CPT alone. The lower intensity of the P0 absorption in the CPT/dA20 case is consistent with increased intrachain disorder, while higher interchain long range order leads to the higher DP1 absorption.[5] The rigid complex formed in the case of CPT/dC20 limits the geometric relaxation observed in the C=C stretch Fano antiresonance, in agreement with our previous work.[4] Excitation in the UV (266 nm) shows that a charge transfer complex is formed between CPT and dC20 with the observation of the cytosine anion and a broad absorption background, in contrast to CPT/dA20 case, where the TRIR spectra solely reflect the excited state behavior of the oligoadenosine. These results show that non-covalent interactions between NAs and CPTs can determine the excited state species formed, which has implications to the applicability of these complexes in molecular electronics. 1. Rubio-Magnieto, J. et al, Soft Matter 2015, 11, 6460?6471. 2. Duan, X. R. et al, Acc. Chem. Res. 2010, 43, 260?270. 3. Charlebois, I. et al, Macromol. Biosci. 2013, 13, 717?722. 4. Peterhans, L. et al, Chem. Mater. 2020, 32, 7347?7362. 5. Pochas, C. M.; Spano, F. C. J. Chem. Phys. 2014, 140, 244902.

U.12.1
15:30
Authors : Luca Bondi , Beatrice Fraboni , Tobias Cramer
Affiliations : University of Bologna ; University of Bologna ; University of Bologna

Resume : Photoactive organic semiconductors are envisioned as a novel class of materials able to transduce light into stimulating signals inside biological cells or tissue [1]. The direct interface between the semiconductor and the electrolyte gives rise to different, competing electrochemical phenomena such as the photofaradaic or the photocapacitive processes, depending whether the photogenerated charges get involved in redox processes or accumulate at an interface. A detailed understanding of such chemical and photo-induced interactions is necessary to develop and optimize future devices. We addressed the problem in organic photoelectrodes considering both polymeric single-layer and organic molecular p/n junction thin-films [2]. Both are material systems that have been recently demonstrated to achieve the photomodulation of cardiac regeneration processes [3] or retinal neurons response [4]. By spectroscopic photovoltage and photocurrent measurements we gain insight into the energetics of the involved processes, while performing transient measurement we are able to identify the kinetics of light stimulated charge transfer processes. By combining these techniques with impedance spectroscopy, electric modelling and kinetic modelling, we identify the role of interfacial energy levels in the photoactivated processes and distinguish photocapacitive and photofaradaic contributions. The findings are further combined with nanoscale morphological investigations and Kelvin-Probe Force Microscopy leading to a quantitative interfacial energy diagram. We highlight how the energy diagram enables a comprehensive understanding of the photoelectrochemical reaction pathways and how the findings can be translated to predict the response of novel materials and devices, such as transducers based on floating semiconducting nanoparticles. [1] J. Hopkins, L. Travaglini, A. Lauto, T. Cramer, B. Fraboni, J. Seidel, and D. Mawad, ?Photoactive Organic Substrates for Cell Stimulation: Progress and Perspectives,? Adv. Mater. Technol., vol. 4, no. 5, pp. 1?10, 2019. [2] T. Paltrinieri, L. Bondi, V. ?erek, B. Fraboni, E. D. G?owacki, and T. Cramer, ?Understanding Photocapacitive and Photofaradaic Processes in Organic Semiconductor Photoelectrodes for Optobioelectronics,? Adv. Funct. Mater., vol. 2010116, 2021. [3] F. Lodola, V. Rosti, G. Tullii, A. Desii, L. Tapella, P. Catarsi, D. Lim, F. Moccia, and M. R. Antognazza, ?Conjugated polymers optically regulate the fate of endothelial colony-forming cells,? Sci. Adv., vol. 5, no. 9, 2019. [4] D. Rand, M. Jake?ová, G. Lubin, I. V?brait?, M. David-Pur, et al., ?Direct Electrical Neurostimulation with Organic Pigment Photocapacitors,? Adv. Mater., vol. 30, no. 25, pp. 1?11, 2018.

U.12.2
15:45
Authors : Frederic FAESE, Julien MICHELON, Xavier TRIDON
Affiliations : Neta; Neta; Neta

Resume : Historically, acoustic waves were first generated by piezoelectric materials [1]. To increase the spatial resolution of these waves, it is necessary to increase their frequency. Whereas the frequency of the acoustic waves generated by piezoelectric transducers is still limited to a few hundreds of MHz [2], this frequency can extend up to several hundreds of GHz for acoustic waves generated by femtosecond lasers [3]. That means that the sample thickness can be typically evaluated from a few microns to several millimeters with high-frequency transducers and from a few nanometers to several microns with picosecond ultrasonics that is based on femtosecond lasers. In this presentation, we will see how the embedded technology in Neta?s system opens high resolution mapping or massive data acquisition. Indeed, as a measurement only needs less than one second, a mapping can be considered. This significantly improves the speed of acquisition and leads to much more data for control itself or potential online inspection. After illustrating how the thickness of a layer can be evaluated, this presentation will focus on another possibility offered by Neta?s system: to determine the acoustic velocity in the material. Two practical applications will then be detailed: a multilayer W-TiN-SiO2 typical from MOS devices and a multilayer SiOx-SiNx typical from display components. [1] J. Bok and C Kounelis: "Paul Langevin (1872-1946)" Europhysics News 38.1, pp. 19-21, 2007. [2] Chen, Dongdong, et al. "Recent Development and Perspectives of Optimization Design Methods for Piezoelectric Ultrasonic Transducers." Micromachines 12.7, p. 779, 2021. [3] Pupeikis, Justinas, et al. "Picosecond ultrasonics with a free-running dual-comb laser." Optics Express 29.22, p. 35735-35754, 2021.

U.12.3
16:00
Authors : Somaiyeh Charoughchi, Hannes Hase, Jiang Tian Liu, Mohammad Askari, Venelin Petkov, Pat Forgione, Ingo Salzmann
Affiliations : Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada; Department of Physics, Concordia University, Montreal, Canada; Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada, Department of Chemistry, University of Toronto, Toronto, Canada; Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada; Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada; Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada; Department of Physics, Department of Chemistry and Biochemistry, Concordia University, Montreal, Canada;

Resume : The p-doping of organic semiconductors (OSC), that is conjugated organic molecules (COMs) and polymers (COPs), is generally done by using strong molecular acceptors as dopants. In principle, high doping efficiency is achieved with dopants of high electron affinity (EA) to promote electron transfer between COP/COM and the p-dopant. This leads to an increase in mobile charges (holes) in the COP/COM, which translates into an increase in conductivity. However, molecular p-doping of COMs/COPs with high ionization energy (IE) is a challenge as it requires p-dopants of similar EA. Common dopants of high EA (> 5 eV) are typically light-weight, unstable, show low solubility in common solvents with most COPs/COMs, and tend to diffuse through the semiconductor host. Furthermore, their planarity can lead to the formation of ground-state charge transfer complexes (CPXs) with the COPs/COMs, which is detrimental to the doping efficiency. Recently, a new generation of dopants has been introduced based on a cyclopropane core such as hexacyano-trimethylene-cyclopropane (CN6-CP) of high EA (5.87 eV) which is, however, highly unstable in air, and solvents and therefore largely unsuitable for practical applications. An analogue of CN6-CP, trimethyl 2,2?,2?-(cyclopropane-1,2,3-triylidene)-tris(cyanoacetate) (TMCN3-CP), has high EA (5.5 eV) and is suitable for solution processing techniques, but turned out to be unstable even under inert atmosphere. Here, we introduce a novel dopant 2,2',2''-(cyclopropane-1,2,3-triylidene)tris(2-(perfluorophenyl)acetonitrile) (3PFP3CN-CP) in which three of the nitrile groups of CN6-CP have been replaced by pentafluorophenyl groups. This dopant has an EA of 5.07 eV (determined by cyclic voltammetry) and a bulky, non-planar 3D structure which is poised to inhibit CPX formation with organic semiconductors. In aging experiments we have observed a remarkable stability of this dopant under inert atmosphere and first doping experiments juxtaposing the doping of poly- and oligothiophene evidence IPA for the former and the suppression of CPX formation for the latter, which occurs with planar dopants such as tetracyanoquinodimethane (TCNQ).

U.12.4
16:15 Discussion    
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Spectroscopy II : Steffen Duhm
09:00
Authors : Satoshi Kera
Affiliations : Institute for Molecular Science, Myodaiji, Okazaki 4448585, Japan

Resume : Understanding the impacts of weak electronic interaction on the electron delocalization is required to discuss the rich functionalities of organic molecular materials. Moreover, effects of the strong coupling of phonon (collective lattice vibration) and/or local molecular vibration to the electron must be unveiled. Angle-resolved UPS (ARUPS) is known to be a powerful technique to study the electronic structure. The HOMO-band features can offer a wide variety of key information, that is essential to comprehend charge-hopping transport (small-polaron related transport) [1] as well as to coherent band transport in the molecular single crystal [2,3]. However, the experimental study of fine features in the HOMO state has not been progressed till recently due to difficulty in the sample preparation, damages upon irradiation, and so on [4,5]. We present recent findings regarding on the precise measurements of the electronic structure of rubrene (C42H28) single crystals by using synchrotron-light based, high-resolution ARUPS. We describe the characteristic electronic structure of rubrene that 1) the UPS HOMO bands show a clear linear dichroism for bonding and anti-bonding HOMO, 2) a band-unfolding behavior as for intrinsic spectral function of HOMO, and 3) polaron-like quasiparticle effects on the electronic structure. The precise experiments of the 2D momentum scan in the ARUPS would provide a perspective of designing the organic semiconductor devices in non-trivial way. References [1] S. Kera, H. Yamane. N. Ueno, Prog. Surf. Sci. 84 (2009) 135-154. [2] N. Ueno and S. Kera, Prog. Surf. Sci. 83 (2009) 490-557. [3] Y. Nakayama, S. Kera, and N. Ueno, J. Mater. Chem. C 8 (2020) 9090-9132. [4] S. Machida, et al. Phys Rev. Lett. 104 (2010) 156401. [5] F. Bussolotti, et al., Nat. Comm. 8 (2017) 173.

U.13.1
09:30
Authors : Seungwook Choi, Guen Hyung Oh, Songwoung Hong, TaeWan Kim, Ansoon Kim
Affiliations : Operando Methodology and Measurement Team, Interdisciplinary Materials Measurement Institute, Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, South Korea; Department of Nano Science, University of Science and Technology (UST), Daejeon 34113, South Korea; Department of Electrical Engineering and Smart Grid Research Center, Jeonbuk National University, Jeonju, 54896, South Korea

Resume : Abstract Title : Operando XPS Investigation of Chemical State and Electronic Structure of MoTe2 Field-effect-transistor Depending on Channel Charge Accumulation Transition metal dichalcogenide field-effect transistors (TMD-FETs) could be one of next-generation transistors because they have novel material properties including high on-off ratio above 106, subthreshold swing of 140 mV/dec, Hall mobility around 10 cm2/Vs,1 and tunable bandgap depending on the number of layers. Among TMDs, MoTe2 is mainly studied to application for FETs and photodetectors because the minimal difference between band gaps of bulk and monolayer MoTe22, which is suitable for the FETs having high current on/off ratio3. Operando analysis enables to investigate the operation mechanism of devices from a material point of view under operating condition. In general, doping level and electronic structure of FET channel have been known to critically depend on the position of Fermi energy level (EF). In this presentation, we will introduce operando X-ray photoelectron spectroscopy (XPS) system including transistor probe stage and special sample holder built in ULVAC-PHI XPS system. Using the operando XPS, the chemical information and the electronic structure at the surface/interface of MoTe2-FET under device operation will be discussed. 1. N. R. Pradhan, D. Rhodes, S. Feng, Y. Xin, S. Memaran, B.-H. Moon, H. Terrones, M. Terrones and L. Balicas, ACS nano, 2014, 8, 5911-5920. 2. I. G. Lezama, A. Arora, A. Ubaldini, C. Barreteau, E. Giannini, M. Potemski and A. F. Morpurgo, Nano Lett., 2015, 15, 2336-2342. 3. H. Huang, J. Wang, W. Hu, L. Liao, P. Wang, X. Wang, F. Gong, Y. Chen, G. Wu and W. Luo, Nanotechnology, 2016, 27, 445201.

U.13.2
09:45
Authors : Ilaria Fratelli (1,2), Laura Basiricò (1,2), Andrea Ciavatti (1,2), John Anthony (3), Ioannis Kymissis (4) and 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 : In the last decade organic semiconductors have demonstrated to be excellent candidates for the development of a new class of X-Ray detectors able to fulfill important emerging requirements such as the mechanical flexibility, the possibility to cover large and curved surfaces, low-cost, and the possibility to operate at low-bias. Moreover, they are the only material platform that can offer human tissue equivalence, i.e. due to their chemical composition (i.e. low-Z elements) organic materials have radiation absorption comparable to that of human organs and tissues. This is a highly desirable property for a dosimeter to be employed in the medical field because it eliminates complex calibration procedures and the perturbation of the radiation beam when the detector is placed between the radiation source and the patient. On the other hand, the low-Z elements provide a poor absorption of high energy photons, limiting the efficiency of these detectors. To tackle this issue, one of the most effective strategies is based on the deep comprehension and enhancement of their detection mechanism based on a photoconductive gain effect (PG) [1], [2]. This effect is mediated by electrically active trap states which induce an inner amplification of the photocurrent generated by the absorption of high energy photons. Thus, a deep study of the trap states, both for minority and majority carriers in the organic thin film-based devices, permits tuning the PG and boosting the sensitivity of the detectors. The presence of traps in organic semiconductors has a profound impact on the performance of electronic devices. Their characterization, however, is still not trivial [3]. Here we present a new technique called Photocurrent Spectroscopy Optical Quenching to investigate the electrically active traps in organic-based devices for the detection of ionizing radiation. For this purpose, we employed flexible organic field effect transistors based on TIPS-Pn and TIPGe-Pn thin films. We deposited the organic semiconductors from solution by Pneumatic Nozzle Printing, [4] which allowed us to deposit organic thin films in a fully controlled way and to obtain very uniform and well-packed and aligned microcrystalline structures. Exploiting these devices, we investigated the origin of the active trap states ruling the photoconductive gain mechanism in tissue-equivalent, printed organic X-Ray detectors by Photocurrent Spectroscopy Optical Quenching experiments shining the devices with visible light at specific wavelengths during the X-Ray irradiation tests. Due to the interference of two distinct photoconductive gain mechanisms (i.e. one induced by visible photons, and the other by high energy photons) these measurements allow us to identify the excitonic states responsible for the activation of the X-Ray induced PG and to justify the different detecting performances achieved with different organic molecules. References [1] L. Basiricò, et al., Nat. Commun., vol. 7, no. 1, p. 13063, Dec. 2016, doi: 10.1038/ncomms13063. [2] I. Temiño et al., Nat. Commun., vol. 11, no. 1, pp. 1?10, 2020, doi: 10.1038/s41467-020-15974-7. [3] H. F. Haneef, et al., J. Mater. Chem. C, vol. 8, p. 759, 2020, doi: 0.1039/c9tc05695e. [4] S. Yang, et al., Adv. Electron. Mater., vol. 4, no. 6, pp. 4?9, 2018, doi: 0.1002/aelm.201700534.

U.13.3
10:00
Authors : Imran , Do-Hyeun Kim, Bong Seon Jong, Su-Young Chi, and Choi Yo Han
Affiliations : Department of Computer Engineering, Jeju National University, Jeju 63243, Korea ; Korea University of Science and Technology, 21 7,Gajeong-ro,Youseong-gu, Daejeon, Korea; Electronics and Telecommunications Research Institute, Dajeon,305-370, Korea;

Resume : Authoring tools based on data-driven sciences is a hot research topic for researchers of big chemical data. However, several challenges prevent advancement in data-driven materials science, such as data integrity, experimental and computational data integration, data standardization, and the gap between academic efforts and industrial interests. In material science, materials data is derived from big data sources that are too complicated for common human reasoning and materials applications. Hence, there is a vital need to develop simulation and authoring tools to meet the challenges of raw big chemical data. This paper proposes a material relationship analysis-based authoring system for high-performance properties material discovery. The relationship analysis system recommends high-performance index material data based on correlation analysis. Correlation analysis is used to find the relationship between material data features of components, processes conditions, and performance index properties. A web-based relationship analysis authoring tool was developed to evaluate the proposed relationship analysis mechanism for material discovery. Data visualization mechanisms of the developed authoring and analysis system are used to visualize the output of relationship analysis using data tables and heatmaps-based correlation analysis. Furthermore, the data table-based relationship analysis results are used to recommend high-performance properties-based material discovery. The material discovery results depict that the proposed relationship analysis system will fill the research gaps of screening and accelerating new stable materials.

U.13.4
10:15 Discussion    
10:30 Break    
 
Advanced Microscopies 2 : Steffen Duhm
11:00
Authors : Yuhan Zhong (1,2), Shubhradip Guchait (1), Viktoriia Untilova (1), Laurent Herrmann (1), Dominique Müller (2), Céline Kiefer (3),Thomas Heiser (2), Martin Brinkmann (1)
Affiliations : (1) Université de Strasbourg, CNRS, ICS UPR 22, F-67000 Strasbourg, France (2) Université de Strasbourg, CNRS , ICUBE UMR 7357, F-67000, Strasbourg, France (3) Université de Strasbourg, CNRS, IPCMS UMR 7504, F-67087 Strasbourg, France

Resume : Doping of polymer semiconductors is a central topic in plastic electronics and especially in the design of new better performing thermoelectric materials. Sequential doping of highly ordered polymer semiconductors is widely used to tune the charge carrier density that determines the thermoelectric properties. Various studies have demonstrated that dopant molecules intercalate into the layers of side chains in the crystals of polymer semiconductors.(1-3) It is therefore essential to clarify the way dopants are incorporated into the crystal lattice of the pristine polymer and how this is related to the dopant size and electron affinity. A combination of electron diffraction and polarized UV-vis-NIR spectroscopy on highly oriented P3HT and PBTTT thin films allows to quantify the amount of intercalated dopant molecules as well as the molecular orientation of dopants such as F4TCNQ, F6TCNNQ with respect to the polymer chains. A mapping of the orientational distribution of dopant molecules in the polymer crystal can thus be obtained. In the case of P3HT/F6TCNNQ, modeling of the diffraction patterns of doped crystals identifies the stoichiometry of the doped polymer phase and confirms the dopant orientation obtained from spectroscopy measurements as well as the lattice parameter variation induced by intercalation. In the case of Magic blue, Rutherford Backscattering is used to quantify the dopant amount in the films, Polarized UV-vis-NIR helps determine the diffusion coefficients of the dopant into the P3HT matrix whereas TEM demonstrates preferential location of MB in the amorphous phase of P3HT. It is demonstrated that the highest charge conductivities (up to 3000 S/cm) are observed in oriented P3HT films when the amorphous phase of P3HT is selectively doped with MB. References. (1) Untilova, V.; Biskup, T.; Biniek, L.; Vijayakumar, V.; Brinkmann, M. Control of Chain Alignment and Crystallization Helps Enhance Charge Conductivities and Thermoelectric Power Factors in Sequentially Doped P3HT:F4TCNQ Films. Macromolecules 2020, 53 (7), 2441?2453. (2) V. Untilova, H. Zeng, P. Durand, P. Allgayer, L. Herrmann, N. Leclerc and M.Brinkmann. Intercalation and ordering of F6TCNNQ and F4TCNQ dopants in regioregular poly(3-hexylthiophene) crystals: impact on anisotropic thermoelectric properties of oriented thin films Macromolecules 2021, 54, 13, 6073-6084. (3) Vijayakumar, V.; Zhong, Y.; Untilova, V.; Bahri, M.; Herrmann, L.; Biniek, L.; Leclerc, N.; Brinkmann, M. Bringing Conducting Polymers to High Order: Toward Conductivities

U.14.1
11:30
Authors : Filipe Richheimer1,2, David Toth3,4, Bekele Hailegnaw5,6, Mark A. Baker2, Robert A. Dorey2, Ferry Kienberger3, Fernando A. Castro1, Martin Kaltenbrunner6, Markus C. Scharber5, Georg Gramse3,4, Sebastian Wood1
Affiliations : 1National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK; 2Centre for Engineering Materials, University of Surrey, Guildford, GU2 7XH, UK; 3Keysight Technologies GmbH, Linz, 4020, Austria; 4Applied Experimental Biophysics, Johannes Kepler University, Linz, 4020, Austria; 5Linz Institute for Organic Solar Cells, Johannes Kepler University, Linz, 4040, Austria; 6Department Soft Matter Physics, Johannes Kepler University Linz, 4040, Austria

Resume : Hybrid organic-inorganic halide perovskites (OIHPs) are a class of direct band gap semiconductors with attractive optoelectronic and material processing characteristics for use as an absorber material in next-generation photovoltaics. OIHP based solar cells already exhibit power conversion efficiencies comparable to crystalline silicon cells and potential for high performance tandem devices through band-gap tuneability and solution-based processing. Thus far, a major limiting factor for the widespread commercial breakthrough of this technology has been the limited operational stability. A contributing factor to performance losses during photovoltaic operation is charge redistribution effects, such as the migration of mobile ions, which can facilitate local phase changes in the OIHP active layer. These charge redistribution effects can be further promoted by the film microstructure, which in case of the typical polycrystalline film morphology of OIHP films is dominated by defect-rich grain boundaries. The resulting interplay between the film morphology and charge redistribution effects occurs over typical length scales of tens of nanometres, thus demanding advanced characterization techniques to study the connection between local charge imbalance and subsequent material instability under operational conditions. Herein, we employed advanced (time-resolved) electrical modes of scanning probe microscopy (SPM) to probe early-stage degradation in triple-cation mixed-halide OIHPs. Using the SPM platform under controlled inert environment, we were able to induce localised electrical bias stresses simulating photovoltaic operation and subsequently probe the system response with high spatial resolution. We observed the formation of nanometric sized grain structures at the film surface, which displayed a variety of coverage densities and spatial distributions depending on the bias and photoexcitation conditions employed. We link the emergence of such nanograin structures to a localised charge build-up at the film grain boundaries, which in turn facilitates the local perovskite phase decomposition, leaving behind lead halide nanostructures. These findings establish a direct link between charge redistribution effects (contributed by ion migration) and local phase decomposition. We propose the use of novel strategies for inhibiting charge accumulation effects at grain boundaries in order to prevent the initiation of these operational degradation pathways.

U.14.2
11:45
Authors : Nadezda Prochukhan, Michael A. Morris.
Affiliations : Nadezda Prochukhan - School of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin 2, Ireland; BiOrbic?Bioeconomy SFI Research Centre, University College Dublin, Belfield, Dublin 4, Ireland; Michael A. Morris - School of Chemistry, CRANN and AMBER Research Centres, Trinity College Dublin, College Green, Dublin 2, Ireland; BiOrbic?Bioeconomy SFI Research Centre, University College Dublin, Belfield, Dublin 4, Ireland.

Resume : Advanced microscopy characterization methods have been widely utilized to characterize inorganic materials such as semiconductors. However, it is important to adapt these tools for soft materials to gain structural information required for novel cutting-edge technologies. We report on advanced microscopic techniques such as atomic force microscopy (AFM), He-Ion microscopy (HIM), scanning electron microscopy (SEM) and focused ion beam (FIB) 3D reconstructions methods for optimum characterization of soft materials. In particular, we adapted electron microscopy techniques at low operating voltages to avoid structural degradation. HIM was optimised for operation with charge compensation. AFM techniques were adapted to probe topographical features of very smooth and highly rough surfaces of soft materials (rough-mean-square values up to 0.5 µm). Furthermore, we demonstrate how FIB can be used to model structural density of fibrous materials and derive quantifiable data such as pore density and tortuosity (or the expected flow path through the pores) using simple methodologies using open-source software. Sample preparation for these microscopic techniques is also detailed. We focus on polymeric materials such as polymethyl methacrylate (PMMA), biopolymer materials such as lignin and chitosan and natural materials such as wood (pine, beach, oak, walnut, eucalyptus). The development of the advanced microscopic techniques for soft materials will open up new avenues for research possibilities and novel applications [1]. [1] I. E. McCarroll, P. A. J. Bagot, A. Devaraj, D. E. Perea, and J. M. Cairney, ?New frontiers in atom probe tomography: a review of research enabled by cryo and/or vacuum transfer systems,? Mater. Today Adv., vol. 7, p. 100090, Sep. 2020, doi: 10.1016/J.MTADV.2020.100090.

U.14.3
12:00 Discussion and Closing Remarks    

No abstract for this day


Symposium organizers
Emanuele ORGIUInstitut national de la recherche scientifique – University of Québec

1650 Blvd. Lionel Boulet, Varennes (Québec), J3X 1S2, Canada

+1 514 228 6908
emanuele.orgiu@inrs.ca
Ingo SALZMANNConcordia University

Department of Physics, Department of Chemistry& Biochemistry 7141 Sherbrooke St. West, Montreal (Québec), H4B 1R6, Canada

+1-514 848 2424 ext. 4774
ingo.salzmann@concordia.ca
Natalie BANERJIUniversity of Bern

Department of Chemistry and Biochemistry Freiestrasse 3, CH-3012 Bern, Switzerland

+41 31 631 43 22
natalie.banerji@dcb.unibe.ch
Steffen DUHM Soochow University

Institute of Functional Nano & Soft Materials (FUNSOM), 199 Ren-Ai Road, Suzhou 215123, P. R. China

+86 512 6588 0371
duhm@suda.edu.cn