preview all symposia

Hybrid, organic and bio-materials


Computational modelling of organic semiconductors: from the quantum world to actual devices

Modelling organic semiconductors plays a crucial role for advancing organic electronics. By now the used methods have become exceedingly divers, which calls for a platform where scientists from the various involved areas can discuss their findings and link their expertise in hither to unexplored ways.



Using various types of advanced simulation approaches, tremendous insight into the properties of organic semiconductor materials and their application in devices has been generated. The great variety of the encountered problems requires the use of a very diverse pool of techniques ranging from highly-correlated quantum-chemistry approaches and band structure calculations (in many cases including many-body corrections) to more macroscopic techniques including molecular dynamics, coarse-grained, or micro-electrostatic modelling. For understanding the dynamics of charges and excitons or to analyze the formation of heterogeneous phases, statistical approaches including Monte-Carlo techniques are typically applied and, for understanding devices at their full level of complexity, drift-diffusion based calculations become necessary.

Recently, there has been a strong drive to combine these approaches in a hierarchical fashion, e.g., to use the results of molecular-dynamics modelling on complex structures as input for the quantum-mechanical simulation of electronic or optical properties. Beyond that, first attempts to establish tightly integrated multi-scale schemes are under way.

As a consequence, involved scientists typically have very diverse scientific backgrounds. This calls for the establishment of a platform for exchanging ideas, recent insights, and also the knowledge on specific computational tools. To aid in that, this symposium

(i) aims at providing an as comprehensive as possible overview of the strengths and limitations of modelling approaches used for describing organic semiconductors including the latest directly relevant methodological developments;

(ii) it will portray recent efforts in hierarchical and truly multi-scale modelling of these materials; and

(iii) above all, the symposium will provide a possibility for showcasing the insight into the intrinsic processes in organic semiconductors and devices that can be gained from computational studies.


Hot topics to be covered by the symposium:

spanning the length-scales:

  • highly-correlated quantum-chemical and post density-functional theory methods
  • quantum-mechanical techniques used for simulating complex structures
  • molecular dynamics and coarse-graining applied to disordered and heterogeneous structures
  • Monte Carlo techniques for simulating dynamics and growth
  • simulation of device-structures at their full level of complexity by drift-diffusion based approaches
  • hierarchical combination of simulations at multiple length-scales and true multi-scale modelling

phenomena in the focus of interest include (but are not limited to):

  • understanding (charge-transfer) exciton formation/dissociation at hetero-interfaces
  • modelling carrier injection/abstraction at electrodes
  • quantifying the impact of disorder
  • simulating dynamic processes from fs to minutes
  • applying multi-scale approaches to charge-transport and exciton diffusion
  • modelling film growth and phase dynamics
  • understanding the impact of film heterogeneities on device performance



Invited speakers will be asked to submit feature articles as contributions to a special issue of Advanced Functional Materials. These will, naturally, be subject to strict peer reviewing.


Members of scientific committee (confirmed):

  • Jean-Marie André, University of Namur, Belgium
  • Jean-Luc Brédas, Georgia Institute of Technology, Atlanta, USA
  • Gian Paolo Brivio, Universitá di Milano-Bicocca, Milano, Italy
  • Paulette Clancy, Cornell University, Ithaca, USA
  • Jerome Cornil, University of Mons, Belgium
  • Claudia Draxl, Humboldt-Universität zu Berlin, Germany
  • Dago de Leeuw, Max Planck Institute for Polymer Research, Mainz, Germany
  • Elisa Molinari, CNRNano, Modena, Italy
  • Mark Ratner, Northwestern University, Evanston, USA
  • Zhigang Shuai, Tsinghua University, PR China
  • Nobuo Ueno, Chiba University, Chiba, Japan


Invited speakers (confirmed):

  • Denis Andrienko, Max Planck Institute for Polymer Research, Germany
  • David Beljonne, Université de Mons, Belgium
  • Clemence Corminboeuf, EPFL Lausanne, Switzerland
  • Reinder Coehoorn, Philips Research Laboratories, The Netherlands
  • Gianaurelio Cuniberti, TU Dresden, Germany
  • Kristen A. Fichthorn, Penn State University, USA
  • Geoffrey Hutchison, University of Pittsburgh, USA
  • Hiroyuki Ishii, University of Tsukuba, Japan
  • Jan Anton Koster, Rijksuniversiteit Groningen, The Netherlands
  • Lingyi Meng, Xiamen University, PR China
  • Jeff B. Neaton, Lawrence Berkeley National Lab, USA
  • Chad Risko, Georgia Institute of Technology, USA
  • Alice Ruini, Università degli Studi di Modena e Reggio Emilia, Italy
  • Alexander L. Shluger, University College London, Great Britain
  • Zoltán G. Soos, Princeton University, USA
  • Alexandre Tkatchenko, Fritz Haber Institute of the Max Planck Society, Germany
  • Claudio Zannoni, Universitá di Bologna, Italy




   Quantum Wise


Symposium organizers:


Egbert Zojer
Institute of Solid State Physics
Graz University of Technology
Petersgasse 16
8010 Graz
Phone: +43 316 873 8475
Fax: +43 316 873 8466

Leeor Kronik
Department of Materials and Interfaces
Weizmann Institute of Science
Rehovoth 76100
Phone: +972 8 9344993
Fax: +972 8 9344138

Georg Heimel
Institut für Physik, Humboldt-Universität zu Berlin
Brook-Taylor-Straße 6
12489 Berlin
Phone: +49 30 2093 7537
Fax: +49 30 2093 7443

Start atSubject View AllNum.Add
Authors : G. Volonakis (1), L. Tsetseris (2), S. Logothetidis (1)
Affiliations : (1) Lab for Thin Films, Nanosystems and Nanometrology, Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece; (2) Department of Physics, National Technical University of Athens, Athens, Greece

Resume : Over the last years, the power conversion efficiency of organic photovoltaics (OPVs) is continuously rising and has recently reached values larger than 11%. However, exposure of OPVs to ambient conditions is known to significantly deteriorate the performance of the devices. Yet the atomic-scale details and mechanisms that govern this degradation remain unclear. Here we employ first-principles calculations based on the density-functional theory to (a) reveal the favorable defective configurations formed when O2 and H2O molecules intrude the molecular crystals of prototype OPV semiconductors P3HT and PCBM and (b) to find the effects of such impurities on the electronic properties of the materials. Specifically, molecular H2O is found to physisorb intact with minimal effects on the electronic properties. On the other hand, our results show that O2 can either physisorb intact or may chemisorb and dissociate on PCBM and P3HT. We thus identify the preferable configurations, in agreement with pertinent experimental data. These conformations are found to create states inside the band gaps, which can act as charge carrier traps (deep and shallow) or as charge recombination centers and consequently are expected to have detrimental effects on the performance of the materials. The reported defective configurations are consistent with available reports on oxidation of both materials. These results help clarify the role of O2 and H2O impurities on the degradation mechanisms in OPVs.

Authors : C.A. Rozzi (1), M. Amato, A. Rubio (2), and E. Molinari (1,3)
Affiliations : (1) Istituto Nanoscienze - CNR, Centro S3, 41125 Modena, Italy; (2) Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Universidad del País Vasco, Centro de Física de Materiales CSIC-UPV/EHU-MPC and DIPC, 20018 San Sebastián, Spain; (3) Dipartimento di Scienze Fisiche, Matematiche e Informatiche, Università di Modena e Reggio Emilia, via Campi 213a, 41125 Modena, Italy.

Resume : The initial quantum dynamics leading to electron transfer from the photoexcited polymer to the fullerene in P3HT-PCBM is investigated ab-initio by time-dependent density functional theory simulations. We find coherent electron transfer between donor and acceptor and oscillations of the transferred charge with a period matching that of observed vibrational modes in ultrafast optical spectroscopy [1]. Our results show that the coherent coupling between electronic and nuclear degrees of freedom is of key importance in triggering charge delocalization and transfer not only in covalently bonded molecules [2] but also in this prototype non-covalently bonded system of relevance for photovoltaics. [1] SM Falke, CA Rozzi, D Brida, M Amato, A De Sio, A Rubio, G Cerullo, E Molinari, and C Lienau, submitted. [2] CA Rozzi, SM Falke, N Spallanzani, A Rubio, E Molinari, D Brida, M Maiuri, G Cerullo, H Schramm, J Christoffers, C Lienau, Quantum coherence controls the charge separation in a prototypical artificial light-harvesting system, Nat Commun 4, 1602 (2013).

Authors : Gabriele D'Avino and Matthieu J. Verstraete
Affiliations : Université de Liège, Institut de Physique, Allée du 6 Août, 17 Sart-Tilman, B-4000 Liège, Belgium

Resume : Mixed-stack charge transfer (CT) crystals (e.g. TTF-CA) are one of the few examples of ferroelectrics among organics materials [1]. In these quasi-1D systems, electron donor (D) and acceptor (A) molecules pack in an alternating pattern, DADA, and a fractional charge, q, is transferred from D to A. In some systems, a lattice instability is triggered by the increase of CT above the neutral-ionic boundary (q~0.5), leading to a low-temperature polar phase (Tc=81 K in TTF-CA). We present a detailed theoretical investigation on a novel series of hydrogen-bonded CT crystals, for which room temperature ferroelectricity has been claimed [2]. Our analysis is based on the Peierls-Hubbard model, which proved successful in describing the transition in different CT crystals [3]. A novel approach to the model parameterization, based on first-principle calculations, is here proposed, and its accuracy validated by reproducing the transition of TTF-CA. Our calculations show that, contrary to what was originally reported, the CT crystals in [2] are all largely neutral (q<0.1) and hence very unlikely to present a polar lattice. Experimental data reported in [2] confirm our estimate for q and do not allow one to draw a definitive conclusion about the ferroelectricity of these materials. [1] S. Horiuchi, Y. Tokura, Nature Materials 7, 357 (2008); [2] A. Tayi et al., Nature 488, 485 (2012); [3] G. D’Avino et al., Phys. Rev. Lett. 99, 156407 (2007); G. D’Avino et al., Phys. Rev. B 83, 161105R (2011);

Start atSubject View AllNum.Add
Modelling Interfaces I : Alice Ruini
Authors : David Gao, Matthew Watkins, Alexander Shluger
Affiliations : Department of Physics and Astronomy, University College London, UK

Resume : We will discuss the results of theoretical modelling of adsorption of individual organic molecules and molecular aggregates at insulating surfaces motivated by high resolution non-contact AFM imaging of surface structures. We aim at understanding how the molecular structure, the polar end-groups, as well as the substrate lattice constant and ionic species influence the formation of supra-molecular networks on insulating surfaces. As one such example, we discuss differences in the adsorption, binding, and mobility of Co-Salen molecules at NaCl and NiO (001) surfaces and the theoretical methods used in these studies. As the second example, we present the results of modelling the assembly of CDB molecules at several alkali halide surfaces. These, much larger molecules are composed of a central aromatic part surrounded by two lateral decyloxy chains (O-(CH2)9-CH3). The central part consists of three phenyl rings ended by cyano (CN) groups. We are developing multi-scale methodology for modelling the structure and growth of such networks. This includes embedded cluster QM molecular dynamics of molecules at surfaces, which is used for Genetic Algorithm powered development of force-fields for molecule-surface interactions. These force-fields are then used for modelling the atomistic structure and dynamics of larger aggregates of molecules at surfaces. This information is used for modelling AFM images of surface structures and the mechanisms of their assembly, including the effect of surface defects.

Modelling Charge Transport I : Hiroyuki Ishii
Authors : Gianaurelio Cuniberti Frank Ortmann Sebastian Radke
Affiliations : Institute for Materials Science, Max Bergmann Center of Biomaterials, and Center for Advancing Electronics Dresden, TU Dresden, 01062 Dresden, Germany

Resume : Novel organic materials are at the focus of current experimental and theoretical activities in order to improve the efficiency of their charge transport characteristics. Theory can provide guidelines to realize high mobility materials either through a molecular picture or through simulations of condensed phases. While the molecular point of view can provide some qualitative tendencies, significant improvements however have still to be accomplished to achieve predictive power of transport simulations in real devices. We present here recent work on transport simulations in organic materials by combining high level electronic structure calculations with molecular dynamics simulations to parametrize effective models for charge transport. Especially the influence of static and dynamical disorder in the electronic structure of the organic systems on the charge mobilities will be addressed.

Authors : Denis Andrienko
Affiliations : Max Planck Institute for Polymer Research

Resume : Interest in the field of organic electronics is largely provoked by the possibility to fine-tune properties of organic semiconductors by varying their chemical structure. Often, compound design is solely guided by chemical intuition, even though material development would benefit from more rigorous structure-property relationships, which link the chemical structure, material morphology and macroscopic properties. To formulate such relationships, an understanding of physical processes occurring on a microscopic level as well as the development of methods capable of scaling these up to macroscopic dimensions are required [1]. The aim of computer simulations is to facilitate this by zooming in on the behavior of electrons and molecules and by bridging micro- and macroscopic worlds. Here, we describe the current status of methods which allow the linking of molecular electronic structure and material morphology to the mesoscopic/microscopic dynamics of charge carriers and excitons. Special attention is paid to the challenges these methods face when aiming at quantitative predictions [2,3]. [1] V. Ruehle, A. Lukyanov, F. May, M. Schrader, T. Vehoff, J. Kirkpatrick, B. Baumeier, D. Andrienko, J. Chem. Theory Comput., 3335-3345, 2011 [2] F. May, B. Baumeier, C. Lennartz, D. Andrienko, Phys. Rev. Lett., 109, 136401, 2012 [3] M. Schrader, R. Fitzner, M. Hein, C. Elschner, B. Baumeier, M. Riede, K. Leo, P. Baeuerle, D. Andrienko, J. Am. Chem. Soc., 134, 6052-6056, 2012

Authors : P. Vancsó (1,4), G. I. Márk (1,4), D. Kvashnin (2), V. A. Demin (2), L. Chernozatonskii (2), Ph. Lambin (3), A. Mayer (3) and L. P. Biró (1,4)
Affiliations : (1) Institute of Technical Physics and Materials Science, Research Centre for Natural Sciences, PO Box 49, H-1525 Budapest, Hungary,; (2) N.M.Emanuel Institute of Biochemical Physics, Russian Academy of Sciences (IBCP), 4 Kosygin St., Moscow, 119991, Russian Ferderation; (3) Department of Physics of Matter and Radiation, University of Namur (FUNDP) 61, Rue de Bruxelles, B-5000 Namur, Belgium; (4) Korean-Hungarian Joint Laboratory for Nanosciences, PO Box 49, H-1525 Budapest, Hungary

Resume : According to our recent massive DFT simulations, when creating holes in a bilayer graphene, the two layers tend to zip together along the edges. This phenomenon has also been recently observed by transmission electron microscopy (TEM) [1]. If the holes are arranged periodically, the optimized structure turns to be a carbon nanotube superlattice like closed sp2 carbon network. By varying the size and distance of the holes, a very rich configuration space of systems with diverse electronic structures can be created, which includes both conducting and localized states. Utilizing our wave packet dynamical simulation code [2] we studied the local time- and energy dependent dynamics of the system. By comparing the results using a jellium potential and a local pi-band pseudopotential [3] we were able to separate the geometrical and electronic structure effects, which are intermixed in the band structure. [1] G. Algara-Siller, et al., Carbon 65 (2013) 80-86 [2] G. I. Mark, et al., Phys. Rev. B 85(2012) 125443 [3] A. Mayer, Carbon 42, (2004) 2057

Authors : Jérôme Cornil, Victor Geskin, and Colin Van Dyck
Affiliations : University of Mons Laboratory for Chemistry of Novel Materials

Resume : Understanding the alignment of molecular orbitals and corresponding transmission peaks with respect to the Fermi level of the electrodes is a major challenge in the field of molecular electronics. In order to design functional devices, it is of utmost importance to assess whether controlled changes in the electronic structure of isolated compounds are preserved once they are inserted in the molecular junctions. We shed light here on this central issue by performing Density Functional Theory calculations on junctions including diarylethene-based molecules. We demonstrate that the chemical potential equalization principle allows us to rationalize the existence or not of a Fermi level pinning (i.e., same alignment in spite of varying ionization potentials of the isolated compounds) and points to the essential role played by Metal Induced Gap States (MIGS). We also evidence that the degree of level pinning is intimately linked to the degree of orbital polarization when a bias is applied between the two electrodes. C. Van Dyck et al., PhysChemChemPhys

Authors : Bitam Said, Abdelbaki Djebaili
Affiliations : Faculty of Sciences, University of Batna, -05000, Algeria

Resume : Investigation of the geometric and electronic structure of the polyacetylene with substituent’s of different strengths of donor and acceptor functional groups was carried out with 3-21G basis sets, by incorporating The rates of this geometrical isomerization and Arrhenius parameters. In the case of unsubstituted polyacetylene as the reference.. The values of the equilibrium constant for the reaction have also been determined at various temperatures between 300 and 500 K and the value of the energies change calculated. The results demonstrate that the isomerization energies are positive and the barrier heights ∆Ebarrier are expected to be sensitive for the magnitude of substituents effects. Keywords: polyacetylene, rate constant, equilibrium constant.

Authors : Haoyuan Li,Lian Duan* and Yong Qiu
Affiliations : Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, China

Resume : The time-of-flight (TOF) and dark-injection space-charge-limited current (DI-SCLC) measurements are both widely used to obtain the charge mobility in organic semiconductors. However, the charge transport in these cases is still not fully understood. In the TOF measurement, when the carrier density cannot be neglected, the current is said to be space-charge-perturbed (SCP). The effect of space-charge perturbation on the extracted charge mobility is unclear. The commonly assumed conclusion that the peak time in the DI-SCLC measurement equals 0.787 times the transit time in the TOF measurement also lacks validation for organic semiconductors. Using multi-particle Monte Carlo simulations, we have studied the transient currents in organic materials, under conditions varying from space-charge-free (SCF) to space-charge-limited (SCL). The results suggest that the SCP effect is shorter peak time and longer transit time. This conclusion has been confirmed by experiment. For transient SCL currents, the peak time is found to be much shorter than previously thought for systems with large energetic disorders. These results can be explained by the enhanced charge transport by higher carrier density and the non-uniform electric field, which is stronger at the carrier packet front and weaker at the injection part.

Authors : Chen Li, Lian Duan*, Haoyuan Li, Yongduo Sun, Yong Qiu
Affiliations : Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing, 100084, China

Resume : In order to unravel the effect of trap energy on carrier transport in organic disorder semiconductors, a comprehensive study was conducted on hole transport in a series of organic molecular hosts with explicit traps at different trap energies. The mobility measured by time-of-flight experiments was found to decrease significantly at shallow trapping, but hardly decreased at deep trapping, where a sharp decrease of carrier density was observed. By analyzing temperature dependence of the mobility, the decreased mobility at shallow trapping were found to originate from increased energetic disorder and activation energy, whereas both energetic disorder and activation energy are changeless at deep trapping. We find it reasonable to cover the different effects of deep trapping and shallow trapping in a universal mechanism based on the Miller-Abrahams hopping model, and carrier out multiple-carrier Monte Carlo simulations to elaborate how, within this universal mechanism, that deep and shallow traps affect energetic disorder, transporting trajectories and carrier density in different ways. The results suggest transporting at shallow trapping always involve in a multiple-trapping-release process owing to frequent thermal reactivation, thus lead to winding transporting trajectory, increased effective energetic disorder and increased activation energy; while deep traps tend to immobilize the carriers and act as ionized scattering centers, thus mainly decrease the carrier density and just elongate the trajectory slightly. Investigating the change of mobility with continuous trap energy suggests a transition region, rather than a strict borderline exists between deep traps and shallow traps, and in this region carrier transport is controlled by both deep traps and thermal reactivation from shallow traps. These results will be of great value for understanding of the mechanisms, as well as designing of the devices in organic electronics. References: The Journal of Physical Chemistry C, Under review. The Journal of Physical Chemistry C 2012, 116, 19748-19754.

Start atSubject View AllNum.Add
Drift-Diffusion Simulations : Reinder Coehoorn
Authors : L.J.A. Koster
Affiliations : Zernike Institute for Advanced Materials University of Groningen Nijenborgh 4 9747 AG Groningen

Resume : The performance of organic bulk heterojunction solar cells is strongly dependent on the donor/acceptor morphology. The tremendous complexity of this morphology makes it difficult to include morphological effects in numerical device models. In this talk, I will show an extension of 1D approaches to include morphological effects and introduce a fully 3D drift-diffusion model. 1D drift-diffusion approaches treat the blend of acceptor and donor materials as one effective medium. This model can describe the current-voltage characteristics in terms of basic physics and material parameters but is silent on morphology. Inhomogeneities in the film can be included by sub-dividing the active layer into regions that can be treated in 1D separately. In this way, the effect of fullerene clusters in a polymer/fullerene blend can be described by treating the polymer-rich regions and the fullerene clusters separately. The 3D nanoscale morphology of polymer/zinc oxide solar cells was used as a direct input into a fully 3D optoelectronic model. This model includes the effects of exciton diffusion and quenching; space-charge; interfacial charge separation and recombination; and drift and diffusion of charge carriers. Given the experimental morphologies, the corresponding differences in performance could be reproduced with a single set of parameters. Several morphological aspects that determine the efficiency are discussed and compared to other organic solar cells.

Start atSubject View AllNum.Add
Authors : Claudia Caddeo (1,2), Alessandro Mattoni (2)
Affiliations : (1) Universita degli Studi di Cagliari, Dipartimento di Fisica, Cittadella Universitaria, 09042 Monserrato; (2) Istituto Officina dei Materiali del Consiglio Nazionale delle Ricerche (CNR-IOM), c/o Dipartimento di Fisica, Cittadella Universitaria, 09042 Monserrato

Resume : Since polymer-based devices are typically synthesized from solution, the polymer solubility plays a crucial role in determining their performances: for example, in solution processed poly(3-hexylthiophene) transistors the field effect mobility is markedly different depending on the polymer miscibility in solvents[1]. The prediction of the solubility properties via atomistic simulations is an interesting challenge, but only few works exist on the topic. We apply the Flory-Huggins theory (that is typically used to study the miscibility of macromolecules[2]) for the first time to study the solubility of conjugated conducting polymers in a typical organic solvent via atomistic simulations. The properties of the isolated solvent and polymer are correctly reproduced, and the calculated solubilities of the oligo(3-alkylthiophene)s in tetrahydrofuran as a function of their side chains lengths are in agreement with available experimental data. Present investigation shows that the atomistic approach based on molecular dynamics is a powerful tool to study the solubility of alkylthiophenes in molecular solvents[3]. [1] J.-F. Chang et al., Chem. Mater. 2004, 16,4772-4776 [2] P. J. J. Flory, J. Chem. Phys. 1942, 10, 51 [3] C. Caddeo et al., Macromolecules 2013, 46 (19), 8003-8008


No abstract for this day