Simulations Of Charge Transport In Organic Compounds
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Simulations Of Charge Transport In Organic Compounds
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Author : Thorsten Vehoff
language : en
Publisher: Sudwestdeutscher Verlag Fur Hochschulschriften AG
Release Date : 2010
Simulations Of Charge Transport In Organic Compounds written by Thorsten Vehoff and has been published by Sudwestdeutscher Verlag Fur Hochschulschriften AG this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
To aid the design of organic semiconductors, we study the charge transport properties of organic liquid crystals and single crystals. The aim is to find structure-property relationships linking the chemical structure as well as the morphology with the bulk charge carrier mobility of the compounds. To this end, molecular dynamics (MD) simulations are performed yielding realistic equilibrated morphologies. Partial charges and molecular orbitals are calculated using quantum chemical methods. The molecular orbitals are then mapped onto the molecular positions and orientations, which allows calculation of the transfer integrals between nearest neighbors using the molecular orbital overlap method. Thus realistic transfer integral distributions and their autocorrelations are obtained. In case of organic crystals two descriptions of charge transport, namely semi-classical dynamics (SCD) and kinetic Monte Carlo (KMC) based on Marcus rates, are studied. In KMC one assumes that the wave function is localized on one molecule, while in SCD it is spread over a limited number of neighboring molecules. The results are compared amongst each other and, where available, with experimental data.
Simulations Of Charge Transport In Organic Compounds
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Author :
language : en
Publisher:
Release Date : 2010
Simulations Of Charge Transport In Organic Compounds written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
To aid the design of organic semiconductors, we study the charge transport properties of organic liquid crystals, i.e. hexabenzocoronene and carbazole macrocycle, and single crystals, i.e. rubrene, indolocarbazole and benzothiophene derivatives (BTBT, BBBT). The aim is to find structure-property relationships linking the chemical structure as well as the morphology with the bulk charge carrier mobility of the compounds. To this end, molecular dynamics (MD) simulations are performed yielding realistic equilibrated morphologies. Partial charges and molecular orbitals are calculated based on single molecules in vacuum using quantum chemical methods. The molecular orbitals are then mapped onto the molecular positions and orientations, which allows calculation of the transfer integrals between nearest neighbors using the molecular orbital overlap method. Thus we obtain realistic transfer integral distributions and their autocorrelations. In case of organic crystals the differences between two descriptions of charge transport, namely semi-classical dynamics (SCD) in the small polaron limit and kinetic Monte Carlo (KMC) based on Marcus rates, are studied. The liquid crystals are investigated solely in the hopping limit. To simulate the charge dynamics using KMC, the centers of mass of the molecules are mapped onto lattice sites and the transfer integrals are used to compute the hopping rates. In the small polaron limit, where the electronic wave function is spread over a limited number of neighboring molecules, the Schroedinger equation is solved numerically using a semi-classical approach. The results are compared for the different compounds and methods and, where available, with experimental data. The carbazole macrocycles form columnar structures arranged on a hexagonal lattice with side chains facing inwards, so columns can closely approach each other allowing inter-columnar and thus three-dimensional transport. When taking only intra-columnar transport into account, t.
Modelling Charge Transport For Organic Solar Cells Within Marcus Theory
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Author : Riccardo Volpi
language : en
Publisher: Linköping University Electronic Press
Release Date : 2016-12-20
Modelling Charge Transport For Organic Solar Cells Within Marcus Theory written by Riccardo Volpi and has been published by Linköping University Electronic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-12-20 with categories.
With the technological advancement of modern society, electronic devices are getting progressively more integrated in our everyday lives. Their continuouslygrowing presence is generating numerous concerns about costs, efficiency and the environmental impact of the electronic waste. In this context, organic electronics is finding its way through the market, allowing for potentially low-cost, light, flexible, transparent and environmentally friendly electronics. Despite the numerous successes of organic electronics, the functioning of several categories of organic devices still represents a technological challenge, due to problems like low efficiencies and stabilities (degradation over time). Organic devices are composed by one or more organic materials depending on the particular application. The conformation and electronic structure of the organic molecules as well as their supramolecular arrangement in the single phase or at the interface are known to strongly a affect the mobility and/or the efficiency of the device. While there is consensus on the fundamental physics of organic devices, we still lack a detailed comprehensive theory able to fully explain experimental data. In this thesis we focus on trying to expand our knowledge of charge transport in organic materials through theoretical modelling and simulation of organic electronic devices. While the methodology developed is generally valid for any organic device, we will particularly focus on the case represented by organic photovoltaics. The morphology of the system is obtained by molecular dynamics simulations. Marcus theory is used to calculate the hopping rate of the charge carriers and subsequently study the possibility of free charge carriers production in an organic solar cell. The theory is then compared both with Kinetic Monte Carlo simulations and with experiments to identify the main pitfalls of the actual theory and ways to improve it. The Marcus rate between two molecules depends on the molecular orbital energies, the transfer integral between the two molecules and the reorganization energy. The orbital energies and the transfer integrals between two neighbouring molecules are obtained through quantum mechanical calculations in vacuum. Electrostatic effects of the environment are included through atomic charges and atomic polarizabilities, producing a correction both to the orbital energy and to the reorganization energy. We have studied several systems in the single phase (polyphenylene vinylene, C60, PC61BM) and at the interface between two organic materials (anthracene/C60, TQ1/PC71BM). We show how a combination of different methodologies can be used to obtain a realistic ab-initio model of organic devices taking into account environmental effects. This allows us to obtain qualitative agreement with experimental data of mobility in the single phase and to determine whether or not two materials are suitable to be used together in an organic solar cell.
Switching Kinetics And Charge Transport In Organic Ferroelectrics
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Author : Tim Cornelissen
language : en
Publisher: Linköping University Electronic Press
Release Date : 2020-08-26
Switching Kinetics And Charge Transport In Organic Ferroelectrics written by Tim Cornelissen and has been published by Linköping University Electronic Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-08-26 with Electronic books categories.
The continued digitalization of our society means that more and more things are getting connected electronically. Since currently used inorganic electronics are not well suited for these new applications because of costs and environmental issues, organic electronics can play an important role here. These essentially plastic materials are cheap to produce and relatively easy to recycle. Unfortunately, their poor performance has so far hindered widespread application beyond displays. One key component of any electronic device is the memory. For organic electronics several technologies are being investigated that could serve as memories. One of these are the ferroelectrics, materials that have a spontaneous electrical polarization that can be reversed with an electric field. This bistable polarization which shows hysteresis makes these materials excellent candidates for use as memories. This thesis focuses on a specific type of organic ferroelectric, the supramolecular discotics. These materials consist of disk?like molecules that form columns in which all dipolar groups are aligned, giving a macroscopic ferroelectric polarization. Of particular interest are the benzenetricarboxamides (BTA), which are used as a model system for the whole class of discotic ferroelectrics. BTA uses a core?shell architecture which allows for easy modification of the molecular structure and thereby the ferroelectric properties. To gain a deeper understanding of the switching processes in this organic ferroelectric BTA, both microscopic and analytical modeling are used. This is supported by experimental data obtained through electrical characterization. The microscopic model reduces the material to a collection of dipoles and uses electrostatics to calculate the probability that these dipoles flip. These flipping rates are the input for a kinetic Monte Carlo simulation (kMC), which simulates the behavior of the dipoles over time. With this model we simulated three different switching processes on experimental time and length scales: hysteresis loops, spontaneous depolarization, and switching transients. The results of these simulations showed a good agreement with experiments and we can rationalize the obtained parameter dependencies in the framework of thermally activated nucleation limited switching (TA?NLS). The microscopic character of the model allows for a unique insight into the nucleation process of the polarization switching. We found that nucleation happens at different locations for field driven polarization switching as compared to spontaneous polarization switching. Field?driven nucleation happens at the contacts, whereas spontaneous depolarization starts at defects. This means that retention times in disordered ferroelectrics could be improved by reducing the disorder, without affecting the coercive field. Detailed analysis of the nucleation process also revealed a critical nucleation volume that decreases with applied field, which explains the Merz?like field?dependence of the switching time observed in experiments. In parallel to these microscopic simulations we developed an analytical framework based on the theory of TA?NLS. This framework is mainly focused on describing the switching transients of disordered ferroelectrics. It can be combined with concepts of the Preisach model, which considers a non?ideal ferroelectric as a collection of ideal hysterons. We were able to relate these hysterons and the distribution in their up? and down?switching fields to the microscopic structure of the material and use the combined models to explain experimentally observed dispersive switching kinetics. Whereas ferroelectrics on their own could potentially serve as memories, the readout of ferroelectric memories becomes easier if they are combined with semiconductors. We have introduced several molecular materials following the same design principle of a core?shell structure, which uniquely combine ferroelectricity and semiconductivity in one material. The experimental IV?curves of these materials could be described using an asymmetric Marcus hopping model and show their potential as memories. The combination of modeling and experimental work in this thesis thereby provides an increased understanding of organic ferroelectrics, which is crucial for their application as memories.
Monte Carlo Simulations Of Charge Transport In Organic Semiconductors
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Author : Pyie Phyo Aung
language : en
Publisher:
Release Date : 2014
Monte Carlo Simulations Of Charge Transport In Organic Semiconductors written by Pyie Phyo Aung and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014 with Charge transfer devices (Electronics) categories.
Thin film organic semiconductors have applications in electronic devices such as transistors, light emitting diodes, and organic solar cells. The performance of such devices depends on the mobility of the charge carriers which is strongly affected by the morphology of the material. In this work, we perform Monte Carlo simulations to study charge transport in lattice models of homogeneous and heterogeneous materials. The model device consists of a layer of the material between two electrodes at different potentials. Charge carriers are injected from the electrodes and move by hopping under the influence of the electric field and Coulomb interactions. To model the effect of polymer chain connectivity on charge transport we include an energetic barrier to hopping between sites on different chains. We measure current-voltage (I-V) characteristics of model devices and determine the mobility of the charge carriers from the slope of the I-V curves in the ohmic regime. We validate our algorithms with simulations of simple devices consisting of two parallel layers of donor and acceptor materials between the electrodes. To study the effect of ordered domains in polymeric semiconductors we simulate charge transport in a recently developed lattice model for polymers that undergo an order-disorder transition. We find that ordering in the material leads to strong anisotropies with increased mobility for transport parallel to the ordered domains and reduced mobility for perpendicular transport.
Charge Dynamics In Organic Semiconductors
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Author : Pascal Kordt
language : en
Publisher: Walter de Gruyter GmbH & Co KG
Release Date : 2016-09-12
Charge Dynamics In Organic Semiconductors written by Pascal Kordt and has been published by Walter de Gruyter GmbH & Co KG this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-09-12 with Science categories.
In the field of organic semiconductors researchers and manufacturers are faced with a wide range of potential molecules. This work presents concepts for simulation-based predictions of material characteristics starting from chemical stuctures. The focus lies on charge transport – be it in microscopic models of amorphous morphologies, lattice models or large-scale device models. An extensive introductory review, which also includes experimental techniques, makes this work interesting for a broad readership. Contents: Organic Semiconductor Devices Experimental Techniques Charge Dynamics at Dierent Scales Computational Methods Energetics and Dispersive Transport Correlated Energetic Landscapes Microscopic, Stochastic and Device Simulations Parametrization of Lattice Models Drift–Diusion with Microscopic Link
Charge Transport Simulations For Organic Electronics
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Author :
language : en
Publisher:
Release Date : 2015
Charge Transport Simulations For Organic Electronics written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2015 with categories.
Molecular Dynamics And Charge Transport In Organic Semiconductors
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Author :
language : en
Publisher:
Release Date : 2017
Molecular Dynamics And Charge Transport In Organic Semiconductors written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. Here we propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower than most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. In conclusion, much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.
Advances In Physical Organic Chemistry
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Author :
language : en
Publisher: Elsevier
Release Date : 1999-05-19
Advances In Physical Organic Chemistry written by and has been published by Elsevier this book supported file pdf, txt, epub, kindle and other format this book has been release on 1999-05-19 with Science categories.
Volume 32 is proof again of the platform provided by Advances in Physical Organic Chemistry for some of the most interesting and diverse papers being produced today. Contributions by academic and industrial chemists give the volume a perspective useful to those working in both fields.
Charge Carrier Transport In Amorphous Organic Semiconductors
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Author : Benjie Limketkai
language : en
Publisher:
Release Date : 2008
Charge Carrier Transport In Amorphous Organic Semiconductors written by Benjie Limketkai and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
(Cont) Most significantly, the theory will enable predictive models of organic semiconductor devices based on physical material parameters that may be determined by experimental measurements or quantum chemical simulations. Understanding charge transport and injection through these materials is crucial to enable the rational design for organic device applications, and also contributes to the general knowledge of the physics of materials characterized by charge localization and energetic disorder.