Charge Transport in Self-Assembled Semiconducting Organic Layers: Role of Dynamic and Static Disorder

Vehoff, Thorsten; Chung, Yeon Sook; Johnston, Karen; Troisi, Alessandro; Yoon, Do Y.; Andrienko, Denis

doi:10.1021/jp101738g

Cited by 50 publications

(62 citation statements)

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“…In cases where a molecular translation or rotation during a simulation creates/ eliminates a connection between molecules, averaging over the entire simulation time will overestimate the connectivity of the charge transport network. We note that previous works have observed an increase in the average mobility upon time-averaging couplings, (10,27,29) which may point to this effect.…”

Section: Discussionsupporting

confidence: 64%

“…Work in this group and others has proposed a view of charge transport based in network analysis (5)(6)(7)(8)(9)(10). Network analysis represents a powerful means of analyzing structurally disordered charge transport networks, with the unique ability to place different mechanisms of charge transport on the same footing via the selection of a suitable graph metric.…”

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confidence: 99%

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Charge transport network dynamics in molecular aggregates

Jackson

Chen

Ratner

2016

Proc. Natl. Acad. Sci. U.S.A.

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Due to the nonperiodic nature of charge transport in disordered systems, generating insight into static charge transport networks, as well as analyzing the network dynamics, can be challenging. Here, we apply time-dependent network analysis to scrutinize the charge transport networks of two representative molecular semiconductors: a rigid n-type molecule, perylenediimide, and a flexible p-type molecule, bBDT(TDPP) 2 . Simulations reveal the relevant timescale for local transfer integral decorrelation to be ∼ 100 fs, which is shown to be faster than that of a crystalline morphology of the same molecule. Using a simple graph metric, global network changes are observed over timescales competitive with charge carrier lifetimes. These insights demonstrate that static charge transport networks are qualitatively inadequate, whereas average networks often overestimate network connectivity. Finally, a simple methodology for tracking dynamic charge transport properties is proposed.organic semiconductors | charge transport | network analysis | dynamic disorder | molecular semiconductors C omputational tools using periodic boundary conditions are integral to understanding charge and excitation transport in crystalline semiconducting materials (1, 2). In noncrystalline systems, where Bloch's theorem is inapplicable and inclusion of structural disorder is required for an accurate description of charge transport, comparable computational strategies are rare. Typically, one uses an approximate solution of the master equation with semiclassical rates derived from a combination of atomistic molecular dynamics (MD) and quantum chemistry. While this strategy has proven effective (3, 4), it possesses obvious deficiencies: it lacks both an explicit inclusion of structural dynamics and an understanding of the topology of charge transport networks.Work in this group and others has proposed a view of charge transport based in network analysis (5-10). Network analysis represents a powerful means of analyzing structurally disordered charge transport networks, with the unique ability to place different mechanisms of charge transport on the same footing via the selection of a suitable graph metric. Recently, network views of charge transport in structurally disordered systems have provided useful insights: notably, the relationship between a molecule's topology and the percolation threshold of its charge transport networks (5, 6), and that charge mobility can be independent of the global morphology, being primarily determined by local molecular packing (7).Although a useful framework, previous applications of network analysis to structurally disordered charge transport networks have neglected the role of dynamic structural disorder: static snapshots of the charge transport network were used for the network analysis. Transport was assumed to occur on a charge transport network defined by time-independent site energies and electronic couplings. Whereas the static picture provides many insights into the nature of charge transport in soft mater...

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Section: Discussionsupporting

confidence: 64%

mentioning

confidence: 99%

Charge transport network dynamics in molecular aggregates

Jackson

Chen

Ratner

2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Because of the structural complexity of organic semiconductors, the theoretical study of their charge transport properties is also quite challenging, so that theoretical studies are usually limited to structurally ordered systems. [9][10][11][12] A key electronic device based on the Zener effect, the Zener diode, is crucial for basic electrical circuit requirements, such as voltage-and temperature stabilization and overvoltage protection. An organic Zener diode with an adjustable breakdown is still missing.…”

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confidence: 99%

Organic Zener Diodes: Tunneling across the Gap in Organic Semiconductor Materials

Kleemann

Gutiérrez²,

Lindner

et al. 2010

Nano Lett.

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Organic Zener diodes with a precisely adjustable reverse breakdown from -3 to -15 V without any influence on the forward current-voltage curve are realized. This is accomplished by controlling the width of the charge depletion zone in a pin-diode with an accuracy of one nanometer independently of the doping concentration and the thickness of the intrinsic layer. The breakdown effect with its exponential current voltage behavior and a weak temperature dependence is explained by a tunneling mechanism across the highest occupied molecular orbital-lowest unoccupied molecular orbital gap of neighboring molecules. The experimental data are confirmed by a minimal Hamiltonian model approach, including coherent tunneling and incoherent hopping processes as possible charge transport pathways through the effective device region.

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“…and within the molecular building blocks -different from most "hard" matter, where the extended conjugated network in inorganic semiconductors or long-range metallic binding in metals prevent any such distinction. For the problem of charge transport in organic materials, the weak intermolecular coupling implies that nuclear and electronic degrees of freedom can (to some approximation [47][48][49]) be decoupled in a small-polaron way: Intramolecular nuclear/vibrational degrees of freedom are then included effectively in an appropriately chosen rate expression for charge or energy transfer, such as the semi-classical Marcus rate. Molecular diffusion, on the other hand, can be entirely disentangled from the dynamics of electronic states.…”

Section: The Bottom-up Simulation Workflowmentioning

confidence: 99%

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

Poelking

2018

Springer Theses

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The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors The rational design of organic semiconductors for optoelectronic devices relies on a detailed understanding of how their molecular and morphological structure condition the energetics and dynamics of charged and excitonic states. Investigating the role of molecular architecture, conformation, orientation and packing, this work reveals mechanisms that shape the spatially resolved densities of states in organic, small-molecular and polymeric heterostructures and mesophases. The underlying computational framework combines multiscale simulations of the material morphology at atomistic and coarse-grained resolution with a long-range-polarized embedding technique to resolve the electronic structure of the molecular solid. We show that longrange electrostatic interactions tie the energetics of microscopic states to the mesoscopic structure, with a qualitative and quantitative impact on charge-carrier level profiles across organic interfaces. The computational approach provides quantitative access to the charge-density-dependent opencircuit voltage of planar heterojunctions. The derived and experimentally verified relationships between molecular orientation, architecture, level profiles and open-circuit voltage rationalize the acceptor-donor-acceptor pattern for donor materials in high-performing solar cells. Proposing a pathway for barrier-less dissociation of charge transfer states, we highlight how mesoscale fields generate charge splitting and detrapping forces in systems with finite interface roughness. The associated design rules reflect the dominant role played by lowest-energy configurations at the interface. Acknowledgements 121 Die (nicht-)lokale Zustandsdichte elektronischer Anregungen in organischen Halbleitern List of Publications 123Bibliography 125 Chapter 1 Organic Electronics in a NutshellThe discovery of conductive polymers in the 1970s [1,2] -rewarded with the Nobel prize in chemistry in the year 2000 -and subsequent development of the first polymeric electronic devices in the 1980s [3-5] have marked the beginnings of a vast interdisciplinary research field referred to as organic electronics. Drawing from both polymeric and small-molecular semiconductors, organic thin-film transistors, solar cells, light-emitting diodes, photodetectors and sensors name just a few out of many applications that make use of the supreme chemical versatility and mechanical flexibility of the underlying "soft" molecular materials. Furthermore enabling low-temperature solution-based processing, printing and spray coating, organic electronics is set to complement the conventional silicon-based electronics in diverse waysadding functionality and improving sustainability. This introductory chapter will provide a short review of the materials and device physics, as well as of new trends and challenges that emerged in the field over the past decade. MaterialsOrganic semiconductors are molecular materials that exist at the interface between orga...

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Charge Transport in Self-Assembled Semiconducting Organic Layers: Role of Dynamic and Static Disorder

Cited by 50 publications

References 54 publications

Charge transport network dynamics in molecular aggregates

Charge transport network dynamics in molecular aggregates

Organic Zener Diodes: Tunneling across the Gap in Organic Semiconductor Materials

The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors

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