Nematic Ordering, Conjugation, and Density of States of Soluble Polymeric Semiconductors

Gemünden, Patrick; Poelking, Carl; Kremer, Kurt; Andrienko, Denis; Daoulas, Kostas Ch.

doi:10.1021/ma400646a

Cited by 60 publications

(142 citation statements)

References 106 publications

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“…The model and backmapping scheme were developed by P. Gemünden and K. Daoulas [72]: Within the model, particles represent entire repeat units of the polymer, including side chains. The local frame of these particles is given by the righthanded trihedron {u, v, w}, where u points along the backbone, w along the normal of the conjugated π-plane, and v = w × u. Bonded interactions are derived systematically in a bottom-up manner from a Boltzmann inversion of the atomistic conformational distribution functions.…”

Section: Coarse-grained Modelsmentioning

confidence: 99%

“…The phenomenological potential thus mimics the π-π interaction between conjugated subunits. Realistic values for ν and λ can be derived from the mechanical properties of the polymer, and are on the order of several k B T [72,73]. By tuning their relative strengths, it is furthermore possible to simulate amorphous, nematic and biaxial systems within the same framework.…”

Section: Coarse-grained Modelsmentioning

confidence: 99%

“…The latter can be achieved via linear scaling methods such as the tight-binding approximation of DFT (DFTB) [84,85]. A computationally less demanding, but crude [86] approach is to employ a heuristic criterion for conjugation [71,72]: Polymer chains are then partitioned onto their units of transport based on a cutoff criterion for the torsional deviation from the planar cis-and trans-conformations of two successive repeat units.…”

Section: System Partitioningmentioning

confidence: 99%

Section: The Mesoscopic Interaction Rangementioning

confidence: 99%

“…As a quantitative treatment usually requires an atomistic resolution, system sizes addressed in today's simulations may in particular prove insufficient to sample the tail of the densities of states, which determines the charge-carrier mobility. Possible solutions to some of these finite-size effects include statistical extrapolation techniques [28] or coarse-grained descriptions with reinsertion of atomistic details [72].Still, the need to go beyond the local molecular ordering associated with a length scale of some nanometers is not only due to sampling requirements: It is additionally motivated by the fact that organic semiconductors are made of quadrupolar building blocks [104,105], which give rise to an uncompensated quadrupole moment that in ordered systems extends to the mesoscale and beyond. For computations, this complicates matters, as the interaction of a charge with a 3D-periodic net-quadrupolar environment is only conditionally convergent [106].…”

mentioning

confidence: 99%

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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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Section: Coarse-grained Modelsmentioning

confidence: 99%

Section: Coarse-grained Modelsmentioning

confidence: 99%

Section: System Partitioningmentioning

confidence: 99%

Section: The Mesoscopic Interaction Rangementioning

confidence: 99%

mentioning

confidence: 99%

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

Poelking

2018

Springer Theses

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Correlating Ultrafast Dynamics, Liquid Crystalline Phases, and Ambipolar Transport in Fluorinated Benzothiadiazole Dyes

Boehme

Yimga

Frick

et al. 2021

Adv Elect Materials

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organic semiconductors (OSCs) that can be easily processed with low-cost, largethroughput fabrication techniques. While high carrier mobilities are generally desirable, optoelectronic devices, such as organic light-emitting diodes [1] and organic photovoltaics, [2] specifically profit from ambipolar transport, i.e., balanced electron and hole transport. However, the majority of OSCs are predominantly unipolar, and demonstrate higher hole mobilities than electron mobilities. [3] Therefore, device fabrication typically requires the deposition of multiple unipolar OSCs to achieve the desired electrical properties, thereby complicating the fabrication protocols.Soluble small-molecule semiconductors that form crystalline films have the potential to combine the advantages of high chemical purity and superior (opto)electronic properties with good processability. However, crystalline organic films formed from soluble small molecules often display poor structural and thermal integrity, as well as lower carrier mobilities compared to nonsoluble small-molecule derivatives. In other words, processability generally comes at the expense of both reduced thermal and mechanical stability, as well as electrical transport.In this study, we synthesized soluble small-molecule dyes that form crystalline films at room temperature, but A key challenge in the field of organic electronics is predicting how chemical structure at the molecular scale determines nature and dynamics of excited states, as well as the macroscopic optoelectronic properties in thin film. Here, the donor-acceptor dyes 4,7-bis[5-[4-(3-ethylheptyl)-2,3-difluorophenyl]-2-thienyl]-2,1,3-benzothiadiazole (2,3-FFPTB) and 4,7-bis[5-[4-(3-ethylheptyl)-2,6-difluorophenyl]-2-thienyl]-2,1,3-benzothiadiazole (2,6-FFPTB) are synthesized, which only differ in the position of one fluorine substitution. It is observed that this variation in chemical structure does not influence the energetic position of the molecular frontier orbitals or the ultrafast dynamics on the FFPTB backbone.However, it does result in differences at the macroscale, specifically regarding structural and electrical properties of the FFPTB films. Both FFPTB molecules form crystalline films at room temperature, whereas 2,3-FFPTB has two ordered smectic phases at elevated temperatures, and 2,6-FFPTB does not display any liquid crystalline phases. It is demonstrated that the altered location of the fluorine substitution allows to control the electrostatic potential along the molecular backbone without impacting molecular energetics or ultrafast dynamics. Such a design strategy succeeds in controlling molecular interactions in liquid crystalline phase, and it is shown that the associated molecular order, or rather disorder, can be exploited to achieve ambipolar transport in FFPTB films.

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Effect of Mesoscale Ordering on the Density of States of Polymeric Semiconductors

Gemünden

Poelking

Kremer

et al. 2015

Macromol. Rapid Commun.

Self Cite

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A multiscale simulation scheme, which incorporates both long-range conformational disorder and local molecular ordering, is proposed for predicting large-scale morphologies and charge transport properties of polymeric semiconductors. Using poly(3-hexylthiophene) as an example, it is illustrated how the energy landscape and its spatial correlations evolve with increasing degree of structural order in mesophases with amorphous, uniaxial, and biaxial nematic ordering. It is shown that the formation of low-lying energy states in more ordered systems is mostly due to larger (on average) conjugation lengths and not due to electrostatic interactions. The proposed scheme is general and can be applied to a wide range of polymeric organic materials.

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Nematic Ordering, Conjugation, and Density of States of Soluble Polymeric Semiconductors

Cited by 60 publications

References 106 publications

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

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

Correlating Ultrafast Dynamics, Liquid Crystalline Phases, and Ambipolar Transport in Fluorinated Benzothiadiazole Dyes

Effect of Mesoscale Ordering on the Density of States of Polymeric Semiconductors

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