Impact of mesoscale order on open-circuit voltage in organic solar cells

Poelking, Carl; Tietze, M Max; Elschner, Chris; Olthof, Selina; Hertel, Dirk; Baumeier, Björn; Würthner, Frank; Meerholz, Klaus; Leo, Karl; Andrienko, Denis

doi:10.1038/nmat4167

Cited by 200 publications

(231 citation statements)

References 49 publications

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“…D5M, by contrast, carries a sizeable negative long-axis quadrupole and a smaller positive out-of-plane component, as a result of its ADA structure. This distinctive quadrupolar layout has interesting implications for device operation [106], as will also become clear from the analysis in this section.…”

Section: Interplay Of Molecular Architecture Packing and Orientationmentioning

confidence: 80%

“…For computations, this complicates matters, as the interaction of a charge with a 3D-periodic net-quadrupolar environment is only conditionally convergent [106]. For 2D-periodic systems used to describe thin films, by contrast, the convergence of the interaction sum is absolute, but very slow.…”

Section: Chapter 3 the Local Density Of Statesmentioning

confidence: 99%

“…A rigorous evaluation of the thermally broadened density of states of donor and acceptor species as pursued in Chapter 4, by contrast, shows that calculation of the charge-densitydependent (as opposed to illumination-intensity-dependent) V oc is possible [106]. Regrettably, such an approach can still be misleading, as it imposes a finite steady-state charge density and hence does not verify whether charges are generated in the first place.…”

Section: Pathway For Charge Splitting and Detrappingmentioning

confidence: 99%

“…Similarly, neither entropydriven separation [136] nor long-range charge transfer [138] boost rates to an extent that justifies an ultrafast process. Continuous level bending has been proposed as a further pathway for cold-exciton break-up [97], but it would still lead to locally bound CT states, and, more importantly, will not necessarily hold in the presence of mesoscale order, which yields flat level profiles [106].…”

Section: Pathway For Charge Splitting and Detrappingmentioning

confidence: 99%

“…We saw previously that the interaction sum associated with a net charge embedded in a net-quadrupolar environment is in general only conditionally convergent [106,122]). In a thin-film setup, the 1/r 3 character of the charge-quadrupole interaction still results in a rather slow convergence, with the effect that the energetics is tied to the degree of mesoscale order.…”

Section: Dielectric Solvation Of Electron-hole Pairsmentioning

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: Interplay Of Molecular Architecture Packing and Orientationmentioning

confidence: 80%

Section: Chapter 3 the Local Density Of Statesmentioning

confidence: 99%

Section: Pathway For Charge Splitting and Detrappingmentioning

confidence: 99%

Section: Pathway For Charge Splitting and Detrappingmentioning

confidence: 99%

Section: Dielectric Solvation Of Electron-hole Pairsmentioning

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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Modeling of Organic Light Emitting Diodes: From Molecular to Device Properties

Kordt

Holst

Helwi

et al. 2015

Adv Funct Materials

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146

153

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The progress in modeling of charge transport in disordered organic semiconductors on various length scales, from atomistic to macroscopic, is reviewed. This includes evaluation of charge transfer rates from first principles, parametrization of coarse‐grained lattice and off‐lattice models, and solving the master and drift‐diffusion equations. Special attention is paid to linking the length scales and improving the efficiency of the methods. All techniques are illustrated on an amorphous organic semiconductor, DPBIC, a hole conductor and electron blocker used in state of the art organic light emitting diodes (OLEDs). The outlined multiscale scheme can be used to predict OLED properties without fitting parameters, starting from chemical structures of compounds.

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Why Inverted Small Molecule Solar Cells Outperform Their Noninverted Counterparts

Nanova

Scherer

Schell

et al. 2015

Adv Funct Materials

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It is shown that the effect of substrate heating on the photo conversion effi ciency in vacuum-deposited small molecule organic solar cells is closely related to the improved free charge generation in ordered C 60 regions. The formation of these ordered regions strongly depends on the deposition sequence in the device and differs therefore between inverted and noninverted cells. Substrate-induced local fullerene ordering is found in small molecule:C 60 bulk heterojunctions (BHJs) deposited on pristine C 60 at elevated temperatures. This does not occur for BHJs deposited under identical conditions on pristine donor molecule layers, despite similar degrees of phase separation in both cases. These fi ndings point to a hitherto unidentifi ed advantage of inverted over noninverted solar cells that manifests itself in a higher charge separation effi ciency.

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Impact of mesoscale order on open-circuit voltage in organic solar cells

Cited by 200 publications

References 49 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

Modeling of Organic Light Emitting Diodes: From Molecular to Device Properties

Why Inverted Small Molecule Solar Cells Outperform Their Noninverted Counterparts

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