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The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors pp 105–125Cite as

Charge Transfer States at Donor–Acceptor Heterojunctions

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Abstract

Organic solar cells rely on the conversion of a Frenkel exciton into free charges via a charge transfer state formed on a molecular donor-acceptor pair. These charge transfer states are strongly bound by Coulomb interactions, and yet efficiently converted into charge-separated states. In this chapter, we show how long-range molecular order and interfacial mixing generate homogeneous electrostatic forces that can drive charge separation and prevent minority-carrier trapping across a donor-acceptor interphase. Comparing a variety of small-molecule donor-fullerene combinations, we illustrate how tuning of molecular orientation and interfacial mixing leads to a tradeoff between photovoltaic gap and charge-splitting and detrapping forces, with consequences for the design of efficient photovoltaic devices. Drawing from both simulation and experimental results, we also investigate the empirical relationship between the temperature- and charge-density-dependent open-circuit voltage and charge transfer state energy.

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Authors and Affiliations

  1. Department of Chemistry, University of Cambridge, Cambridge, UK

    Carl R. Poelking

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Correspondence to Carl R. Poelking .

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Poelking, C.R. (2018). Charge Transfer States at Donor–Acceptor Heterojunctions. In: The (Non-)Local Density of States of Electronic Excitations in Organic Semiconductors. Springer Theses. Springer, Cham. https://doi.org/10.1007/978-3-319-69599-0_6

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