Steric control of the donor/acceptor interface: Implications in organic photovoltaic charge generation
AuthorsHolcombe, Thomas W.
Norton, Joseph E.
Goris, Ludwig J.
Brédas, Jean Luc
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AbstractThe performance of organic photovoltaic (OPV) devices is currently limited by modest short-circuit current densities. Approaches toward improving this output parameter may provide new avenues to advance OPV technologies and the basic science of charge transfer in organic semiconductors. This work highlights how steric control of the charge separation interface can be effectively tuned in OPV devices. By introducing an octylphenyl substituent onto the investigated polymer backbones, the thermally relaxed charge-transfer state, and potentially excited charge-transfer states, can be raised in energy. This decreases the barrier to charge separation and results in increased photocurrent generation. This finding is of particular significance for nonfullerene OPVs, which have many potential advantages such as tunable energy levels and spectral breadth, but are prone to poor exciton separation efficiencies. Computational, spectroscopic, and synthetic methods were combined to develop a structure-property relationship that correlates polymer substituents with charge-transfer state energies and, ultimately, device efficiencies. © 2011 American Chemical Society.
SponsorsThis work was supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), supported by King Abdullah University of Science and Technology (KAUST), and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 (synthesis and some device characterization work). T.W.H., C.H.W., and J.R. thank the National Science Foundation for graduate research fellowships. We gratefully acknowledge Polyera Inc. and Paul Armstrong for providing the Active Ink N2200 and PDL respectively, used in this study. Paul Armstrong and Yoshi Miyamoto are thanked for assistance with device optimization. We also thank David Kavulak and Barry Thompson for helpful discussions.
PublisherAmerican Chemical Society (ACS)