Reciprocal carrier collection in organic photovoltaics

Abstract
Buffer layers between the acceptor and cathode can perform several functions in organic photovoltaic devices, such as providing exciton blocking, protection of active layers against damage from cathode deposition, and optical spacing to maximize the electric field in the active device region. Here, we study electron collection by replacing the common buffer layer, bathocuproine, with a series of six, substituted tris(β-diketonato)Ru(III) analogues in the structure: indium-tin-oxide/copper phthalocyanine/C60/buffer/Ag. These buffer layers enable collection of photogenerated electrons by transporting holes from the cathode to the C60/buffer interface, followed by recombination with photogenerated electrons in the acceptor. We use a model for free-polaron and polaron-pair dynamics to describe device operation and the observed inflection in the current-voltage characteristics. The device characteristics are understood in terms of hole transfer from the highest occupied molecular orbital energy levels of several Ru-complexes to the acceptor. © 2011 American Physical Society.

Citation
Renshaw CK, Schlenker CW, Thompson ME, Forrest SR (2011) Reciprocal carrier collection in organic photovoltaics. Physical Review B 84. Available: http://dx.doi.org/10.1103/PhysRevB.84.045315.

Acknowledgements
This work was funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, through the Energy Frontier Research Centers: the Center for Energy Nanoscience at the University of Southern California (Award No. DE-SC0001013, materials synthesis, C.W.S.) and the Center for Solar and Thermal Energy Conversion in Complex Materials at the University of Michigan (Award No. DE-SC0000957, theoretical analysis, S.R.F.); the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST, C.W.S. and M.E.T.); the collaborative R&D program with technology advanced country (2009-advanced-B-015), by the Ministry of Knowledge and Economy of Korea between Dankook University and the University of Michigan (UPS measurements, C.K.R.); and by Global Photonic Energy Corporation (materials analysis, M.E.T. and S.R.F.).

Publisher
American Physical Society (APS)

Journal
Physical Review B

DOI
10.1103/PhysRevB.84.045315

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