Analyzing the Light-Intensity Dependent Short-Circuit Current of Organic Solar Cells
Paula Hartnagel a, Thomas Kirchartz a b
a IEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, Germany, 52425 Jülich, Germany
b Faculty of Engineering and CENIDE, University of Duisburg-Essen, Germany
Online Conference
Proceedings of NFA-Based Organic Solar Cells: Materials, Morphology and Fundamentals (NFASC)
Online, Spain, 2021 February 3rd - 4th
Organizers: Natalie Banerji and Feng Gao
Oral, Paula Hartnagel, presentation 004
DOI: https://doi.org/10.29363/nanoge.nfasc.2021.004
Publication date: 25th January 2021

The rapid development of new organic solar cell material systems creates the need for quick and easy characterization of the major loss mechanisms. A key factor limiting the performance of organic solar cells is bimolecular recombination,[1, 2] which is frequently characterized by light-intensity dependent measurements of the short-circuit current.[3-5] The analysis is based on a zero-dimensional model, which predicts a sublinear relation between the light intensity and the short-circuit current in the presence of bimolecular recombination as opposed to the strictly linear relation in the ideal case or for non-geminate, monomolecular recombination. While previous works have already discussed that a linear correlation can also be compatible with substantial amounts of bimolecular, direct recombination,[2, 6] we go further beyond the zero-dimensional approximation. Here, we present the analysis of the influence of direct recombination and trap-assisted recombination via deep defect states and exponential band tails on the light-intensity dependence of the short-circuit current with numerical drift-diffusion simulations. The simulations reveal that a sublinear relation can occur for both direct and trap-assisted recombination caused by spatial redistribution of charge carriers, light-intensity dependent trapped charge-carrier densities and, in the case of thick devices, by space-charge effects.[7] Some of these cases cannot be explained by a simple, zero-dimensional device model and therefore highlight the need to understand the microscopic effects to correctly interpret the light-intensity dependent short-circuit current measurements.

T.K. and P.H. acknowledge funding by the Helmholtz Association.

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