Optimum mobility, contact properties, and open-circuit voltage of organic solar cells: A drift-diffusion simulation study

Abstract

evident from a decrease of the open-circuit voltage (Voc) with an increased role of charge carrier diffusion, which originates from a higher mobility or from interface barriers reducing the built-in potential. In this case, Voc furthermore depends on the device thickness. Considering the effect of different recombination models, a too high mobility of one charge carrier decreases Voc significantly for Langevin recombination. That is why balanced mobilities are desirable for high efficiency in this case. In presence of recombination via CT states, Voc is mainly governed by the dynamics of the charge transfer state. Based on these differentiations we show that the existence of an optimum mobility derived from simulation depends strongly on the assumptions made for contact and recombination properties and obtain a comprehensive picture how charge carrier mobility influences the parameters of organic solar cells.