The critical role of temperature-dependent mobilities in determining the open-circuit voltage of bulk-heterojunction organic solar cells

Abstract

While solution-processed bulk-heterojunction organic solar cells (OSCs) continue to attract attention as their efficiencies approach 20%, the physical origin of the non-radiative energy loss in OSCs remains under debate. Understanding the temperature dependence of open-circuit voltage (VOC) is thus important because it provides unique insights into the origin of energy loss. Herein, we simulate the VOC vs. T relation of PTB7-Th:PC71BM bulk-heterojunction OSCs within the range of 160–295 K by incorporating experimentally measured temperature-dependent mobilities into the drift-diffusion model, assuming bimolecular recombination as the primary recombination mechanism. Significantly, we find that the temperature dependence of VOC can only be correctly reproduced by the model when the temperature dependence of the carrier mobilities is taken into account. The effect of the Langevin reduction coefficient on the temperature dependence of VOC is also investigated.