Influence of the temperature on the charge transport and recombination profile in organic bulk heterojunction solar cells: a drift-diffusion study

Abstract

Charge transport and recombination in organic semiconductors in the presence of temperature have an important role in device efficiency. In this study, we investigated the influence of the temperature on the charge transport and charge carrier generation and recombination kinetics in bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM). By solving the drift diffusion and Poisson equations via finite element method , the effects of the temperature on characteristic parameters of the cell have been studied. Considering the effect of different recombination models such as Langevin, trap-assisted and geminate recombinations, at low temperature of cell a reduction in the recombination rate observed, and therefore, open-circuit voltage ( $$V_{\mathrm{{oc}}}$$ ) increased by decreasing the temperature. Langevin recombination is a dominating factor in total recombination which geminate recombination has very little impact on the total recombination rate. It was shown that $$V_{\mathrm{{oc}}}$$ is mainly governed by the dynamics of the charge transfer state and it significantly affected by carrier recombination profile. Detail study of the exciton profile and influences on the $$V_{\mathrm{{oc}}}$$ will allow for a more efficient donor/acceptor cell design, which can be led to improve photovoltaic performance. Calculated $$J$$ – $$V$$ characteristics and temperature dependence of $$V_{\mathrm{{oc}}}$$ reveal relatively good agreement between the model’s predictions and published modeling and experimental reports.