New insight into the ultra-long lifetime of excitons in organic–inorganic perovskite: Reverse intersystem crossing

Abstract

Recently, an effective exciton diffusion length L exceeding 100 μm has been reported for organic–inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing (RISC) from the triplet to the singlet state can enhance the quantum yield of photoluminescence greatly. In this study, our theoretical investigation indicated that the energy difference ΔEst between the singlet state and the triplet state of CH3NH3PbI3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic–inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.