Extra long electron–hole diffusion lengths in CH3NH3PbI3−xClx perovskite single crystals

Abstract

Long electron–hole diffusion lengths in organolead trihalide compounds play a key role in achieving the remarkable performance of perovskite photovoltaics. Diffusion lengths in solution-grown CH₃NH₃PbI₃ single crystals have been found to be greater than 175 micrometer (μm). Herein, we report the diffusion lengths in CH₃NH₃PbI_3−xCl_x single crystals exceeding 380 μm under 1 Sun illumination, which is twice that in CH₃NH₃PbI₃ single crystals. Incorporation of chlorine is found to increase the density of trap-states and reduce the valence band level; these two factors, which dominate the carrier recombination and the charge transfer, respectively, are in a competing relation. As a result, the electron–hole diffusion lengths in a CH₃NH₃PbI_3−xCl_x single crystal with an optimum Cl proportion (x = 0.005) reach the maximum values. This study provides a strategy for the design of perovskite optoelectronics.