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

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 (mm). Herein, we report the diffusion lengths in CH3NH3PbI3-xClx single crystals exceeding 380 mm 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 CH3NH3PbI3-xClx 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.