Spatially Resolved Imaging on Photocarrier Generations and Band Alignments at Perovskite/PbI₂ Heterointerfaces of Perovskite Solar Cells by Light-Modulated Scanning Tunneling Microscopy

The presence of the PbI₂ passivation layers at perovskite crystal grains has been found to considerably affect the charge carrier transport behaviors and device performance of perovskite solar cells. This work demonstrates the application of a novel light-modulated scanning tunneling microscopy (LM-STM) technique to reveal the interfacial electronic structures at the heterointerfaces between CH₃NH₃PbI₃ perovskite crystals and PbI₂ passivation layers of individual perovskite grains under light illumination. Most importantly, this technique enabled the first observation of spatially resolved mapping images of photoinduced interfacial band bending of valence bands and conduction bands and the photogenerated electron and hole carriers at the heterointerfaces of perovskite crystal grains. By systematically exploring the interfacial electronic structures of individual perovskite grains, enhanced charge separation and reduced back recombination were observed when an optimal design of interfacial PbI₂ passivation layers consisting of a thickness less than 20 nm at perovskite crystal grains was applied.