Spatial Distribution of Lead Iodide and Local Passivation on Organo-Lead Halide Perovskite

We identify nanoscale spatial distribution of PbI₂ on the (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskite thin film and investigate the local passivation effect using confocal based optical microscopy of steady state and time-resolved photoluminescence (PL). Different from a typical scanning electron microscope (SEM) morphology study, confocal based PL spectroscopy and microscopy allow researchers to map the morphologies of both perovskite and PbI₂ grains simultaneously, by selectively detecting their characteristic fluorescent bands using band-pass filters. In this work, we compare the perovskite samples without and with excess PbI₂ incorporation and unambiguously reveal PbI₂ distribution for the PbI₂-rich sample. In addition, using the nanoscale time-resolved PL technique we show that the PbI₂-rich regions exhibit longer lifetime due to suppressed defect trapping, compared to the PbI₂-poor regions. The measurement on the PbI₂-rich sample indicates that the passivation effect of PbI₂ in perovskite film is effective, especially in localized regions. Hence, this finding is important for further improvement of the solar cells by considering the strategy of excess PbI₂ incorporation.