We employ Kelvin-probe force microscopy (KPFM) and photoconductive-atomic force microscopy (pc-AFM) to comprehensively evaluate the nanoscale transformations in optoelectrical properties in multi-cation metal halide perovskites. We quantify the changes in photocurrent and photovoltage for both dual-cation and quad-cation perovskite. The superior electrical performance observed in quad-cation perovskite, lent by Rb+ cation, will be discussed in detail. An in-depth analysis of photoactivity within grains and grain boundaries will be shared. Further, a mechanism for charge carrier transport is proposed through two types of GBs- with defects, and with defect passivation in dual and quad-cation perovskite, respectively.
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