Light-modulated scanning tunneling microscopy studied on photoinduced carrier generations at PbI$_{2}$/perovskite interface of perovskite solar cells

Perovskite solar devices based on CH$_{3}$NH$_{3}$PbX$_{3}$ (X = Cl, Br, I) have recently shown tremendous efficiency enhancements up to 20\% in photovoltaic applications. The presence of PbI2 in perovskite films has been found to affect the charge carrier transport behaviors and device performance of perovskite solar cells. In this work, we employed the unique ability of light-modulated scanning tunneling microscopy (LM-STM) technique to dircetly reveal the correlation of the nanoscaled compositional distributions and photo-induced interfacial electronic structures at the PbI2/perovskite interface of perovskite grains under light illumination. The result reveals the important role of the optimum PbI$_{2}$ passivation layers (a thickness less than 20 nm) on the charge separation and recombination at perovskite crystal grains. The unique LM-STM technique demonstartes great potential for application in the future exploring photovoltaic systems.