Unraveling the Passivation Process of PbI 2 to Enhance the Efficiency of Planar Perovskite Solar Cells

There appears to be a controversy on whether remnant PbI 2 is beneficial to the performance of perovskite solar cells (PSCs). We have shown that PSCs with residual PbI 2 deposited by one-step antisolvent solution and two-step evaporation-solution method both have shown better performance than those without excess PbI 2 . X-ray diffraction with diverse X-ray incident angles combined with scanning electron microscopy and secondary-ion mass spectrometry is employed to identify the position of remnant PbI 2 . It reveals that residual PbI 2 is located at grain boundaries near the perovskite/hole-transporting layer interface area for the one-step antisolvent solution method, and the two-step evaporation-solution method situates the excess PbI 2 at grain boundaries and the electron transport layer/perovskite interface. The cell performance implies that grain boundary passivation is beneficial for promoting short-circuit current density, while interface passivation is more favorable to enhance open-circuit voltage and fill factor. The revealed passivation process indicates a deep understanding of remnant PbI 2 and contributes to the development of PSCs.