Excess PbI2 evolution for triple-cation based perovskite solar cells with 21.9% efficiency

The triple cation mixed perovskites (CsFAMA) are known as one of the most efficient candidates for perovskite solar cells (PSCs). It is found that the power conversion efficiency (PCE) of triple-cation based devices would increase with the test time extending, and the maximum efficiency is normally obtained after several days aging storage. Here, the relationship between enhanced device performance, excess PbI 2 and its evolution in triple cation perovskite films of initial days was systematically explored. The CsFAMA-PSCs are prepared by two-step methods under two environmental conditions, including in the glove box and the ambient air (30% humidity). After 7 days testing, the maximum PCE of PSCs under two conditions dramatically increased 12.4% and 12.2%, reached 21.68% and 21.89%, respectively. At initial days, the XRD peak intensities of perovskite phase gradually decreased and those corresponding to PbI 2 increased. Along with time-resolved photoluminescence (TRPL) and kelvin probe force microscopy (KPFM), it was found that the defects were passivated with the evolution of PbI 2 . This work reveals the excess PbI 2 and its evolution in perovskite film, which can further supplement the understanding of PbI 2 defect passivation.