High Performance Inverted RbCsFAPbI₃ Perovskite Solar Cells Based on Interface Engineering and Defects Passivation

Lead halide‐based perovskites solar cells (PSCs) are intriguing candidates for photovoltaic technology due to their high efficiency, low cost, and simple fabrication processes. Currently, PSCs with efficiencies of >25% are mainly based on methylammonium (MA)‐free and bromide (Br) free, formamide lead iodide (FAPbI₃)‐based perovskites, because MA is thermally unstable due to its volatile nature and Br incorporation will induce blue shift in the absorption spectrum. Therefore, MA‐free, Br‐free formamidine‐based perovskites are drawing huge research attention in recent years. The hole transporting layer (HTL) is crucial in fabricating highly efficient and stable inverted p‐i‐n structured PSCs by enhancing charge extraction, lowering interfacial recombination, and altering band alignment, etc. Here, this work employs a NiO_x/PTAA bi‐layer HTL combined with GuHCl (guanidinium hydrochloride) additive engineering and PEAI (phenylethylammonium iodide) passivation strategy to optimize the charge carrier dynamics and tune defects chemistry in the MA‐free, Br‐free RbCsFAPbI₃‐based perovskite absorber, which boosts the device efficiency up to 22.78%. Additionally, the device retains 95% of its initial performance under continuous 1 sun equivalent LED light illumination at 45 °C for up to 500 h.