Stable α‐FAPbI3 in Inverted Perovskite Solar Cells with Efficiency Exceeding 22% via a Self‐Passivation Strategy

Abstract Formamidinium lead iodide (FAPbI 3 ) has endowed power conversion efficiencies (PCEs) up to 25.5% in regular‐structured perovskite solar cells (PSCs) because of its optimal bandgap and enhanced thermal stability. However, the performance of FAPbI 3 ‐based inverted‐structured PSCs is unsatisfactory. Herein, four kinds of commonly used hole transport materials (HTMs) are selected, including PEDOT:PSS, PTAA, NiO x , and MeO‐2PACz, to study their impact on the methylamine chloride (MACl)‐assisted one‐step deposition of FAPbI 3 films. It is found that MeO‐2PACz is the optimal substrate for stabilizing black‐phase FAPbI 3 and the corresponding inverted‐structured PSCs show the best photovoltaic performance. Nonetheless, the PCE is restricted by low open‐circuit voltage ( V OC ) due to non‐radiative recombination caused by MACl residues. Therefore, homologous PbI 2 in situ passivation is implemented to passivate defects at grain boundaries. The addition of excess PbI 2 in precursor solution remarkably decreases charge trap densities and elongates carrier lifetimes. As a result, the optimized device achieves an impressive PCE of 22.13%, which is the highest efficiency of FAPbI 3 based on inverted‐structured PSCs. Moreover, the best device exhibits free hysteresis and excellent long‐term stability, maintaining 92% of the initial PCEs after 800 h aging under ambient conditions.