A Stepwise Melting‐Polymerizing Molecule for Hydrophobic Grain‐Scale Encapsulated Perovskite Solar Cell

Abstract Despite the ongoing increase in the efficiency of perovskite solar cells, the stability issues of perovskite have been a significant hindrance to its commercialization. In response to this challenge, a stepwise melting‐polymerizing molecule (SMPM) is designed as an additive into FAPbI 3 perovskite. SMPM undergoes a three‐stage phase transition during the perovskite annealing process: initially melting from solid to liquid state, followed by overflowing grain boundaries, and finally self‐polymerizing to form a hydrophobic grain‐scale encapsulation in perovskite solar cells, providing protection against humidity‐induced degradation. With this unique property, coupled with the advantages of improved crystallization, diminished non‐radiative recombination, and energy level alignment, FAPbI 3 ‐based perovskite solar cells with a 25.21% (small‐area) and 22.94% (1 cm 2 ) power conversion efficiency and over 2000 h T95% stability under 85% relative humidity is achieved. Furthermore, the SMPM‐based perovskite solar cells without external encapsulations sustain impressive stability during underwater operation, in which the black FAPbI 3 phase is maintained and Pb‐leakage is also effectively suppressed. Therefore, the SMPM strategy can offer a sustainable settlement in both stability and environmental issues for the commercialization of perovskite solar cells.