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

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 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-based perovskite solar cells with a 25.21% (small-area) and 22.94% (1 cm) 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 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.