Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

FAPbI(3) (FA(+) = formamidinium) perovskite, one of the most efficient basic components in nowadays perovskite solar cells (PCSs), undergoes spontaneous phase transition whilemolecular-level investigations are still lacking. Here, we report a structural study on the phase transition process of the FA-based perovskites based on isolation and identification of a series of single crystal intermediates. A key intermediate of 8H phase with unique structure is discovered, which helps elucidate the complete phase evolution and stabilization mechanism of FA-based perovskites. Our new insight based on the Pauling's rules not only deepens the understanding of the phase stabilization roles of cations and anions in maximizing the concentrations of corner-sharing halogens and cubic cages but also forms suggestion for fabrication of high-performance and long-term stable PCSs by controlling the factors such as composition, precursor solution, stoichiometry, and additives.

Automated summary

This study investigates the phase transition process of FA-based perovskites and identifies a key intermediate, providing insights into the phase evolution and stabilization mechanism. The findings deepen the understanding of the roles of cations and anions in maximizing halogen and cage concentrations, and offer suggestions for fabricating high-performance and stable PCSs by controlling various factors.