Suppressing the Precursor Aging for Efficient Formamidinium-Based Dion–Jacobson Two-Dimensional Perovskite Solar Cells

For the quasi-two-dimensional (Q-2D) perovskites containing formamidinium cations (FA+), the chemical reaction between FA+ and amine-based organic spacers deteriorates the phase purity and repeatability of perovskite solar cells (PSCs), but it has attracted little attention so far. In this work, the aging process of the 1,3-propanediamine- (PDA-) and FA+-based Dion-Jacobson (DJ) type Q-2D perovskite precursor has been investigated. The deprotonated PDA interacts with the FA+ via its two terminal amines successively to form a ring molecule, giving rise to a highly insoluble complex with lead iodide and causing reversible precursor aging. Adding a small amount of acid is demonstrated as a general route to eliminate the FA+-related reactions in the precursor. In our study, the used methanesulfonic acid (MSA) effectively eliminates the precursor aging in both PDA- and butylamine (BA)-containing Q-2D perovskite films and meanwhile passivates the undercoordinated Pb2+ with its S═O group, leading to both improved power conversion efficiency (PCE) of solar cells and precursor stability. FA-based Q-2D PSCs have been enhanced from 14.60% to 18.26%.