Compositional effect on water adsorption on metal halide perovskites

Highlights: • The adsorption of water on several metal halide perovskites are studied. • Density Functional Theory calculation and chemical bonding analysis are employed. • The compositional effect of perovskites on the water adsorption are elucidated. The moisture-induced instability of metal halide perovskites is one of the major challenges for perovskite devices. Although compositional engineering has been widely employed to improve the overall stability of perovskites, its effect on the moisture-induced instability received little attention. Here, we systematically study the interaction of water with the surfaces of primary perovskites, AMX₃ (A⁺ = MA⁺, FA⁺, Cs⁺; M²⁺ = Pb²⁺, Sn²⁺; X⁻ = I⁻, Br⁻), by using Density Functional Theory (DFT) calculations and comprehensive chemical bonding analysis. We reveal that the hydrophilic group NH₃⁺ of MA⁺ cation may be the cause for instability issues. We find that the adsorption of water on FAPbI₃ and CsPbI₃ are much weaker than on MAPbI₃ due to the less polarity of FA⁺ and Cs⁺. When exchanging M²⁺ cations, water adsorption on MASnI₃ is also less energetically favorable than on MAPbI₃ because of the weaker ionic interaction of H₂O-MASnI₃. When exchanging X⁻ anion, water adsorption on MAPbBr₃ is slightly weaker than on MAPbI₃ due to the slightly weaker covalent interaction of H₂O-MAPbBr₃. Our results present a comprehensive understanding of the compositional effect on the interactions of water with perovskites and provide rational design strategies to improve their stability against moisture via compositional engineering.