Influence of water intercalation and hydration on chemical decomposition and ion transport in methylammonium lead halide perovskites

TL;DR

This study uses first-principles calculations to analyze how water intercalation and hydration affect the decomposition and ion transport in methylammonium lead halide perovskites, revealing hydration's role in degradation.

Contribution

It provides a detailed mechanistic understanding of water's impact on perovskite stability and ion migration, highlighting the importance of avoiding hydration in PSCs.

Findings

Water exothermically intercalates into perovskites

Hydration reduces activation energies for ion migration

Hydrated compounds are thermodynamically stable

Abstract

The use of methylammonium (MA) lead halide perovskites \ce{CH3NH3PbX3} (X=I, Br, Cl) in perovskite solar cells (PSCs) has made great progress in performance efficiency during recent years. However, the rapid decomposition of \ce{MAPbI3} in humid environments hinders outdoor application of PSCs, and thus, a comprehensive understanding of the degradation mechanism is required. To do this, we investigate the effect of water intercalation and hydration of the decomposition and ion migration of \ce{CH3NH3PbX3} using first-principles calculations. We find that water interacts with \ce{PbX6} and MA through hydrogen bonding, and the former interaction enhances gradually, while the latter hardly changes when going from X=I to Br and to Cl. Thermodynamic calculations indicate that water exothermically intercalates into the perovskite, while the water intercalated and monohydrated compounds are stable with respect to decomposition. More importantly, the water intercalation greatly reduces the activation energies for vacancy-mediated ion migration, which become higher going from X=I to Br and to Cl. Our work indicates that hydration of halide perovskites must be avoided to prevent the degradation of PSCs upon moisture exposure.