Stability of Tin- versus Lead-Halide Perovskites: Ab Initio Molecular Dynamics Simulations of Perovskite/Water Interfaces

Tin-halide perovskites (THPs) have emerged as promising lead-free perovskites for photovoltaics and photocatalysis applications but still fall short in terms of stability and efficiency with respect to their lead-based counterpart. A detailed understanding of the degradation mechanism of THPs in a water environment is missing. This Letter presents ab initio molecular dynamics (AIMD) simulations to unravel atomistic details of THP/water interfaces comparing methylammonium tin iodide, MASnI(3), with the lead-based MAPbI(3). Our results reveal facile solvation of surface tin-iodine bonds in MASnI(3), while MAPbI(3) remains more robust to degradation despite a larger amount of adsorbed water molecules. Additional AIMD simulations on dimethylammonium tin bromide, DMASnBr(3), investigate the origins of their unprecedented water stability. Our results indicate the presence of amorphous surface layers of hydrated zero-dimensional SnBr3 complexes which may protect the inner structure from degradation and explain their success as photocatalysts. We believe that the atomistic details of the mechanisms affecting THP (in)stability may inspire new strategies to stabilize THPs.

Automated summary

This study investigates the degradation mechanism and stability of tin-halide perovskites (THPs) in a water environment. The results show that THPs are more susceptible to dissolution in water compared to lead-based perovskites. Additionally, the study reveals that the success of THPs as photocatalysts can be attributed to the presence of hydrated amorphous surface layers that protect the inner structure from degradation.