Position-locking of volatile reaction products by atmosphere and capping layers slows down photodecomposition of methylammonium lead triiodide perovskite.

The remarkable progress of metal halide perovskites in photovoltaics has led to the power conversion efficiency approaching 26%. However, practical applications of perovskite-based solar cells are challenged by the stability issues, of which the most critical one is photo-induced degradation. Bare CHNHPbI perovskite films are known to decompose rapidly, with methylammonium and iodine as volatile species and residual solid PbI and metallic Pb, under vacuum under white light illumination, on the timescale of minutes.