Methylamine vapor exposure for improved morphology and stability of cesium-methylammonium lead halide perovskite thin-films

Abstract

Mixed-cation cesium-methylammonium lead halide perovskite (CsxMA1 −xPbI3−xBrx) thin-films have been used to demonstrate stable and efficient perovskite devices. However, a systematic study of the Cs incorporation on the properties of the perovskite films has not been reported. In this report, impact of cesium incorporation on the minority carrier recombination lifetime of cesium-methylammonium lead halide perovskite thin-films is studied. The lifetime of the as-deposited perovskite films decreases with increasing concentration of cesium. However, mixed-cation perovskite films are more stable, showing higher lifetimes (15–20 µs) after 9 h of ambient exposure than just after deposition (6–13 µs). ‘Methylamine Vapor Exposure’ (MVE) technique was used to improve the morphology of the as-deposited film. MVE treated films are more oriented along (110) direction and were even more stable in ambient, with Cs0.10 MA0.90PbI2.90Br0.10 films showing lifetime of almost 50 ls after 9 h of ambient exposure, twice the lifetime of a comparable MAPbI3 film. These results throw light on why mixed-cation cesium-methylammonium lead halide perovskite films are better for highly efficient and stable perovskite solar cells.