[en] Impact of Cesium incorporation on the minority carrier recombination lifetime of Cesium-Methylammonium lead halide perovskite (Cs_xMA_(1-x)PbI_(3-x)Br_x) thin-films is studied for both the as-deposited and Methylammine vapor exposed (MVE) perovskite films. MVE films were seen to have better crystallinity, morphology and coverage in comparison to the as-deposited film. Although with increase in Cesium content the lifetime values fell down for both the as-deposited and MVE films but exposure to humidity enhanced the same. The lifetime values showed a sharp increase of 300% for 10% Cesium incorporated MVE films post ambient humidity exposure for 5-6 hours. We fabricated meso-structured mixed cation MVE perovskite devices and showed efficiency more than 17%. Further, stability test against moisture for fresh and aged perovskite films post device fabrication were also carried out. These results provide insight on why mixed-halide perovskite films are better for highly efficient and stable perovskite solar cells. (author)