Mixed‐Halide CH 3 NH 3 PbI 3− x X x (X=Cl, Br, I) Perovskites: Vapor‐Assisted Solution Deposition and Application as Solar Cell Absorbers

There have been recent reports on the formation of single‐halide perovskites, CH 3 NH 3 PbX 3 (X=Cl, Br, I), by means of vapor‐assisted solution processing. Herein, the successful formation of mixed‐halide perovskites (CH 3 NH 3 PbI 3− x X x ) by means of a vapor‐assisted solution method at ambient atmosphere is reported. The perovskite films are synthesized by exposing PbI 2 film to CH 3 NH 3 X (X=I, Br, or Cl) vapor. The prepared perovskite films have uniform surfaces with good coverage, as confirmed by SEM images. The inclusion of chlorine and bromine into the structure leads to a lower temperature and shorter reaction time for optimum perovskite film formation. In the case of CH 3 NH 3 PbI 3− x Cl x , the optimum reaction temperature is reduced to 100 °C, and the resulting phases are CH 3 NH 3 PbI 3 (with trace Cl) and CH 3 NH 3 PbCl 3 with a ratio of about 2:1. In the case of CH 3 NH 3 PbI 3− x Br x , single‐phase CH 3 NH 3 PbI 2 Br is formed in a considerably shorter reaction time than that of CH 3 NH 3 PbI 3 . The mesostructured perovskite solar cells based on CH 3 NH 3 PbI 3 films show the best optimal power conversion efficiency of 13.5 %, whereas for CH 3 NH 3 PbI 3− x Cl x and CH 3 NH 3 PbI 3− x Br x the best recorded efficiencies are 11.6 and 10.5 %, respectively.