Mixed-Halide CH3NH3PbI3−xXx (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, CH3NH3PbX3 (X=Cl, Br, I), by means of vapor‐assisted solution processing. Herein, the successful formation of mixed‐halide perovskites (CH3NH3PbI3−xXx) by means of a vapor‐assisted solution method at ambient atmosphere is reported. The perovskite films are synthesized by exposing PbI2 film to CH3NH3X (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 CH3NH3PbI3−xClx, the optimum reaction temperature is reduced to 100 °C, and the resulting phases are CH3NH3PbI3 (with trace Cl) and CH3NH3PbCl3 with a ratio of about 2:1. In the case of CH3NH3PbI3−xBrx, single‐phase CH3NH3PbI2Br is formed in a considerably shorter reaction time than that of CH3NH3PbI3. The mesostructured perovskite solar cells based on CH3NH3PbI3 films show the best optimal power conversion efficiency of 13.5 %, whereas for CH3NH3PbI3−xClx and CH3NH3PbI3−xBrx the best recorded efficiencies are 11.6 and 10.5 %, respectively. In a puff of gas: Perovskite films are synthesized by exposing PbI2 film to CH3NH3X (X=I, Br or Cl) vapor. Inclusion of Cl or Br into the structure leads to smaller grains and lower surface roughness (see figure). An efficiency of 13 % can be achieved by a solar cell fabricated with CH3NH3PbI3 outside the glove box under ambient conditions. The efficiency is lower for CH3NH3PbI3−xClx (11 %) and CH3NH3PbI3−xBrx (10 %), whereas the VOC values are larger for these devices.