Vacuum co-deposited CH3NH3PbI3 films by controlling vapor pressure for efficient planar perovskite solar cells

Physical vacuum deposition (PVD) of organo-metal halide thin film has advantages of uniform and large scale deposition for emerging perovskite solar cell technology. Evaporation of organic halides such as CH3NH3I (MAI) is crucial for obtaining phase pure perovskite thin films. However, controlling the evaporation rate of MAI remains difficult owing to its "vapor-gas" like nature upon sublimation. Here we report, highly crystalline CH3NH3PbI3 (MAPbI(3)) films with micrometer grains can be prepared by gradually controlling the MAI vapor pressure rather than evaporation rate in co-evaporation method. When integrating an optimal film into a planar heterojunction solar cell, the best device achieved a power conversion efficiency of 15.74% by deploying TiO2 as an electron transport layer. This strategy alleviates the strict calibration of MAI evaporation rate and led to obtain phase pure MAPbI(3) films for high performance solar cells.