Optimization of the photoelectric properties and photo-stability of CH3NH3PbBrXI3-X films for efficient planar perovskite solar cells

In this paper, the CH3NH3PbBrXI3-X films were prepared by introducing CH3NH3Br into CH3NH3I precursor solution, after which the microstructure and photoelectric properties of the films were thoroughly investigated. Due to Br incorporation in the perovskite films, the band gap increased and the light absorption was slightly reduced while the charge carrier lifetime was prolonged due to the enhanced crystallinity. For the films with higher bromine content, the red shift of the photoluminescence peaks indicated that the phase segregation appeared in the films under illumination, which led to the formation of the iodine-rich domains in this process and the reduced carrier lifetime. On the contrary, for films with lower bromine content, the red shift of the photoluminescence peaks was negligible, which revealed that instability of the perovskite films under illumination can be suppressed by adjusting the bromine content of the films. Consequently, by moderate Br incorporation (CH3NH3Br/CH3NH3I mole ratio = 3:7), the CH3NH3PbBrXI3-X films with optimal photoelectric properties and photo-stability were achieved, and the stable photoelectric conversion efficiency of corresponding device under illumination can reach 13.8%.