Improvement of photovoltaic performance of the inverted planar perovskite solar cells by using CH3NH3PbI3−xBrx films with solvent annealing

In this paper, the CH3NH3PbI3−xBrx films with various Br-doping contents were successfully prepared by solution processed deposition and followed by annealing process. This method simultaneously modified the morphology and composition of the CH3NH3PbI3 film. The effects of annealing treatment of CH3NH3PbI3−xBrx films under N2 and DMSO conditions on the microstructure of films and photoelectric properties of the solar cells were systematically investigated. The relationship of the component ratio of RBr/I= CH3NH3PbI3−xBrx/CH3NH3PbI3 in the resulting perovskite versus CH3NH3Br concentration also was explored. The results revealed that the CH3NH3PbI3−xBrx films annealed under DMSO exhibited increased grain sizes, enhanced crystallinity, enlarged bandgap and reduced defect density compared with that of the N2 annealing. It also was found that the RBr/I linearly increased in the resulting perovskite with the increased of CH3NH3Br concentration in the methylammonium halide mixture solutions. Furthermore, the photovoltaic performances of devices fabricated using DMSO precursor solvent were worse than that of DMF under N2 annealing atmosphere. When CH3NH3Br concentration was 7.5 mg ml−1, the planar perovskite solar cell based on CH3NH3PbI3−xBrx annealed under DMSO showed the best efficiency of 13.7%.