Repairing Defects of Halide Perovskite Films To Enhance Photovoltaic Performance.

On account of the low-temperature solution fabrication, the much high defect density at the interfaces and grain boundaries of halide perovskite films is recognized as one of the big obstacles toward high-efficiency solar cells. Here, the time-resolved photoluminescence (TRPL) with incident light exciting from the upper surface and bottom of halide perovskite films, respectively, showed very different results, verifying the much more surface trap states in the film. To eliminate the defects and enhance the photovoltaic properties of perovskite solar cells (PSCs), we designed a facile and effective method to repair the defects of the perovskite film using formamidinium iodine (FAI) solution. The dissociative FA+ and I- ions could compensate for the loss of volatile organic cations and also fill the I- vacancies of halide perovskites. After repairing defects with proper concentration of FAI solution, the TRPL curves obtained by light exciting from the different sides of the perovskite film nearly overlap together, indicating the reduction of surface traps. As a result, both the total carrier lifetime and charge extractions were improved by removing the nonradiative channels (surface traps), which universally enhanced the power conversion efficiency and stability of the planar heterojunction structural PSCs.