Enhanced performance and stability of ambient-processed CH3NH3PbI3-x(SCN)x planar perovskite solar cells by introducing ammonium salts

Metal halide perovskite solar cells have drawn a lot of attention due to their excellent photovoltaic properties. However, a simple method to prepare perovskite films with high quality in ambient air remains a big challenge, which has become an obstacle for the commercialization of PSCs. Here we propose a facile method to prepare efficient CH3NH3PbI3-x(SCN)(x)-based planar PSCs in ambient conditions and ammonium salts (NH4Cl, NH4SCN) are used to regulate the microstructure of CH3NH3PbI3-x(SCN)(x) perovskite film prepared in ambient air. At the optimal concentration, the devices with NH4Cl or NH4SCN additives achieve the champion efficiency of 14.71% and 16.61% respectively, which are much higher than the 12.97% of the reference device. The stability of the unsealed devices with additives in ambient air has also been significantly improved. The modified devices without any encapsulation still retain about 80% of initial efficiency after 30 days in ambient air. The conducive atomic force microscopy and photoluminescence measurement are used to characterize photoelectric properties of perovskite film. The trap-state density and charge recombination of the devices have been investigated. The results suggest that the improved photovoltaic characteristics and stability may be attributed to the improved quality of perovskite films, the reduced trap states and the suppressed charge recombination.