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Potassium Iodide Doping Strategy for High-Efficiency Perovskite Solar Cells Revealed by Ultrafast Spectroscopy.

Organic-inorganic halide perovskites are promising materials for high-performance photovoltaics. The doping strategy is considered to be an effective method for regulating the performance of perovskite solar cells, yet its efficiency is still far below what has been anticipated. Here, we systematically investigate the regulatory mechanisms of the performance of perovskites by exploiting potassium iodide (KI) doping. We find that the surface states are passivated apart from the modified lattice structure. Most importantly, carrier recombination and transport are regulated by varying two different trap states when doping KI. The corresponding defect penalty can be effectively restrained at an optimal concentration of added KI (5%). A significant increase in the conductivity and radiative efficiency is achieved under such conditions. Our results provide fundamental insights into defect engineering through doping and a promising route toward highly efficient perovskite solar cells.