Perovskite solar cells (PSCs) adopting inverted planar heterojunction architectures have attracted considerable attention because of the low-temperature solution processing of all functional layers, versatility of energy-band engineering, and a simplified device structure[1, 2]. However, their low power conversion efficiency (PCE) (typically <20%) in comparison to over 22% reported for the best cells based on mesoporous-TiO2 regular structure[3, 4], becomes a critical challenge for the future large-scale applications. To overcome these scientific challenges, we report that the mixed-cation perovskite films containing formamidinium have enabled to deposit onto the PTAA hole-selective contact layer by dual-source precursor solution, and this results in a rapid rise in PCE that exceeded 20%. Subsequently, we further obtain more perfect perovskite films via controlling the defects densities both inside grain boundaries and at the surface, in case average Urbach energy of mixed-cation mixed-halide perovskite film is reduced to 14.2 meV. Ultimately, we’ve achieved over 21.5% PCE in inverted structure PSCs that is comparable to the regular perovskite solar cells containing mesoporous TiO2.
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