A Surface Modifier Enhances Performance in All-inorganic CsPbI2Br Perovskite Solar Cells with Efficiencies Approaching 15%
All-inorganic perovskite solar cells (PSCs) are attracting considerable attention due to their promising thermal stability, but their inferior power-conversion efficiencies (PCE) hinder their realistic application. Here, we propose an approach through surface modification based on methyl ammonium halide (MAX) for inorganic CsPbI2Br solar cells processed with low temperature. The combined benefits with the introduced MAX modifier enable to boost the power conversion efficiency to 14.77% with an impressive FF of 82.20% in CsPbI2Br PSCs. Our experimental analyses coupled with optical modeling indicate that the incorporated MAX leads to an effective passivation of surface traps originating from Pb2+ and I- ions in CsPbI2Br and simultaneously mediates the crystallization of CsPbI2Br with slightly enlarged grains and reduced numbers of structural defects and pinhole. As a result, interfacial trap-assisted recombination is suppressed and charge extraction is promoted. Mechanistically, we show that in the presence of MAX, the deep-level traps in the perovskites are passivated, leaving the energy of trapping centers to become shallower. In this situation, the negative impacts of traps on carrier transport and recombination are mitigated.