Energy-Level Modulation in Diboron-Modified SnO₂ for High-Efficiency Perovskite Solar Cells

Energy-level modulation between perovskite and carrier transport layers to obtain a promoted carrier extraction and reduced charge recombination is an effective way to achieve high-efficiency perovskite solar cells. Here, diboron is used as an effective interfacial modifier between SnO₂ and perovskite. By taking advantage of the higher Fermi level on the surface of SnO₂ after diboron treatment, a power-conversion efficiency of 22.04% in a solar cell device based on two-step solution-processed planar n-i-p structure is obtained. With the help of thorough characterizations, it is argued that the diboron-treated SnO₂ exhibits some Sn³⁺ species, which serve as electron donors with a more n-type nature, promoting electron extraction and reducing carrier recombination in the electron transport layer (ETL)/perovskite interface. Further analysis speculates that the formation of surface diboron–oxygen Lewis pair induces a reducing state of diboron complexes, resulting in the spontaneous electron redistribution and the formation of Sn³⁺−O^–• species. This provides an effective chemical approach to tune the energy alignment between the oxide ETL and absorber.