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-center dot species. This provides an effective chemical approach to tune the energy alignment between the oxide ETL and absorber.