Improved interface contact and defect passivation for enhanced charge dynamics of perovskite photovoltaics

Compact and uniform electron transport layers with additional functionality can effectively suppress carrier recombination and facilitate charge extraction. To regulate the preparation process and functionalize tin oxide (SnO2), potassium citrate is added into SnO2 solution to inhibit aggregation of SnO2 precursors. The incorporated carboxyl functional groups can improve film coverage and reduce interface traps. The additional K+ ions will penetrate into perovskite films and impede the formation of Frenkel defects to promote rapid charge separation and extraction. The functionalized SnO2 with high crystallinity can also improve fusion between nanocrystals and reduce grain boundaries. Enhanced electrical properties for the optimized SnO2 are realized using potassium citrate compared to single SnO2 due to the increased electron mobility. The conformal SnO2 film including carboxyl functional groups also forms a shielding layer against oxygen and water vapor permeation. A high power conversion efficiency of 23.95% (a VOC of 1.166 V, a JSC of 24.90 mA cm−2, and an FF of 0.825) is achieved for the champion device. The optimized device also shows the highly enhanced light/thermal stability. In addition, the whole charge dynamics (separation, extraction, and recombination) is discussed. Additionally, a simple strategy for scalable fabrication and commercialization of perovskite photovoltaics is provided based on the spin-coated SnO2 with functionality.