Co²⁺-Tuned Tin Oxide Interfaces for Enhanced Stability of Organic Solar Cells

The electron transport layers (ETLs) are one of the crucial factors for realizing the high performance of inverted organic solar cells (OSCs). In inverted OSCs, zinc oxide (ZnO) is a widely used n-type semiconductor as the ETL material. However, when exposed to ultraviolet (UV) light, ZnO induces decomposition of organic materials. Tin dioxide (SnO₂) has higher conductivity, higher electron mobility, wider bandgap, and weaker absorption of UV light, which is thought to be one of the promising ETLs. Unfortunately, a SnO₂ ETL is suffering from high work function (WF), which greatly decreases the ability of charge transport and collection. Here, we induce a facile strategy to reduce the WF of SnO₂ by Co²⁺ tuning. The Co²⁺-tuned SnO₂ exhibits a low WF of 3.64 eV, holding high transmittance and high conductivity. The OSCs based on PM6:Y6 with a Co²⁺-SnO₂ ETL show a notable power conversion efficiency of 15.3%, which is superior to those of the OSCs with ZnO and SnO₂ ETLs. The OSCs with a Co²⁺-SnO₂ ETL under continuous UV light and light-emitting diode irradiation exhibit a more robust photostability relative to OSCs with pristine SnO₂ ETLs. The trap densities of Co²⁺-SnO₂ films are lower than that of the SnO₂ film, which may contribute to enhanced stability of OSCs.