Managing Interfacial Defects and Charge-Carriers Dynamics by a Cesium-Doped SnO₂ for Air Stable Perovskite Solar Cells

A high-quality nanostructured tin oxide (SnO₂) has garnered massive attention as an electron transport layer (ETL) for efficient perovskite solar cells (PSCs). SnO₂ is considered the most effective alternative to titanium oxide (TiO₂) as ETL because of its low-temperature processing and promising optical and electrical characteristics. However, some essential modifications are still required to further improve the intrinsic characteristics of SnO₂, such as mismatch band alignments, charge extraction, transportation, conductivity, and interfacial recombination losses. Herein, an inorganic-based cesium (Cs) dopant is used to modify the SnO₂ ETL and to investigate the impact of Cs-dopant in curing interfacial defects, charge-carrier dynamics, and improving the optoelectronic characteristics of PSCs. The incorporation of Cs contents efficiently improves the perovskite film quality by enhancing the transparency, crystallinity, grain size, and light absorption and reduces the defect states and trap densities, resulting in an improved power conversion efficiency (PCE) of ≈22.1% with Cs:SnO₂ ETL, in-contrast to pristine SnO₂-based PSCs (20.23%). Moreover, the Cs-modified SnO₂-based PSCs exhibit remarkable environmental stability in a relatively higher relative humidity environment (>65%) and without encapsulation. Therefore, this work suggests that Cs-doped SnO₂ is a highly favorable electron extraction material for preparing highly efficient and air-stable planar PSCs.