Reactive Sputtering of SnO2 Electron Transport Layers for Perovskite Solar Cells

Sputtered SnO2 has the potential to be a scalable electron transport layer (ETL) for perovskite solar cells (PSCs). However, its performance lags that of solution-processed counterparts due to high interfacial recombination. In this work we systematically investigate the roles of oxygen concentration, reaction pressure and thermal annealing on the structural, optical, and electronic properties of sputtered SnO2 films. It is found that elevated annealing at temperatures of up to 450 °C are required to improve the crystallinity and densify the deposited films. Concurrently, higher deposition pressures are needed to reduce the impurity levels and oxygen vacancies within the films. Under these conditions, improved energy level alignment is further achieved with the FA0.88Cs0.12PbI3 perovskite used in this study. Such optimized SnO2 thin films are found to exhibit comparable surface recombination velocities to nanoparticle analogues, thus achieving efficiencies of up to 20.7%. Drift-diffusion simulations are used to validate the sequential enhancements in performance enabled by the process modifications and identify areas for further improvement. Collectively, these results establish a foundation for continued efficiency improvements and the scalable fabrication of high-performance PSCs employing sputtered SnO₂ ETLs.