Perovskite solar cells (PSCs) have rapidly emerged as leading photovoltaic contenders, achieving power conversion efficiencies (PCEs) exceeding 27% in both p-i-n and n-i-p configurations at laboratory scale.[1] These advancements stem from optimized perovskite compositions, interfacial engineering, and improved charge-transport layers (CTLs).[2, 3] While spin-coating remains the dominant method for fabricating high-efficiency PSCs, its scalability is limited. Transitioning to industrially compatible techniques poses challenges, particularly in depositing ultrathin (10–100 nm) and uniform electron and hole transport layers (ETLs/HTLs).[4-6] Consequently, developing scalable approaches for producing high-quality CTLs remains a critical step toward efficient and stable large-area PSCs.

The choice of transparent conducting oxide (TCO) substrate significantly influences CTL design and deposition. Indium tin oxide (ITO) offers superior transparency and conductivity but relies on scarce indium.[7-9] Fluorine-doped tin oxide (FTO) offers a viable and cost-effective alternative; however, its inherently rougher surface morphology (16–35 nm versus ~0.6 nm for ITO) complicates the deposition of conformal, pinhole-free CTLs by solution processing, often resulting in incomplete coverage and interfacial trap formation.[10, 11] Vacuum-based methods such as magnetron sputtering or atomic layer deposition can overcome these challenges, enabling uniform coatings on textured FTO surfaces.[9]

The predominant solution-based methods for depositing SnO2 films include chemical bath deposition (CBD) and colloidal dispersions.[12-15] Moreover, the ultrathin nature of these films (15–30 nm) makes them prone to pinhole formation, while CBD often requires long reaction times and yields films with uncontrolled oxygen vacancies.[16-18] To address these limitations, vacuum-based techniques such as radio-frequency (RF) magnetron sputtering have gained attention for producing uniform, stoichiometrically controlled SnO₂ layers. This solvent-free process allows the precise control over thickness and composition via sputtering power, deposition pressure, and O₂/Ar ratio.[19, 20]

Despite these advantages, PSCs incorporating sputtered SnO₂ typically achieve PCEs between 13.2% to 20.2%,[21-23] which remains below the 26.4% achieved with solution-based SnO2.[13, 15] This discrepancy is largely due to lower open-circuit voltage (Voc) and fill factor (FF), often attributed to elevated non-radiative recombination rates at the SnO2/perovskite interface.[13, 16] Such recombination is linked to complex surface states and oxygen-related defects generated during sputtering.[24-26]

This study presents a comprehensive evaluation of sputtered SnO₂ thin films, establishing correlations between structural, optical, chemical, and interfacial properties and the resulting PSC performance. By systematically tuning annealing temperature, oxygen concentration, and sputtering pressure, we identified processing windows that yield high-quality SnO₂ with enhanced crystallinity, reduced hydroxylation, optimized band alignment, and low surface recombination velocity (SRV). Target aging was found to significantly alter film stoichiometry and optical characteristics, necessitating oxygen compensation to maintain performance. Optimal conditions, 40% O₂ at 9 mTorr followed by annealing at 450 °C, produced the best films, achieving 20.7% efficiency, among the highest reported for sputtered SnO₂ without additional passivation.

Time-resolved photoluminescence and SRV analyses revealed that optimized sputtered SnO₂ interfaces approach the quality of nanoparticle-based ETLs, demonstrating that controlled vacuum deposition can rival solution-processed benchmarks. Drift-diffusion simulations incorporating experimental SRV and band-alignment data confirmed that interfacial recombination, rather than ETL transport limitations, governs device losses. Overall, this study elucidates how sputtering parameters dictate microstructure, defect chemistry, and energetics, providing clear design principles for scalable, high-performance SnO₂ ETLs .