Room-Temperature Spray Deposition of Large-Area SnO₂ Electron Transport Layer for High Performance, Stable FAPbI₃-Based Perovskite Solar Cells

The performance and scalability of perovskite solar cells (PSCs) is highly dependent on the morphology and charge selectivity of the electron transport layer (ETL). This work demonstrates a high-speed (1800 mm min⁻¹), room-temperature (25 °C–30 °C) deposition of large-area (62.5 cm²) tin oxide films using a multi-pass spray deposition technique. The spray-deposited SnO₂ (spray-SnO₂) films exhibit a controllable thickness, a unique granulate morphology and high transmittance (≈85% at 550 nm). The performance of the PSC based on spray-SnO₂ ETL and formamidinium lead iodide (FAPbI₃)-based perovskite is highly consistent and reproducible, achieving a maximum efficiency of ≈20.1% at an active area (A) of 0.096 cm². Characterization results reveal that the efficiency improvement originates from the granular morphology of spray-SnO₂ and high conversion rate of PbI₂ in the perovskite. More importantly, spray-SnO₂ films are highly scalable and able to reduce the efficiency roll-off that comes with the increase in contact-area between SnO₂ and perovskite film. Based on the spray-SnO₂ ETL, large-area PSC (A = 1.0 cm²) achieves an efficiency of ≈18.9%. Furthermore, spray-SnO₂ ETL based PSCs also exhibit higher storage stability compared to the spin-SnO₂ based PSCs.