Tailoring the Alkalinity of SnO2 Colloidal Suspension for High-Performance and Stable Perovskite Solar Cells

The commercial tin oxide (SnO 2 ) colloidal suspension is widely utilized as an electron transport layer (ETL) in high-performance perovskite solar cells (PSCs). However, despite significant efforts have been proposed to address bulk transport and interface recombination issues, the PSC efficiency is still limited to around 25%. In this study, the crucial role of the physicochemical characteristics of the SnO 2 colloidal suspension in shaping the morphology, electrical properties, and optical properties of the SnO 2 ETL is investigated. By controlling the pH value of the SnO 2 solution with weak acids such as carbonic acid, the reassembly of metal oxide nanoparticles into smaller sizes with more homogeneous dispersion and dense interconnections is successfully induced. Consequently, the resulting SnO 2 ETL exhibits enhanced crystallinity, high conductivity, low surface defects, and high optical transmittance. As a result, the efficiency of the target PSC is increased from 23.10% (control device) to 24.70%. This improvement is attributed to higher voltage, photocurrent, and fill factor compared to the relevant control samples. A similar device improvement using phosphoric acid is observed, indicating that the approach represents a universal technique to further enhance the quality of SnO 2 ETL for large-area, high-efficiency, and stable PSCs.