Ultrafine SnO2 colloids with enhanced interface quality for high-efficiency perovskite solar cells

Perovskite solar cells (PSCs) with a certified power conversion efficiency (PCE) exceeding 25% commonly employ SnO2 electron transport layers (ETLs) fabricated via chemical bath deposition (CBD) or commercial colloids. However, CBD is time consuming, while commercial colloids lack precise control over properties crucial for high PCE. Developing a superior SnO2 colloidal solution with ultrafine particles, minimal defects, and homogeneous dispersibility for low-defect interfaces with perovskite is essential. We present a method to synthesize SnO2 colloids in H2O2 solution, yielding 4–6 nm particles with reduced oxygen vacancies. Sonication and formamidinium chloride (FACl) addition promote defect-free interface formation with perovskites. Utilizing SnO2-FACl ETLs, we achieve high-performance PSCs with a remarkable PCE of 26.05% (certified 25.54%). This success stems from reduced defects in the ETL and favorable charge transport with the perovskite film, offering a promising route for manufacturing high-quality SnO2 ETLs crucial for highly efficient PSCs, with significant commercialization potential.