pH-Controlled Synthesis of SnO₂ Electron Transport Layers for High-Efficiency and Stable Perovskite Solar Cells

The synthesis methods of SnO₂ electron transport layer critically determine the performance of the perovskite solar cells (PSCs), as it governs the particle size, crystallinity, dispersibility, and surface chemistry. In this study, we systematically investigated how the pH (acidic, neutral, or alkaline) during the synthesis of SnO₂ affects the efficiency and stability of PSCs. The acidic-derived SnO₂ (AC-SnO₂) features a carboxyl-rich surface that promotes strong hydrogen bonding with FA⁺ cations but also accelerates iodide (I^-) oxidation. In contrast, the alkaline-derived SnO₂ (AL-SnO₂) contains a high density of oxygen vacancies, which facilitate the decomposition of the perovskite into Pbl₂. Notably, the neutral-synthesized SnO₂ (N-SnO₂) provides optimal interface properties, yielding a champion active-area efficiency of 26.10% for small-area cells (0.09 cm²) and 23.10% for mini-modules (14 cm²). This work highlights the central role of synthesis pH in tailoring interfacial chemistry and achieving high-performance, stable PSCs.