pH‐Controlled Synthesis of SnO ₂ Electron Transport Layers for High‐Efficiency and Stable Perovskite Solar Cells

ABSTRACT The synthesis methods of SnO ₂ 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 SnO ₂ affects the efficiency and stability of PSCs. The acidic‐derived SnO ₂ (AC‐SnO ₂ ) features a carboxyl‐rich surface that promotes strong hydrogen bonding with FA ⁺ cations but also accelerates iodide (I ⁻ ) oxidation. In contrast, the alkaline‐derived SnO ₂ (AL‐SnO ₂ ) contains a high density of oxygen vacancies, which facilitate the decomposition of the perovskite into Pbl ₂ . Notably, the neutral‐synthesized SnO ₂ (N‐SnO ₂ ) provides optimal interface properties, yielding a champion active‐area efficiency of 26.10% for small‐area cells (0.09 cm ² ) and 23.10% for mini‐modules (14 cm ² ). This work highlights the central role of synthesis pH in tailoring interfacial chemistry and achieving high‐performance, stable PSCs.