Stabilizing SnO ₂ Colloids via Phosphate Buffering for Efficient and Durable Perovskite Photovoltaics

SnO₂ nanoparticles (NPs) solutions are considered a highly efficient inks for fabricating electron transport layers in state-of-the-art solution-processed perovskite solar cells (PSCs). However, SnO₂ colloids exhibit thermodynamic instability in aqueous solution due to strong van der Waals attractions between nanoparticles, often leading to aggregation and precipitation. Here, a phosphate-buffered synthesis strategy is reported that effectively stabilizes SnO₂ colloids. The phosphate buffer maintains a stable pH during synthesis, dynamically regulating the electrostatic repulsion between nanoparticles to suppress aggregation and promote homogeneous dispersion. This method enables precise control over surface hydroxyl groups and oxygen vacancies in the resulting SnO₂ films, facilitating efficient electron transport and reducing interfacial recombination. As a result, PSCs achieve a high power convertion efficiency (PCE) of 26.40% while demonstrating exceptional operational stability. The encapsulated device maintains 99%, 84%, and 95% of their initial efficiency under ISOS-L-1, ISOS-L-2, and ISOS-O-1 protocols, respectively. Furthermore, a perovskite solar module (5 cm × 5 cm) with an active area of 12.6 cm² delivers an impressive PCE of 23.11%. These results highlight the scalability and practical viability of the strategy for developing large-area, high-performance photovoltaic modules.