Phosphate‐Buffered Synthesis of SnO ₂ Nanoparticles With Interfacial Proton Buffering for High‐Performance and Stable Perovskite Solar Cells

The electron transport layer (ETL) is essential for the performance and stability of perovskite solar cells (PSCs). SnO 2 nanoparticles, widely employed as the ETL in n‐i‐p PSCs, often exhibit performance limitations arising from uncontrollable agglomeration and compromised interfacial quality, which in turn accelerates perovskite degradation. In this study, we propose a phosphate‐buffered synthesis strategy for SnO 2 nanoparticles, which enables effective proton buffering both during the synthesis process and at the perovskite/SnO 2 interface. Through regulating proton accumulation during SnO 2 nanoparticle formation, the phosphate buffer simultaneously enhances the colloidal dispersion stability of SnO 2 and introduces coordinated phosphate species at the SnO 2 /perovskite interface in PSCs. This phosphate interface effectively stabilizes FA + cations and suppresses deprotonation‐induced interfacial degradation. Devices incorporating phosphate‐buffer‐synthesized SnO 2 deliver a peak power conversion efficiency (PCE) of 26.1% and exhibit remarkable operational stability, retaining over 85% of their initial efficiency after 1000 h of continuous light exposure. Meanwhile, large‐scale PSC modules (65cm 2 ) achieve a PCE of 21.74%. This synergistic strategy provides a scalable and efficient solution for enhancing both the performance and stability of PSCs.