Synergistic Defect Suppression and Stress Relief for Efficient Spray-Coated SnO₂-Based Perovskite Solar Cells

The scalable fabrication of high-performance SnO₂ electron transport layers (ETLs) via solution processing is hindered by colloidal aggregation and defect proliferation, which degrade perovskite solar cell (PSC) efficiency and stability. Here, we developed an in situ coordination strategy using l-aspartic acid monosodium salt (ASP-Na) to address these challenges. The carboxyl groups of ASP-Na form stable complexes with Sn⁴⁺, suppressing colloidal aggregation and enhancing interparticle electrostatic repulsion, thereby improving solution dispersion stability and reducing oxygen vacancy (O_V) density. The resultant spray-coated SnO₂ films exhibit compact morphology and optimized energy-level alignment. Buried interface analysis confirms a suppressed defect density on the perovskite surface close to ETL accompanied by interfacial-stress alleviation, facilitating vertically aligned perovskite grain growth and mitigating defect-mediated nonradiative recombination. Consequently, the ASP-Na-modified devices achieve a champion power conversion efficiency (PCE) of 24.27%, with suppressed hysteresis and enhanced operational stability, retaining over 90% of their initial PCE after 1600 h of ambient aging. This work provides a defect suppression and stress relief paradigm, advancing the scalable solution-based fabrication of high-efficiency, industrially compatible perovskite photovoltaics.