Enhancing Efficiency and Stability of Perovskite Solar Cells via NaCl Post‐Treatment of SnO 2 Electron Transport Layers

Sodium chloride (NaCl) post‐treatment is employed as a simple and effective strategy to engineer SnO 2 electron transport layers (ETLs) for high‐performance perovskite solar cells. By directly comparing NaCl and KCl post‐treatments under identical processing conditions, the cation‐dependent effects on the SnO 2 /perovskite interface are systematically investigated. The NaCl‐treated SnO 2 surface exhibits improved wettability, facilitating uniform spreading of the perovskite precursor solution and promoting high‐quality perovskite film formation. Compared with KCl treatment, NaCl treatment results in lower surface roughness, improved film uniformity, enhanced interfacial charge extraction, and suppressed interfacial recombination. Optical and photoluminescence analyses reveal enhanced optical transmittance and more efficient carrier dynamics in NaCl‐treated devices. As a result, the optimized perovskite solar cells achieve a champion power conversion efficiency of 25.99% ( J sc = 26.13 mA cm −2 , V oc = 1.178 V, FF = 84.43%), compared with 24.11% for the KCl‐treated devices. In addition, the NaCl‐treated devices exhibit significantly improved dark‐storage stability, maintaining their performance over 1000 h in a nitrogen atmosphere. These results demonstrate that NaCl post‐treatment provides a practical and effective interface engineering strategy for simultaneously enhancing the efficiency and stability of perovskite solar cells.