Controlled HCl etching of Al₂O₃ nanoparticles toward void-free interfacial contact for efficient perovskite solar...

Preferential nucleation at the upper surface of formamidinium-cesium (FA/Cs) perovskite films typically leads to porous structures at the bottom interface. Pre-depositing Al₂O₃ nanoparticles can enhance nucleation at the bottom interface, thereby suppressing void formation. However, this approach relies heavily on the dispersion behavior of the Al₂O₃ nanoparticles. Unfortunately, commercial Al₂O₃ pastes suffer from severe agglomeration. Herein, we report a simple acid-assisted ultrasonication treatment to achieve controllable etching of commercial Al₂O₃, which significantly improves its dispersibility in solution. This allows the use of a lower Al₂O₃ concentration to enable compact contact between the FA/Cs perovskite film and the substrate. The reduced amount of Al₂O₃ not only improves the crystallinity of the perovskite film but also enhances interfacial electron injection. As a result, FA_0.95Cs_0.05-based perovskite solar cells achieve a power conversion efficiency of 25.28% with a fill factor exceeding 82%. A 16 cm² mini-module reaches an efficiency of over 22%. Unencapsulated devices retain 90% of their initial efficiency after 1000 h of continuous operation, demonstrating the excellent scalability potential of this approach.