High-Fill-Factor Perovskite Solar Cells via Pseudohalide Salt Modification of the Substrate to Mitigate Nonradiative...

The utilization of the sol-gel method for fabricating planar SnO₂ as the electron transport layer (ETL) induces numerous defects on the SnO₂ layer surface and perovskite film bottom, causing considerable deterioration of the device performance. Conventional inorganic salt-doped SnO₂ precursor solutions used for passivation may cause incomplete substrate coverage due to the presence of inorganic salt crystals, further degrading the device performance. Here, a substrate modification approach involving the pretreatment of a fluorine-doped SnO₂ (FTO) substrate with NH₄PF₆ is proposed. The interaction between PF₆^- ions and the FTO substrate enhances SnO₂ film quality; excess PF₆^- ions decrease the number of defects on the film surface. NH₄⁺ ions react with an -OH stabilizing agent in the SnO₂ solution and are eliminated during annealing. The combined effects suppress nonradiative recombination and ion migration at the ETL-perovskite interface. The corresponding high-quality perovskite solar cells (PSCs) exhibit a fill factor of ∼0.825; PSC efficiency increases from 19.59% to 22.32%.