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

The utilization of the sol-gel method for fabricating planar SnO 2 as the electron transport layer (ETL) induces numerous defects on the SnO 2 layer surface and perovskite film bottom, causing considerable deterioration of the device performance. Conventional inorganic salt-doped SnO 2 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 SnO 2 (FTO) substrate with NH 4 PF 6 is proposed. The interaction between PF 6 - ions and the FTO substrate enhances SnO 2 film quality; excess PF 6 - ions decrease the number of defects on the film surface. NH 4 + ions react with an -OH stabilizing agent in the SnO 2 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%.