Dimethylphenacylsulfonium tetrafluoroborate (DMPSBF₄) as a novel bulk passivator for FAPbI₃ perovskite films is introduced. DMPSBF₄-treated films exhibit longer carrier lifetimes, enhanced photophysical properties, and improved moisture stability despite a slight reduction in crystallinity. These results highlight the potential of sulfonium-based additives to enhance bulk defect passivation and improve the operational stability of perovskite solar cells.

The long-term operational stability of perovskite solar cells (PSCs) remains a major hurdle for commercialization, primarily due to bulk defects and ion migration within the perovskite layer. In this work, dimethylphenacylsulfonium tetrafluoroborate (DMPSBF₄) as a novel bulk passivating agent for formamidinium lead iodide (FAPbI₃) perovskite films is explored. Despite a reduction in film crystallinity upon incorporation of DMPSBF₄, treated films exhibit enhanced photophysical properties and improved moisture stability. Time-resolved photoluminescence measurements reveal longer carrier lifetimes, suggesting effective suppression of non-radiative recombination pathways. Solid-state nuclear magnetic resonance spectroscopy confirms the formation of chemical interactions between DMPSBF₄ and the perovskite lattice, providing insights into its passivation mechanism. Moreover, stability studies demonstrate that DMPSBF₄-treated films maintain enhanced moisture stability under ambient conditions over extended periods. These findings underscore the potential of sulfonium-based additives as promising alternatives to conventional ammonium-based compounds for enhancing bulk passivation and long-term stability in PSCs.