The surface chemistry of ionic liquid-treated CsPbBr₃ quantum dots.

This article focuses on the interaction between phosphonium-based ionic liquids (ILs) from the CYPHOS family and all-inorganic CsPbBr₃ perovskite quantum dots (QDs) to elucidate ligand exchange mechanisms relevant to lead halide perovskite solar cells. Using solution ^1H NMR spectroscopy, the study demonstrates that the bromide-containing CYPHOS 102 IL effectively exchanges native oleylammonium and oleate ligands on the QD surface, resulting in a threefold increase in photoluminescence quantum yield (PLQY) without altering QD size or structure. In contrast, the hexafluorophosphate-containing CYPHOS 110 IL shows minimal ligand exchange and no improvement in PLQY. Excess CYPHOS 102 induces a phase transformation to a lead-deficient Cs₄PbBr₆ phase, while CYPHOS 110 does not, highlighting the role of anion coordinating ability in surface interactions and phase stability. These findings provide atomistic insight into IL-perovskite surface chemistry, informing the selective use of IL additives to enhance optoelectronic device performance.