A Redox-Active\nIonic Liquid Surface Treatment for\nHealing CsPbBr<sub>3</sub> Nanocrystals

Additive engineering\nof lead halide perovskites has been a successful\nstrategy for reducing a variety of deleterious defect types. Ionic\nliquids (ILs) are a unique group of such additives that have been\nused to passivate halide vacancies in both bulk lead halide perovskites\nand their colloidal nanocrystal analogues. Herein, we expand the types\nof defects that can be addressed through IL treatments in CsPbBr<sub>3</sub> nanocrystals with a novel phosphonium tribromide IL that\nheals metallic lead surface defects through redox chemistry. This\nnew type of surface treatment leads to a significant increase in PLQY\nand outperforms equivalent treatments with non-redox-active bromide\nILs. Such redox-active ligands widen the scope of defect types that\ncan be addressed in semiconductor nanocrystals.