In situ passivation of Pb ⁰ traps by fluoride acid-based ionic liquids enables enhanced emission and stability of CsPbBr ₃ nanocrystals for efficient white light-emitting diodes

A great hurdle restricting the optoelectronic applications of cesium lead halide perovskite (CsPbX₃) nanocrystals (NCs) is due to the uncoordinated lead atoms (Pb⁰) on the surface, where most attempts to address the challenges in the literature depend on complicated post-treatment processes. Here we report a simple in situ surface engineering strategy to obtain highly fluorescent and stable perovskite NCs, wherein the introduction of the multifunctional additive 1-butyl-3-methyl-imidazolium tetrafluoroborate ([Bmim]BF₄) can significantly eliminate the Pb⁰ traps. The photoluminescence quantum yield (PLQY) of the as-synthesized NCs was improved from 63.82% to 94.63% due to the good passivation of the surface defects. We also confirm the universality of this in situ passivation pathway to remove Pb⁰ deep traps by using fluoride acid-based ionic liquids (ILs). Due to the high hydrophobicity of the cations of ILs, the as-prepared CsPbBr₃ NCs exhibit robust water resistance stability, maintaining 67.5% of the initial photoluminescence (PL) intensity after immersion in water for 21 days. A white light emitting diode (LED), assembled by mixing the as-synthesized CsPbBr₃ NCs and red K₂SiF₆:Mn⁴⁺ phosphors onto a blue chip, exhibits high luminous efficiency (100.07 lm W^-1) and wide color gamut (140.64% of the National Television System Committee (NTSC) standard). This work provides a promising and facile technique to eliminate the Pb⁰ traps and improve the optical performance and stability of halide perovskite NCs, facilitating their applications in optoelectronic fields.