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

A great hurdle restricting the optoelectronic applications of cesium lead halide perovskite (CsPbX) nanocrystals (NCs) is due to the uncoordinated lead atoms (Pb) on the surface, where most attempts to address the challenges in the literature depend on complicated post-treatment processes. Here we report a simple 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]BF) can significantly eliminate the Pb 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 passivation pathway to remove Pb deep traps by using fluoride acid-based ionic liquids (ILs). Due to the high hydrophobicity of the cations of ILs, the as-prepared CsPbBr 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 CsPbBr NCs and red KSiF:Mn phosphors onto a blue chip, exhibits high luminous efficiency (100.07 lm W) 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 Pb traps and improve the optical performance and stability of halide perovskite NCs, facilitating their applications in optoelectronic fields.