Ultrastable Inorganic Perovskite Nanocrystals Coated with a Thick Long-Chain Polymer for Efficient White Light-Emitting Diodes

The unstable nature of perovskites has severely limited their practical applications. Here, we report on ultrastable CsPbBr3 nanocrystals (NCs) with a thick (similar to 25 nm) polymer coating prepared via an effective postsynthetic strategy. The thick poly(maleic anhydride-alt-1-octadecene) (PMAO) with long hydrophobic alkyl chains bounded with the surface ligands of perovskite NCs acts as a protection layer to effectively prevent perovskite degradation from the external environment. The photoluminescence (PL) for the thick PMAO-coated CsPbBr3 NCs maintains more than 90% of its initial emission intensity under continuous ultraviolet illumination of 144 h, whereas that of the pristine NCs is decreased to similar to 6%. After exposure in air for 40 days, only a very little PL degradation appears for the thick polymer-coated NCs as compared to the dramatic decrease in the PL emission for the pristine NCs. Upon immersion into water for 24 h, the perovskite NCs maintain 60% of its initial PL intensity, whereas the PL emission for the pristine NCs is completely quenched within only a few minutes. Moreover, there is no any side effect on the luminescent properties of perovskite NCs by the transparent polymer coating and the PL quantum yields are obviously improved due to the surface defect passivation of NCs. The resulting thick PMAO-coated CsPbBr3 NCs are combined with a commercially available red-emitting phosphor on a blue InGaN chip to fabricate a high-performance warm white light-emitting diode with a high power efficiency of 56.6 lm/W.