The
unstable nature of perovskites has severely limited their practical
applications. Here, we report on ultrastable CsPbBr3 nanocrystals
(NCs) with a thick (∼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 ∼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.
Tunable color temperature of graphene quantum dot-based white lighting emitting diodes had been achieved adjusting the thickness and concentration of color convert matrix.
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