Abstract
Although metal halide perovskites are candidate high‐performance light‐emitting diode (LED) materials, blue perovskite LEDs are problematic: mixed‐halide materials are susceptible to phase segregation and bromide‐based perovskite quantum dots (QDs) have low stability. Herein, a novel strategy for highly efficient, stable cesium lead bromide (CsPbBr3) QDs via in situ surface reconstruction of CsPbBr3–Cs4PbBr6 nanocrystals (NCs) is reported. By controlling precursor reactivity, the ratio of CsPbBr3 to Cs4PbBr6 NCs is successfully modulated. A high photoluminescence quantum yield (PLQY) of >90% at 470 nm is obtained because octahedron CsPbBr3 QD surface defects are removed by the Cs4PbBr6 NCs. The defect‐engineered QDs exhibit high colloidal stability, retaining >90% of their initial PLQY after >120 days of ambient storage. Furthermore, thermal stability is demonstrated by a lack of heat‐induced aggregation at 120 °C. Blue LEDs fabricated from CsPbBr3 QDs with reconstructed surfaces exhibit a maximum external quantum efficiency of 4.65% at 480 nm and excellent spectral stability.
Highlights
Introduction of perovskite light-emitting diode (LED)Metal halide perovskite materials have been recognized as promising candidates for next-generation color displays because their high photoluminescence quantum yields (PLQYs), narrowSeveral strategies for obtaining blue-emitting perovskites nanocrystals (NCs) are available
We investigated the effects of the Cs4PbBr6 NCs on the photophysical properties and thermal stability of the CsPbBr3 quantum dots (QDs) by observing changes in their morphology and optoelectronic properties
We synthesized a mixed solution of CsPbBr3 and Cs4PbBr6 NCs by modifying a previously reported synthetic method.[41]
Summary
We synthesized a mixed solution of CsPbBr3 and Cs4PbBr6 NCs by modifying a previously reported synthetic method (details provided in the Experimental Section).[41]. The absorption peak at 313 nm originated from optical transitions between localized states of the isolated [PbBr6]4− octahedron of Cs4PbBr6 NCs.[44,45,46] X-ray powder diffraction (XRD) patterns of the NCs allowed us to confirm that the first exciton peak is related to the bandgap of the luminescent CsPbBr3 NCs. the sample of synthesized NCs included both orthorhombic CsPbBr3 NCs and rhombohedral Cs4PbBr6 NCs, and the Cs4PbBr6-to-CsPbBr3 ratio increased as the reaction temperature decreased This result is consistent with the increase in the intensity of the absorption peaks at 313 nm in the UV–vis spectra. It should be noted that as the reaction temperature decreases, the PLQY increases from 57.7% to 90.1%, contrary to previously reported general trends of increasing crystallinity and PLQY with temperature (Figure 2i).[41]
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