Highly Emissive Blue Quantum Dots with Superior Thermal Stability via In Situ Surface Reconstruction of Mixed CsPbBr3 -Cs4 PbBr6 Nanocrystals.

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 -Cs4 PbBr6 nanocrystals (NCs) is reported. By controlling precursor reactivity, the ratio of CsPbBr3 to Cs4 PbBr6 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 Cs4 PbBr6 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.