Robust, Brighter Red Emission from CsPbI₃ Perovskite Nanocrystals via Endotaxial Protection

Increasing the stability of lead halide perovskites (LHPs) is required for integrating them into light-emitting devices. To date, most studies toward this direction have primarily concentrated on improving the chemical stability of green-emitting LHPs. In this work, red-emitting CsPbI₃-Cs₄PbI₆ hybrid nanocrystals (NCs) were synthesized with a high photoluminescence (PL) quantum yield of ∼90%. Their hybrid structure was examined via structural (Rietveld) refinement analysis and transmission electron microscopy. Rietveld refinement also revealed that the black polymorph of CsPbI₃ NCs is an orthorhombic perovskite rather than a cubic one. The thermodynamic stability of the CsPbI₃ NCs in Cs₄PbI₆ matrices is enhanced in both solutions and films for up to several weeks. The enhanced stability of the embedded CsPbI₃ NCs is attributed to the lowering of their Gibbs free energy, as determined on the basis of experimental data. Additionally, the hybrid NCs exhibit unprecedented emission stability-maintaining 65% of their original PL efficiency at 150 °C-and improved aqueous stability.