FAPbBr3/Cs4PbBr6 Core/Shell Perovskite Nanocrystals with Enhanced Stability and Emission: Implications for LEDs

Formamidinium lead bromide (FAPbBr3) nano crystals (NCs) have been demonstrated to exhibit ideal ultrapure green luminescence at 530 nm and to hold great potential in light emitting diodes, by potentially overcoming the difficulties facing cesium lead bromide (CsPbBr3) NCs. However, compared to all inorganic lead halide perovskite NCs, organic-inorganic hybrid FAPbBr3 NCs are sensitive to moisture, oxygen, and heat due to their intrinsic instability caused by the organic cations (FA+). Herein, we present an epitaxial growth method for the overgrowth of a large-band-gap cesium lead halide (Cs4PbBr6) shell on the surface of FAPbBr3 NCs. The resulting core/shell NCs show a near-unity photoluminescence quantum yield (PLQY) of 97.1%, the emission with full width at half-maxima of 88 meV, and longterm environmental stability. The introduction of Cs+ into FAPbBr3 NCs can inhibit the migration of FA+ and suppress the phase transformation from cubic phase to tetragonal phase at 60 ?. Furthermore, the existence of shell can provide stronger exciton confinement and improve the thermal stability of FAPbBr3 NCs. The core/shell perovskite NCs developed in this study have the advantages of high PLQY and good stability and may contribute to the field of light-emitting diodes (LEDs).