Stable and Bright Electroluminescent Devices utilizing Emissive 0D Perovskite Nanocrystals Incorporated in a 3D CsPbBr3 Matrix

The 0D cesium lead halide perovskite Cs4PbBr6 has drawn remarkable interest due to its highly efficient robust green emission compared to its 3D CsPbBr3 counterpart. However, seizing the advantages of the superior photoluminescence properties for practical light‐emitting devices remains elusive. To date, Cs4PbBr6 has been employed only as a higher‐bandgap nonluminescent matrix to passivate or provide quantum/dielectric confinement to CsPbBr3 in light‐emitting devices and to enhance its photo‐/thermal/environmental stability. To resolve this disparity, a novel solvent engineering method to incorporate highly luminescent 0D Cs4PbBr6 nanocrystals (perovskite nanocrystals (PNCs)) into a 3D CsPbBr3 film, forming the active emissive layer in single‐layer perovskite light‐emitting electrochemical cells (PeLECs) is designed. A dramatic increase of the maximum external quantum efficiency and luminance from 2.7% and 6050 cd m−2 for a 3D‐only PeLEC to 8.3% and 11 200 cd m−2 for a 3D–0D PNC device with only 7% by weight of 0D PNCs is observed. The majority of this increase is driven by the efficient inherent emission of the 0D PNCs, while the concomitant morphology improvement also contributes to reduced leakage current, reduced hysteresis, and enhanced operational lifetime (half‐life of 129 h), making this one of the best‐performing LECs reported to date. Highly luminescent 0D Cs4PbBr6 nanocrystals are incorporated into 3D CsPbBr3 films to form single‐layer perovskite light‐emitting electrochemical cells. The 0D Cs4PbBr6 nanocrystals improve the maximum luminance to 11 200 cd m−2, the power efficiency to 33.0 Lm W−1, the external quantum efficiency to 8.3%, and the operational stability to 129 h at 10 mA cm−2.