Engineering Rhombus Carbon Quantum Dots for High-Performance Deep-Blue LEDs with External Quantum Efficiency Exceeding 4.5%

Achieving a high-performance carbon dots-based light-emitting device (CDLED) has long been a dream of the scientific community on account of its intrinsic merits of non-toxicity, cost-effectiveness, environmental-friendliness, and high stability. However, the bottleneck problems of low external quantum efficiency (EQE) and poor color purity limit the application of deep-blue CDLEDs. This work reports a series of rhombus CDs with a graphitized core and an alkyl passivation shell. The optimal m-CD exhibits a dramatically high photoluminescence quantum yield (PLQY) of 97.2% in solution and 82% in solid, exceeding all the previously reported CD materials for LED devices. The deep-blue CDLED using m-CD as an emitter demonstrates a bright, efficient, and high-color-purity emission, with a maximum luminance of 740.6 cd m–2, a maximum EQE of 4.51%, and CIE coordinates of (0.15, 0.07) closely approaching the high-definition television standard color Rec. BT.709 (0.15, 0.06) specification. The EQEmax of the m-CDLED device notably exceeds all previously reported blue LEDs using carbon quantum dots as emitters. This work will set the stage for developing the next generation of high-performance deep-blue CDLEDs.