Carbon Quantum Dots with Near-Unity Quantum Yield Bandgap Emission for Electroluminescent Light-Emitting Diodes

Carbon quantum dots (CQDs) feature bright and tunable photoluminescence, solution processability, and low toxicity, showing great potential in optoelectronics. However, the large-scale synthesis of CQDs with near-unity photoluminescence quantum yield (PLQY) has not been achieved so far. In this study, we perform radical-assisted synthesis of hexagon-shaped CQDs (H-CQDs) delivering near-unity PLQY (96 %). Experimental and theoretical analyses revealed that the large vertically oriented transition dipole moment of H-CQDs originating from high symmetry results in nearly 100 % PLQY. The H-CQDs also exhibited a high electron mobility of up to 0.07 cm²  V^-1  s^-1 . These properties enable the H-CQD-based light-emitting diodes with a high external quantum efficiency of 4.6 % and a record maximum brightness of over 11 000 cd m^-2 . This study represents a significant advance that CQDs-based electroluminescent device can be utilized for potential display and lighting applications.