Matrix-Free Thermally Activated Delayed Fluorescent Carbon Dots-Based Electroluminescent Light-Emitting Diodes Exceeding 5.6% External Quantum Efficiency.

Carbon dots (CDs) are promising luminescent emission layer materials for next generation electroluminescent light emitting diodes (EL-LEDs) due to their many advantages, such as environmental friendliness, low cost, and high stability. However, limited by the spin-forbidden properties of the triplet transition, it is difficult to improve the external quantum efficiency (EQE) of fluorescent CDs-based EL-LEDs. Meanwhile, traditional thermally activated delayed fluorescent (TADF) CDs prepared using coating strategies are difficult to utilize in EL-LEDs due to the nonconductivity of the coating agent. Herein, we successfully developed matrix-free TADF CDs with yellow emission and achieved a device EQE of 5.68%, which is the highest value reported in CDs-based EL-LEDs. In addition, we also developed white EL-LEDs with an EQE of 1.70%. This study highlights the importance of interactions between precursors in modulating the electroluminescence properties of TADF emitters and provides an effective design principle for matrix-free TADF CDs.