Hot Exciton Carbon Dots‐Based Deep Blue Electroluminescent Light‐Emitting Diodes Exceeding 7% External Quantum Efficiency

Abstract Carbon dots (CDs) have emerged as an exceptional material for the emission layer in the new generation of electroluminescent light‐emitting diodes (ELEDs) owing to their low cost, high stability, and high luminous efficiency. Although blue CDs‐based ELEDs have a wide bandgap and a low exciton utilization efficiency (EUE), it is still challenging to increase their external quantum efficiency (EQE). Although thermally activated delayed fluorescence and triplet‐triplet annihilation may improve EUE, the design of blue ELEDs is complicated by the significant charge transfer characteristics introduced by the low energy spitting of T1 and S1. This research effectively produced blue‐emitting CDs using a heated exciton process by carefully selecting precursors to overcome the aforementioned challenges. Deep blue and blue ELEDs based on CDs are developed by manipulating the electron‐hole mobility and the energy level structure of the device. The EQEs of these ELEDs exceeded those of previously reported CDs‐based blue ELEDs by over 7%. This study presents design concepts for new CDs and introduces a novel approach to develop cost‐effective, environmentally friendly, and highly efficient metal‐free blue ELEDs.