Thermally Activated Sensitized Fluorescence Enables Efficient Carbon Quantum Dot‐Based Electroluminescent LEDs with Current Efficiency of 31 cd A ⁻¹

Carbon quantum dots (CQDs) are gaining increasing attention as eco-friendly alternatives to conventional heavy-metal-based QDs for full-color displays and solid-state lighting. However, the performance of CQD-based light-emitting diodes (CQD-LEDs) remains significantly lower than their heavy-metal counterparts, primarily due to the substantial energy loss from triplet excitons during electrical excitation and the reduced quantum yield (QY) in solid films. Here, we present the demonstration of bright and efficient electroluminescent LEDs based on a thermally activated sensitized fluorescence (TSF) mechanism, employing a new class of solid-state emissive (SSE) CQDs that exhibit efficient orange emission in the solid state and bright green emission when doped into host materials, with a QY exceeding 80%. By employing thermally activated delayed fluorescence (TADF) materials as both hosts and sensitizers, along with highly efficient CQDs as dopants, we significantly enhance exciton utilization through effective Förster energy transfer from sensitizers to CQDs. This strategy results in bright, efficient green CQD-LEDs, achieving a maximum luminance of approximately 16,000 cd m^-2 and a record-high current efficiency of 31 cd A^-1. This work provides a straightforward and universal strategy for creating efficient SSE CQD-LEDs using the TSF strategy.