Unprecedented Matrix‐Induced Emission Enhancement Enables Bright and Efficient Carbon Quantum Dot‐Based Electroluminescent Light‐Emitting Diodes

Abstract Carbon quantum dots (CQDs) are promising environmentally friendly alternatives to conventional heavy‐metal‐based quantum dots for light‐emitting diodes (LEDs). Traditional CQDs typically exhibit high photoluminescence quantum yields (PLQYs) in dilute solutions, but their PLQY significantly drops when embedded in host matrix—a widely adopted strategy in CQD‐LEDs fabrication. This limitation severely restricts the device performance. A conceptually new class of CQDs that exhibit unprecedented matrix‐induced emission enhancement (MIE) behavior is reported, enabling the fabrication of bright and efficient electroluminescent LEDs. These MIE‐CQDs show a low PLQY of 15% in solution, which increases to over 70% when embedded in a host matrix. Comprehensive structural, optical, and photophysical analyses attribute the MIE effect to the restriction of intramolecular motions in their non‐planar structure, effectively suppressing non‐radiative recombination. By employing a thermally activated delayed fluorescence material as the host matrix and MIE‐CQDs as dopants, LEDs with a maximum luminance exceeding 10,000 cd m −2 and a high current efficiency over 20 cd A −1 is achieved. Notably, devices using MIE‐CQDs directly as the emissive layer peaking at 603 nm also demonstrated impressive luminance of up to 8366 cd m −2 . This work presents an effective strategy for designing efficient MIE‐CQDs, promising for high‐performance LED applications.