Deep‐Blue Electroluminescent Light‐Emitting Diodes with Efficient Hot‐Exciton Emission from Carbon Quantum Gear Rack

Abstract The quest for exemplary color purity, superior efficiency, and nontoxic deep‐blue electroluminescence remains paramount for developing wide‐color‐gamut displays. However, achieving a Commission Internationale de l'Eclairage y value below 0.05, an exceptional external quantum efficiency (EQE), and a low‐efficiency droop in deep‐blue emitters presents a significant challenge. Here, the study reports a deep‐blue emitting carbon quantum gear rack (DB‐CQG) characterized by an emission wavelength of 406 nm and a high quantum yield of 80%. DB‐CQG comprises nine benzene rings and four embedded nitrogen‐centered tripods and exhibits a quasi‐planar configuration that leads to hybridized local and charge‐transfer (HLCT) excited‐state characteristics. Both experimental investigations and theoretical calculations revealed the activation of the reverse intersystem crossing channel between the high‐lying triplet state and lowest excited singlet state in DB‐CQG via hot‐exciton mechanism. DB‐CQG exhibits characteristic HLCT behavior with deep‐blue emission owing to the partial overlap of holes and electrons, which is facilitated by the formation of nitrogen‐centered tripods in the quasi‐planar configuration. The electroluminescent light‐emitting diodes (LEDs) fabricated using DB‐CQG exhibit a deep‐blue color with chromaticity coordinates of (0.158, 0.048), a maximum luminance of 4560 cd m −2 , and an EQE of 10.45%, which is one of the highest reported efficiencies for solution‐processable deep‐blue LEDs.