Solvent‐Free Synthesis of Ultrabright Carbon Dots With Near‐Unity Quantum Yield for High‐Performance Light‐Emitting Diodes

ABSTRACT

Conventional liquid‐phase syntheses of carbon dots (CDs) often involve complex solvent‐precursor interactions that induce structural and spectral heterogeneities, severely limiting their optoelectronic performance. Herein, we report a highly controlled, solvent‐free, single‐precursor strategy utilizing 2,6‐diaminonaphthalene to synthesize ultrabright, highly uniform green‐emissive CDs (DAN‐CDs). Through comprehensive thermal analyses and kinetic modeling, we elucidate a spatiotemporally resolved, dual‐pathway formation mechanism: a nitrogen‐doped core initially assembles within an oxygen‐shielding autogenic precursor melt, followed by controlled, oxygen‐mediated surface passivation as the melt barrier attenuates. This self‐limiting oxidative capping thoroughly suppresses non‐radiative structural defects. Photophysical analyses uncover an efficient intra‐particle energy funneling process from the light‐harvesting core to these surface traps, yielding excitation‐independent green emission with a narrow bandwidth (< 60 nm) and a near‐unity photoluminescence quantum yield of 91%. When integrated into self‐emissive light‐emitting diodes (LEDs), the devices deliver pure green electroluminescence. Notably, the peak external quantum efficiency (EQE) of 2.2% achieved herein through the solvent‐free approach stands as the highest value reported to date among LEDs based on green‐emissive CDs synthesized via thermal carbonization. These results conclusively underscore the strong potential of rationally designed DAN‐CDs as highly efficient, environmentally benign, and heavy‐metal‐free emitters for next‐generation optoelectronics and display applications.