Facilely synthesized carbon dots and configurated light-emitting diodes with efficient electroluminescence

Carbon dots (CDs) are recently emerging photoluminescence (PL) and electroluminescence (EL) emitters that are highly spotlighted in solid-state lighting. In this work, exceptional CDs with few defects, high carbonation, good film morphology and excitation wavelength-independent PL emission have been facilely synthesized and characterized with X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Superior EL emission from CDs has been demonstrated. With CDs as a single emissive layer, the light-emitting diode (LED) shows a maximum luminance of 19.34 cd m(-2), luminous efficiency of 0.037 cd A(-1), power efficiency of 0.039 lm W-1, and external quantum efficiency (EQE) of 0.031%. With poly(9-vinylcarbazole)/CDs as dual emissive layers, the LED shows a maximum luminance of 30.01 cd m(-2), luminous efficiency of 0.089 cd A(-1), power efficiency of 0.046 lm W-1, and EQE of 0.064%. The latter is better than the former because of the improved carrier balance and extended emission zone. The EL emission of both CD-based LEDs moves from the ultraviolet/blue emission of organics and/or interface emission to predominantly visible CD emission with increasing voltage. The evolution of EL and PL allows for a deeper understanding of the mechanism of CD emission and the advancement of CD-based LEDs.

Automated summary

In this study, high-quality carbon dots (CDs) with few defects, high carbonation, and good film morphology were successfully synthesized. The LEDs with CDs as the emissive layer showed superior emission performance, especially the ones with dual emissive layers. The mechanism of CD emission was attributed to the improved carrier balance and extended emission zone.