Electroluminescent Warm White Light-Emitting Diodes Based on Passivation Enabled Bright Red Bandgap Emission Carbon Quantum Dots.

The development of efficient red bandgap emission carbon quantum dots (CQDs) for realizing high-performance electroluminescent warm white light-emitting diodes (warm-WLEDs) represents a grand challenge. Here, the synthesis of three red-emissive electron-donating group passivated CQDs (R-EGP-CQDs): R-EGP-CQDs-NMe ₂ , -NEt ₂ , and -NPr ₂ is reported. The R-EGP-CQDs, well soluble in common organic solvents, display bright red bandgap emission at 637, 642, and 645 nm, respectively, reaching the highest photoluminescence quantum yield (QY) up to 86.0% in ethanol. Theoretical investigations reveal that the red bandgap emission originates from the rigid π-conjugated skeleton structure, and the -NMe ₂ , -NEt ₂ , and -NPr ₂ passivation plays a key role in inducing charge transfer excited state in the π-conjugated structure to afford the high QY. Solution-processed electroluminescent warm-WLEDs based on the R-EGP-CQDs-NMe ₂ , -NEt ₂ , and -NPr ₂ display voltage-stable warm white spectra with a maximum luminance of 5248-5909 cd m ^-2 and a current efficiency of 3.65-3.85 cd A ^-1 . The warm-WLEDs also show good long-term operational stability ( L / L ₀ > 80% after 50 h operation, L ₀ : 1000 cd m ^-2 ). The electron-donating group passivation strategy opens a new avenue to realizing efficient red bandgap emission CQDs and developing high-performance electroluminescent warm-WLEDs.
Competing Interests: The authors declare no conflict of interest.