Carbon Dot Based Multicolor Electroluminescent LEDs with Nearly 100% Exciton Utilization Efficiency

Carbon dots (CDs) are promising nanomaterials for next-generationlighting and displays due to their tunable bandgap, high photoluminescencequantum yield (PLQY), and high stability. However, the exciton utilizationefficiency (EUE) of CD-based films can only reach 25%, fundamentallylimiting their application in electroluminescent light-emitting diodes(LEDs). Improving the EUE is therefore of great significance. Herein,we developed composite films containing CDs and poly(9-vinylcarbazole)(PVK). The films were then used to construct a series of high-performanceelectroluminescent LEDs with tunable emission colors covering theblue to green regions as the concentration of CDs in the films increased,delivering a maximum external quantum efficiency and current efficiencyof 2.62% and 5.11 cd/A, respectively. Theoretical calculations andexperiments established that the excellent performance at low filmPLQY was due to a hot exciton effect in the CDs, achieving nearly100% EUE. This work provides new design strategies toward high-performanceCD-based electroluminescent LEDs.