Candlelight-style organic light-emitting diodes with high spectral resemblance via an energy relay system

Candlelight-style organic light-emitting diodes (OLEDs) are promising for eye-friendly lighting, yet simultaneously achieving a low correlated color temperature (CCT) and high spectral resemblance remains challenging. Here, an energy relay system is developed by elaborate coordination of exciplex, thermally activated delayed fluorescence, and phosphorescence, which regulates the dynamical behavior of excitons and achieves multi-emitter synergistic emission. The optimized device achieves maximum current efficiency, power efficiency, and external quantum efficiency of 26.0 cd/A, 31.4 lm/W, and 20.6%, respectively, while maintaining low blue-light-hazard efficacy and melatonin suppression sensitivity. More importantly, a candlelight-like emission with a CCT of 1855 K and a high spectral resemblance index of 92.4% is simultaneously achieved in the resulting device. These results demonstrate an effective strategy for efficient candlelight-style OLEDs combining low CCT with high spectral resemblance.