Candlelight-based, blue-hazard free lighting sources are friendly to the human eye, physiology, museum artifacts, ecosystems, the environment, and the night sky.

Solution processing enables organic devices to be fabricated cost-effectively, while deep-red emitters enable displays with high color saturation and lighting with high light quality. However, limited deep-red emitters were reported with solutionprocess feasibility and high efficiency. We demonstrate here a high-efficiency, solution-process-feasible deep-red emitter by coupling the highly efficient phosphorescent complex with a highly thermally stable fluorescent compound. The device exhibits a maximum external quantum efficiency of 11.2% at 10 cd m −2 and 8.4% at 100 cd m −2 . The latter is coupled with an ultradeep red emission (0.70, 0.27) and a potential color saturation of 108%. Besides the intrinsically high-efficiency nature of the phosphorescent complex, the record high efficiency may be attributable to the spirally configured fluorene moiety in the fluorescent compound to prevent concentration-quenching effect, a proper host to enable an effective host-to-guest energy transfer, and the employed cohost with electron-trapping character to enable a balanced carrier injection.

High light-quality and low color temperature are crucial to justify a comfortable healthy illumination. Wet-process enables electronic devices cost-effective fabrication feasibility. We present herein low color temperature, blue-emission hazards free organic light emitting diodes (OLEDs) with very-high light-quality indices, that with a single emissive layer spin-coated with multiple blackbody-radiation complementary dyes, namely deep-red, yellow, green and sky-blue. Specifically, an OLED with a 1,854 K color temperature showed a color rendering index (CRI) of 90 and a spectrum resemblance index (SRI) of 88, whose melatonin suppression sensitivity is only 3% relative to a reference blue light of 480 nm. Its maximum retina permissible exposure limit is 3,454 seconds at 100 lx, 11, 10 and 6 times longer and safer than the counterparts of compact fluorescent lamp (5,920 K), light emitting diode (5,500 K) and OLED (5,000 K). By incorporating a co-host, tris(4-carbazoyl-9-ylphenyl)amine (TCTA), the resulting OLED showed a current efficiency of 24.9 cd/A and an external quantum efficiency of 24.5% at 100 cd/m2. It exhibited ultra-high light quality with a CRI of 93 and an SRI of 92. These prove blue-hazard free, high quality and healthy OLED to be fabrication feasible via the easy-to-apply wet-processed single emissive layer with multiple emitters.

Yellow emission plays an important role in many display and lighting applications, such as RGBY display or blue hazard free lighting sources, while a wet-process enables soft devices to be manufactured cost-effectively.