Fluorescence/phosphorescence hybrid WOLEDs using a novel green pure organic phosphor with high CRI values and stable EL spectra

Fluorescence/phosphorescence hybrid white organic light-emitting diodes (WOLEDs) are promising for next-generation solid-state lighting due to their high efficiencies and enhanced device stability. However, achieving high efficiencies, high CRI values, and highly stable white EL spectra simultaneously remains a formidable challenge. Meanwhile, pure organic phosphors applied in WOLEDs are still rare. To address this issue and evaluate the potential of pure organic phosphors in WOLEDs, we simplified the device structure by using the mCP:PO-T2T exciplex and inserted a newly-designed pure organic green phosphor Se-1 in trichromatic fluorescence/phosphorescence hybrid WOLEDs. Se-1 can give broadband pure room-temperature phosphorescent emission without any residual fluorescent emission and high PLQY of 0.78. The simplified device structure helps improve the white EL spectral stability. The TADF and bipolar transport features of the mCP:PO-T2T exciplex and high PLQY of Se-1 are good to boost the EL efficiencies. The broadband emission of the mCP:PO-T2T exciplex and Se-1 facilitates high CRI values. Eventually, the optimal WOLEDs (Device W9) can show a very stable white EL spectra in a broad driving voltage range with CIE coordinate changes of Δx and Δy being only 0.01 and achieve high EL efficiencies with maximum external quantum efficiency of 11.4%, maximum current efficiency of 26.5 cd A⁻¹, and maximum power efficiency of 27.8 lm·W⁻¹, respectively, and high CRI values up to 83. This work should not only highlight the great potential of pure organic phosphors in WOLED applications, but also provide important design guideline for developing organic-phosphor-based fluorescence/phosphorescence hybrid WOLEDs with high efficiencies, CRI values, and highly stable white EL spectra, simultaneously.