Highly efficient pure yellow electrophosphorescent device by utilizing an electron blocking material
Yellow organic light-emitting devices (OLEDs) are not easy to obtain since yellow emissive materials are rare and the color purity is often perturbed by the emission from the carrier transport layer. A high-efficiency yellow-emission phosphorescent complex, iridium(III) bis(2-(9,9'-spirobi[fluorene]-7-yl)pyridine-N,C2') acetylacetonate ((SBFP)2Ir(acac)), is selected as the dopant material for yellow phosphorescent OLEDs (PHOLEDs). An electron blocking material, Ir(ppz)3 (ppz = phenylpyrazole), is utilized to restrain the blue emission from the hole transport layer and improve the color purity of yellow devices. The optimized device shows stable pure yellow electrophosphorescence with the Commission Internationale de l'Eclairage (CIE) coordinates of (0.46, 0.53), and the spectra are largely insensitive to the driving voltages. A maximum luminance of 37219 cd m−2, a maximum luminous efficiency of 50.6 cd A−1 and a maximum external quantum efficiency of 15.4% are obtained.