Hybrid white organic light-emitting diodes with high color-rendering index and stable color

Abstract

High efficiency hybrid white organic white light-emitting diodes (WOLEDs) for high color-rendering index (CRI) and stable color have been fabricated by the design of device structures. Here we fabricated two kinds of hybrid WOLEDs with red phosphorescent emissive layer/green phosphorescent emissive layer/spacer/blue fluorescent emissive layer (device 1) and red phosphorescent emissive layer/spacer/blue-green emissive layer (device 2), respectively. The key point in device 1 is using mixed 4,4′,4″-Tri(9-carbazoyl) triphenylamine (TCTA) and bis[2-(2-hydroxyphenyl)-pyridine] beryllium (Bepp2) as the host of phosphorescent EMLs as well as the spacer, which broadens the exciton distribution and improve the effective control of charge carriers in emissive layers. As a result, the hybrid WOLED exhibits a high power efficiency of 27.1 lm/W at brightness of 1000 cd/m2 and also a stable spectral emission with a high color rendering index (CRI) of 89 in a whole range of luminance. For device 2, the simultaneous emission of a blue light from the fluorescent host (Bepp2) and a green light from the phosphor (Ir(ppy)2(acac)) was realized by controlling the doping concentration of the green phosphor in the fluorescent host. It can be seen that the resulting hybrid WOLEDs achieved a CRI of 90 and kept rather stable spectral emission with Commission Internationale de L’Eclairage (CIE) coordinates of (0.42, 0.44) independent of driving voltages. This device2 also emits a high power efficiency of 23.0 lm/W at 1000 cd/m2.