High-Efficiency Phosphorescent White Organic Light-Emitting Diodes with Stable Emission Spectrum Based on RGB Separately Monochromatic Emission Layers

Abstract

Highly efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable emission spectra are successfully fabricated by using an RGB three-color separately monochromatic emission layer (EML) structure. The EML consists of a sequence of bis(2-methyldibenzo[f, h]quinoxaline) (acetylacetonate) iridium (III) (Ir(MDQ)2 (acac)) doped tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as the red emission layer, iridium, tris(2-phenylpyidine)(Ir(ppy)3) doped TCTA as the green emission layer and iridium(III) [bis(4, 6-difuorophenyl)-pyridinato-N, C2′]picolinate (FIrpic) doped a mixed-host of TCTA and tris(4-carbazoyl-9-ylphenyl)amine (26DCz PPy) as the blue emission layer. Without using any out-coupling techniques, the resulting WOLEDs achieve a power efficiency of 42lm/W at 100 cd/m2, and 34 lm/W at 1000 cd/m2. The WOLEDs also show excellent spectrum stability with bias voltages, remaining the Commission Internationale de L'Eclairage coordinates at (0.44, 0.43) from 1000 cd/m2 to 10000 cd/m2 and the color rendering index is as high as over 80. We contribute the stable emission spectrum to the RGB separate EML structure that successfully suppresses the undesired competition between host-guest energy transfer and direct exciton formation on emissive dopants by effectively controlling the position of exciton recombination region.