Emitting-layer design of white organic light-emitting devices with single-host material

Efficient phosphorescence sensitization (PS) consisting of tris(phenylpyridine)iridium (Ir(ppy)(3)) sensitizers and 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran) (DCJTB) exciton acceptors in a host material, N, N'-dicarbazolyl-3,5-benzene, was implemented by a simplified emitting-layer structure with selectively doped DCJTB in the Ir(ppy)(3)-doped region. This codoped region away from the recombination zone peak in the Ir(ppy)(3)-doped region significantly improved the PS efficiency without affecting the carrier transport characteristics. Coupled with an efficiently phosphorescent blue emitter, iridium(III)bis[(4,6-di-fluoropheny)-pyridinato-N, C-2'] picolinate, a white organic light-emitting device utilizing this PS approach was demonstrated to have 10.94% external quantum efficiency, 17.4 cd/A and 12.2 lm/W at an applied voltage of 4.5 V, and a brightness of 107 cd/m(2) with Commission Internationale de l'Eclairage coordinates of (0.293, 0.427). With a 3 nm spacer for manipulating the exciton diffusion in the emitting layer, a slight CIE coordinates variation of (-0.008, -0.006) was obtained at practical luminance levels of 1000-4000 cd/m(2), evidence that PS was successfully achieved. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3176486]