High-efficiency white light emission using a phosphorescent sensitizer in organic light-emitting devices

Abstract

We have fabricated white organic light-emitting devices by using the phosphorescent material fac tria (2-phenylpyridine) iridium [Ir(ppy 3)] as a sensitizer, as a result, the efficiency of these devices is improved dramatically. Ir(ppy)3 and the fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl) (DCITB) are co-doped into 4,4′-N,N′-dicsrbazole-biphenyl (CBP) host, whose thickness affects both color and efficiency of the devices. Tris (8-hydroxyquincline) aluminum (Alq) and 2,9-dimethyl-4,7-diphenyl-1,10- phenanthroline (bathocuproine or BCP) are used as electron-transporting and exciton-blockiag layers, respectively, and N,N′-diphenyl-N,N′-bis(1. naphthyl)-(1,1′-biphenyl)-4,4′diamine (NPB) as a blue light-emitting as well as hole-transporting layer. The maximum efficiencies of the devices with 15 and 20 nm co-doped BCP tuning layer are 7.5 and 8.6 cd/A, respectively, and the former presents fairly pure white emission with CIE coordinates of (0.33, 0.32) at 10 V, which is very stable at various biases (10 19V).