Blue Phosphorescent Organic Light-emitting Diode Using a Novel Starburst-type Donor and Acceptor Material as a Co-host

摘要

Starburst-type hole-transporting and electron-transporting materials, tris(3-(9H-carbazol-9-yl) phenyl) amine (TmCTA), 2,4,6-tri(1,1'-biphenyl-3-yl)-1,3,5-triazine (1), 2,4,6-tris(3'-methyl-1,1'-biphenyl-3-yl)1,3,5- triazine (2), and 2,4,6-tris(30,50-dimethyl-1,1'-biphenyl-3-yl)-1,3,5-triazine (3) having high triplet energies and excellent thermal stabilities were synthesized. Deposited films of TmCTA, with 1, 2, or 3 as hosts, were doped with the blue phosphorescent dopant bis2-(4,6-difluorophenyl) pyridinato-C2, N(picolinato) iridium(III) (FIrpic) and their device characteristics were evaluated. In co-deposited films, the molecular weight ratio of TmCTA to 1, 2, or 3 was 1: 1, and these co-hosts formed exciplexes. By comparison with those of single-host systems, the PL spectra of the co-deposited films were red-shifted, suggesting that exciplexes are formed by the two constituent molecules. When doped with 10 FIrpic, TmCTA: 1 device showed an external quantum efficiency (EQE) of 14.56 (maximum 16.46) at 1000 cd/m(2); similar results were obtained for the remaining films. The EQE roll-offs in the co-host systems are much smaller than those of single-host device using TmCTA.