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

Abstract

Starburst-type hole-transporting and electron-transporting materials, tris(3-(9H-carbazol-9-yl)phenyl)amine (TmCTA), 2,4,6-tri([1,1 0 -biphenyl]-3-yl)-1,3,5-triazine (1), 2,4,6-tris(3 0 -methyl-[1,1 0 -biphenyl]-3-yl)-1,3,5-triazine (2), and 2,4,6-tris(3 0 ,5 0 -dimethyl-[1,1 0 -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 bis[2-(4,6-difluorophenyl)pyridinato-C 2 ,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.