Managing Charge Balance and Triplet Excitons to Achieve High-Power-Efficiency Phosphorescent Organic Light-Emitting Diodes

Abstract

High-efficiency phosphorescent organic light-emitting diodes (PhOLEDs) have been achieved by using an ortho-linked triphenylamine/oxadiazole hybrid, namely p-TPA-o-OXD, as host material. The high HOMO level of the compound (5.25 eV) can facilitate efficient hole injection from 1, 4-bis[(1-naphthylphenyl)amino]biphenyl (NPB) layer to the emissive layer. As a result, low driving voltages and high power efficiencies have been attained as compared to the carbazole-based hosts with lower HOMO levels and higher injection barriers under similar device structures. By introducing 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) to replace 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(8-hydroxyquinoline)aluminum (Alq3) as hole blocking/electron transporting layer, followed by tuning the thicknesses of hole-transport NPB layer to manipulate the charge balance, high-efficiency PhOLEDs have been achieved, with maximum current efficiency/power efficiency/external quantum efficiency of 85.7 cd/A/99.7 lm/W/...