Novel Hole-Transporting Materials with High Triplet Energy for Highly Efficient and Stable Organic Light-Emitting Diodes

Demonstration of highly efficient organic light-emitting diodes (OLEDs) is becoming commonplace; however, there have been few reports on hole-transporting materials (HTMs) designed for highly efficient and stable green OLEDs. Here, operationally stable HTMs with high triplet energy were synthesized by incorporating dibenzothiophene and dibenzofuran into hole-transporting amino groups. The triplet energy of the amine derivative with dibenzothiophene was increased from 2.35 to 2.56 eV by introducing o,o'-quaterphenyl without impairing the stability. Since the largest triplet energy of the synthesized HTMs is 2.59 eV, the triplet excitons of green phosphorescent emitters and thermally activated delayed fluorescence (TADF) emitters are confined effectively. The operational stability of the phosphorescent OLED (PHOLED) using the synthesized HTM was about 15 times longer than that of the PHOLED using 2,2'-bis(3-ditolylaminophenyl)-1,1'-biphenyl. The optimized green PHOLED exhibits EQE of over 20% for a luminance of 10 to 10,000 cd m(-2) and an expected half lifetime of over 10,000 h with an initial luminance effective for improving the efficiency of OLEDs incorporating a green TADF emitter, of 1000 cd m(-2). The synthesized HTM is as well as green phosphorescent OLEDs.