Donor–Acceptor Biarylcarbazoles as Efficient Host Materials for Solution-Processable High-Performance Phosphorescent Organic Light-Emitting Diodes

Host materials having high triplet energies offer great commercial potential for the development of solution-processable high-performance phosphorescent organic light-emitting diodes (PhOLEDs). While plenty of vacuum-deposited host materials are available, the literature reveals a dearth of solution-processable host materials. Therefore, a series of biarylcarbazoles (BACs) were designed as host materials by incorporating donor–acceptor functionalities and doped with blue, green, yellow, and orange phosphorescent emitters to develop energy-saving high-performance PhOLEDs with low turn-on voltages. All of the synthesized host materials exhibited good thermal stability in the range of 294–355 °C and exhibited remarkably high triplet energies of 2.50–2.81 eV. Surprisingly, PhOLEDs prepared by incorporating a host material 6a doped with a green phosphorescent emitter, i.e., Ir­(ppy)3, displayed admirable efficiencies with a maximum power efficiency (PE) of 55.6 lm/W, a current efficiency (CE) of 53.2 cd/A, and an external quantum efficiency of 17.1% with a maximum brightness (L max) of 27 000 cd/m2. BAC host material 6a exhibited better performance compared to that of commercial host 4,4′-bis­(N-carbazolyl)-1,1′-biphenyl (CBP) and 4,4′,4″-tris­(carbazol-9-yl)­triphenylamine. The BAC 6a host was also found to be compatible with orange, yellow, and blue phosphorescent emitters, which displayed PEs of 31.9, 21.4, and 14.1 lm/W, respectively, at a brightness of 100 cd/m2. Notably, the green PhOLED with donor–acceptor-based host 6a exhibited 23% roll-up in CE while moving from 100 to 1000 cd/m2. The enhancement of the performance of the green PhOLED is attributed to higher singlet and triplet energies of host 6a compared to that of the utilized green emitter tris­(2-phenylpyridine)­iridium­(III), leading to effective host–guest energy transfer and the ability to form efficient excitons in the host–guest matrix, thus enhancing the OLED performance. Thus, BAC 6a has commercial potential as a suitable host material for the fabrication of efficient multicolor PhOLEDs.