Incorporating a tercarbazole donor in a spiro-type host material for efficient RGB phosphorescent organic light-emitting diodes

Abstract

The exploitation of universal spiro-type hosts suitable for full-color phosphors is still a bottleneck for fabricating highly efficient phosphorescent organic light-emitting diodes (PHOLEDs) with a similar device structure. In this work, a novel spiro-configured host 3,6-di(9H-carbazol-9-yl)spiro[indolo[3,2,1-de]acridine-8,9′-thioxanthene]10′,10′-dioxide (TCZSO₂) incorporating 9′H-9,3′:6′,9′′-tercarbazole and 9H-thioxanthene 10,10-dioxide moieties is designed and synthesized. Utilizing 9′H-9,3′:6′,9′′-tercarbazole as the building-block in designing new spiro-type host materials in organic light-emitting diodes (OLEDs) is seldom reported. In particular, the three color-based devices based on TCZSO₂/bis(4,6-(difluorophenyl)pyridinato-N,C2′)picolinate (FIrpic), TCZSO₂/iridium(III) bis(2-phenylpyridinato-N,C2′)acetylacetonate (Ir(ppy)₂(acac)) and TCZSO₂/iridium(III) bis(2-methyldibenzo[f,h]quinoxaline)acetylacetonate (Ir(MDQ)₂(acac)) exhibit respectable external quantum efficiencies (EQEs) of 22.8%, 24.0% and 21.0%, respectively. More encouragingly, blue and green PHOLED devices have quite low efficiency roll-off (EQE: 22.7%/24.0%, FIrpic/Ir(ppy)₂(acac)) at a high brightness of 1000 cd m⁻². At a higher brightness of 5000 cd m⁻², there is only 5.3% and 4.6% decrease in EQEs from their maximum values, indicating a very low efficiency roll-off. These excellent results confirm a novel spiro-type host design strategy for incorporating reported electron donors with high triplet energy (E_T) to achieve high-performance RGB PHOLEDs.