High-performance red phosphorescent light-emitting diodes built on bipolar host materials obtained from dibenzo[F,H]quinoxaline and dibenzothiophene

Abstract

DTBDQ, a bipolar host material with an acceptor unit dibenzo[F,H]quinoxaline and a donor unit dibenzothiophene connected by two interstitial benzenes, was employed. DTBDQ exhibits deep LUMO and HOMO energy levels, along with a triplet energy of 2.75 eV, owing to rational molecular design. Red phosphorescent organic light-emitting diodes (PhOLEDs) devices with DTBDQ here as the host and Ir(piq)2acac as the guest layer have an external quantum efficiency(EQE) of 19.79% with a limited roll-off and an EQE of 18.08% at 1000 cd/m2, with CIE coordinates of (0.68,0.32), which is quite comparable to the National Television Systems Committee (NTSC) CIE coordinates of (0.67,0.33). The device performance is significantly better than that of devices using hole-type host CBP, electron-type host TPBI, and electron and hole-type hosts together, indicating that the performance of bipolar host materials transferring both electrons and holes is superior to that of simply two hosts as a double light-emitting layer separately, which is beneficial to carrier transport balancing and avoiding carrier buildup. DTBDQ demonstrates that it is an excellent bipolar host candidate.