Hybridized local and charge-transfer phosphafluorene oxide-based emitter for efficient nondoped blue organic light-emitting devices

Abstract

The aryl phosphine oxide (APO) groups have been widely studied as host materials in organic light-emitting diodes (OLEDs). However, their application as emissive materials has been rarely explored, especially in the preparation of nondoped devices. In this work, two hybridized local and charge-transfer (HLCT) molecules, 2tBuCz-APO and 2TPA-APO, are developed by incorporating the donor groups tert-butylcarbazole (tCz) and diphenylamine (DPA) into phosphafluorene oxide unit. The experimental results demonstrate that phosphafluorene oxide derivatives exhibit HLCT characteristics, marking the first time that HLCT characteristics have been realized based on APO. As a result, the nondoped OLED based on 2tBuCz-APO exhibits the best performance with an excellent maximum external quantum efficiency (EQE_max) of 7.3 % and Commission Internationale de l’Éclairage (CIE) coordinates of (0.14, 0.15). This molecular design strategy has demonstrated that phosphine oxide, as an acceptor unit, shows promising potential for the development of highly efficient nondoped OLEDs.