A Bipolar Transporter as an Efficient Green Fluorescent Emitter and Host for Red Phosphors in Multi- and Single-Layer Organic Light-Emitting Diodes

Multifunctional donor-acceptor compound 4,4-bis(dibenzothiophene-S,S-dioxide-2-yl)triphenylamine (DSTPA) was obtained by linking a strongly electron-withdrawing core and a strongly electron-donating core with a biphenyl bridge in linear spatial alignment. DSTPA not only has suitable HOMO and LUMO levels for easily accepting both holes and electrons, it was also demonstrated to have a high fluorescence quantum yield of 0.98 and a high triplet energy level of 2.39eV. Versatile applications of DSTPA for bipolar transport, green fluorescent emission, and sensitizing a red phosphor were systematically investigated in a series of multi- and single-layer organic light-emitting devices. In traditional multilayer devices, it shows excellent performance both in an undoped fluorescent device (used as a green emitter and achieving maximum current and power efficiencies (CE and PE) of 12.6cdA(-1) and 9.4LmW(-1), respectively) and in a red phosphorescent device (used as a host and achieving maximum CE and PE of 26.4cdA(-1) and 26.3LmW(-1), respectively). Furthermore, DSTPA was also simultaneously used as an emitter, a hole transporter, and an electron transporter in a single-layer device showing CE and PE of 5.1cdA(-1) and 4.7LmW(-1), respectively. A single-layer red phosphorescent device with efficiencies of 11.7cdA(-1) and 12.6LmW(-1) was obtained by doping DSTPA with a red phosphor. The performances of all of the devices in this work are comparable to the best of their corresponding classes in the literature.