Enhancement of green electroluminescence from 2,5-di-p-anisyl-isobenzofuran by double-layer doping strategy

A highly fluorescent compound, 2,5-di-p-anisyl-isobenzofuran (DABF), was synthesized and used as a dopant to fabricate efficient green electroluminescence (EL) devices. The highest occupied molecular orbital level of DABF suggests that it can be excited either by energy transfer or by direct charge trapping mechanism in the EL devices. Three kinds of devices were fabricated based on different emission mechanisms. A double-layer-doped device with DABF doped in both the hole-transporting layer and the electron-transporting layer of the ITO/NPB/TPBI/Mg:Ag device, where ITO is indium-tin-oxide, NPB is (4,4′-bisN-(1-naphthyl)-N-phenylamino]biphenyl), and TPBI is (2,2′,2″-(1,3,5-benzenetriyl)tris1-phenyl-1H-benzimidazole]), exhibited greatly enhanced brightness and efficiency comparing to the single-layer-doped devices. The brightness and efficiency enhancements are attributed to a combined contribution of energy transfer and direct charge trapping mechanisms in the double-layer-doped device.