In a homojunction device, a single organic layer assumes the multiple roles of hole, electron transportation, and emitter. Its ease in processing is highly desirable from the manufacturing point of view. In this paper, we shall describe the synthesis of a range of bipolar small molecules and conductive vinyl polymers for application in homojunction and heterojunction organic light emitting diodes (OLEDs). The bipolar materials, in general, consist of three basic building blocks: an arylamine, a 1,3,4-oxadiazole, and a polycyclic aromatic moiety. The achievement of charge balance can be validated either by direct measurement of electron/hole mobility or indirectly via optimization of device properties. A series of conductive vinyl copolymers containing hole transporting N-(4-methoxyphenyl)-N-(4-vinylphenyl) naphthalen-1-amine (4MeONPA) and electron transporting 2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (OXA) at different compositions was applied for heterojunction and homojunction OLEDs. For heterojunction devices employed the copolymers as the hole transporting layer and Alq 3 as the electron transporting and emitting layer, a maximum luminance and current efficiency of over 23000 cd/m 2 and 4.2 cd/A (PL of Alq 3 ), respectively, were achieved at the charge balance composition. Homojunction devices for the copolymers were demonstrated by the addition of rubrene as a dopant. The single layer devices at the optimal copolymer composition has ca 1500 cd/m 2 and 0.74 cd/A.

No abstract

A number of novel vinyl monomers containing either a fluorescent or a phosphorescent moiety were synthesized. The vinyl monomers have either hole or electron transporting properties and luminescence in near-UV, blue, green, to red. The overall charge transport properties and emission hue can be tuned by applying and the various monomers at different mix ratios.The vinyl monomers were copolymerized into high molecular weight yet soluble conductive copolymers using traditional solution free radical polymerization method.The vinyl monomers prepared including electron transporting 11-vinyl-phenanthro[9.10-b]quinoxaline (QP) and 1-vinyl pyrene (PY), hole transporting 9-(4-methoxyphenyl)-3-vinyl-9H-carbazole (KPA) and N-phenyl-N-(4-vinylphenyl) naphthalene -1-amine (NPA), and a red-emitting phosphorescent monomer based on the Europiujm complex [Eu(DBM) 3 H-EtPIP]. The optical, thermal and electrical properties of the copolymers were characterized. Homojunction OLED based on the copolymers were prepared by spin-coating. The EL spectra and I-V-L characteristics were obtained and will be reported.