Organic light-emitting diodes (OLEDs) have been considered as the most competitive candidates for solid-state lighting and new generation full color flat panel displays owing to advantages such as fast response, wide visual angle, low operating voltage for low power consumption high brightness, high contrast, and the possibility to produce thin, large area, and flexible devices. Solution-processed OLEDs that are prepared by the incorporation of phosphorescent dopants in host materials have generated a lot of interest in recent years because the can harvest both singlet and triplet excitons and also overcome the demerits of vacuum deposition processes. However, multilayer OLED fabrication from solutions requires that each underlying layer be resistant to the solvent used for the deposition of the next layer. A simple approach to solve this problem involves the use of an orthogonal solvent for spin-casting to deposit the subsequent layers. Yet another
approach involves using a cross-linkable materials, which can be solution-processed by spin-casting and then transformed into an insoluble film by light or thermal treatment. However, the light-induced cross-linking process may led to quenching of excitons by the photochemical initiator. In contrast, thermally cross-linkable
materials are attractive because they do not degrade the performance of the light-emitting device. In particular styrene-based materials have attracted a lot of attention as thermally cross-linkable materials for OLEDs, because free radicals are generated from a Diels-Alder styrene dimer by cross-linking at 150-200oC. In this study, we designed and synthesized thermally cross-linkable host materials and phosphorescent iridium(III) complexes for solution-processed organic light-emitting diodes (OLEDs). First, the synthesized thermally cross-linkable host materials containing styryl- and furyl- groups were thermally cross-linked by cross-linking at 150-200oC without using a polymerization initiator. For all cross-linked host material films, excellent solvent resistance was observed. A solution-processed red phosphorescence devices using synthesized thermally cross-linkable host materials were fabricated and its performance was evaluated. After films cross-linking, synthesized host materials demonstrated hole- and electron- transporting property, which indicated that it could be applied as a thermally cross-linkable host materials in solution-processed OLEDs. Second, A number of research groups published red, green and blue phosphorescent iridium(III) complexes for solution-processed OLEDs. However, the reported iridium(III) complexes have various problems, such as low photoluminescence (PL) quantum efficiency (ΦPL) and concentration self-quenching at high doping concentrations of OLEDs device. We designed and synthesized new green and blue homoleptic iridium(III) complexes containing trimethyl- and triisopropyl-phenyl substituted 2-phenylbenzoimidazole-based cyclometalating ligands for high thermal stability and improved quantum efficiency of phosphorescent OLEDs. And, we identified their geometrical configurations and crystal-packing structures using X-ray crystallography. We also found that the trimethyl- and triisopropyl-phenyl substituted 2-phenylbenzoimidazole-based cyclometalating ligands are important for preventing self-quenching in green and blue phosphorescent OLEDs at high dopant concentrations. The synthesized thermally cross-linkable host materials and phosphorescent iridium(III) complexes would be useful information for designing materials of solution-processed OLEDs.