New soluble host materials with benzocarbazole and triphenyltriazine moieties, 11-[3-(4,6-diphenyl-[1,3,5]triazin-2-yl)-phenyl]-11H-benzo[a]carbazole and 11-[3'-(4,6-diphenyl-[1,3,5]triazin-2-yl)-biphenyl-4-yl]-11H-benzo[a]carbazole, were synthesized for highly efficient red phosphorescent organic light-emitting diodes (PHOLED). Hole-transporting benzocarbazole moiety and electron transporting triphenyltriazine moiety, which are severely twisted each other enhance the solubility of those materials in common organic solvent. The improved solubility from this molecular design could be due to a reduced π-π stacking interaction, which gives a very uniform film morphology after spin coating of those materials. As a result, we obtained highly efficient soluble PHOLEDs combined with an evaporated blue common layer structure. The resultant red PHOLED exhibited the maximum current efficiency as well as external quantum efficiency values up to 23.7 cd/A and 19.0%.

The impact of anode buffer layers (ABLs) on the performance of CdSe quantum-dot light-emitting diodes (QLED) with a ZnO nanoparticle (NP) electron-transport layer and 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) hole-transport layer was studied. Either MoO3 or 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) was used as the ABL. The QLED with a HAT-CN ABL exhibited better luminance performance, while the ultraviolet photoelectron spectroscopy and hole-only devices indicated that MoO3 was a superior hole injector. These results suggest that the QLED with a MoO3 ABL suffered from a severe charge carrier imbalance. Therefore, electron injection through the ZnO NP layer must be improved to further enhance the QLED performance.

We have studied a pixel-isolated phase-separated composite organic film (PI-PSCOF). This PI-PSCOF is used for anisotropic phase separation from ferroelectric liquid crystals (FLCs) and prepolymer materials using an appropriate UV intensity variation. In this device, the FLC molecules are isolated in the pixels where FLCs are surrounded by the interpixel vertical polymer walls and the horizontal polymer films on the upper substrate. These devices show very short response time and very high mechanical durability against external pressure. We also compared the pure FLC, conventional phase-separated composite film (PSCOF) and PI-PSCOF mode in terms of their electrooptic characteristics and X-ray layer structure measurements. Compared with the PSCOF mode, PI-PSCOF exhibits good electrooptical behaviors. Consequently, we achieved an excellent device scheme suitable for flexible substrates, using the PI-PSCOF mode and expect that this PI-PSCOF scheme will be one of the powerful and promising new FLC display modes, particularly applicable to flexible FLC display modes.

We have fabricated highly efficient green phosphorescent organic light-emitting diodes by solution process. Very interestingly, we found that the device efficiency is affected by interface between hole transport layer (HTL) and emission layer (EML). It was proved through spin cleaning process of cross-linkable HTL after curing which may affect the interface mixing. In addition, we tried to add complement layer to manipulate such effects. As a result, we significantly improved device efficiency (up to 72.7 cd/A) after spin cleaning process of the cross-linkable HTL material.

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