In this review, we describe the syntheses and properties and application to liquid crystal displays（LCD）of liquid crystalline dendrimers（LD）having peripheral mesogenic units, which can be prepared by the reaction between a commercial polypropyleneimine dendrimer and acrylates having mesogenic units,and which exhibit spontaneous homeotropic orientation on glass. The effect of dendrimer generation, spacer length and mesogenic structure on the homeotropic orientation is also described. When LD（up to 1 wt％）are dissolved into nematic liquid crystals（NLCs）, this orientation can be induced to whole NLCs. A test cell with a combined mixture of LD and positive NLCs with a comb electrode can repeatedly switch between voltage-off dark and voltage-on bright states. The LD-induced homeotropic orientation could be applied to TFT liquid crystal display without using any polyimide alignment layers.
Generally, organic transistors have field-effect transistor structure, where current flows in the plane of the organic film, and the channel length is determined by fine patterning technique. In contrast, vertical-type organic transistors have sandwich structure composed of organic/metal/organic layers, where current flows in vertical direction. In this structure, very short channel length can be achieved because it corresponds to the film thickness. In addition, current flows in whole area of the device. As a result, the vertical-type organic transistors are very suitable for high current and high frequency operation. Recently, we have proposed novel vertical-type organic transistors named the metal-base organic transistor（MBOT）. In this report, we review device performance, operation mechanism, application and materials for MBOTs.
The development of dyes that exhibit a broad absorption band from the visible to the near-infrared region is crucial to harvest sunlight efficiently in dye-sensitized solar cells（DSSCs）. For the realization of the wide-band dyes, utilization of the forbidden transition from the singlet ground state to the triplet excited state is considered to be one of the important methods, whereas the transition is very rare and very weak in normal dyes for DSSCs. With this mind, we have investigated novel panchromatic terpyridyl Ru（II）complex sensitizer which shows specific spin-forbidden absorption in the near IR region. The DSSC with the dye-adsorbed nanocrystalline TiO2 electrode shows efficient photoelectric conversion over the whole visible range extending into the near-IR region up to 1000 nm, and overall energy conversion efficiency was highest among tandem organic photovoltaics.
Solution processes such as spin-coating, inkjet-printing, or die-coating for organic light emitting devices (OLEDs) are fascinating due to their potential advantages for a production of large area devices at low cost. One of the key solutions to improving the performance of the devices is stacking of a number of successive layers of different functional materials. This multilayer architecture allows for the separation of the charge-injecting, charge-transporting, and light-emitting functions to different layers, which leads to a dramatic increase in efficiency and lifetime. We have developed various solution-processable OLED materials. In this review, we report our recent studies on fluorescent emitters, phosphorescent emitters, host materials, cross-linkable host materials, and electron injection materials for solution-processed OLEDs.
A great deal of attention has been devoted to organic electronics due to its application to large-area, low-cost, and flexible electronics, and a wide variety of organic semiconductors have been developed for organic transistors. Here we describe recent development of high performance organic transistor materials and ambipolar materials from the viewpoint of the energy levels. By considering contact resistance coming from the interfacial potential at the organic/electrode boundary, we introduce our recent attempt to develop self-contact organic transistors using chemical doping.
Within Fraunhofer COMEDD a roll-to-roll line for research and development for OLED lighting on metal and barrier films has been brought into operation. The roll-to-roll line consists of a vacuum coater for small molecule depositions; a roll-to-roll encapsulation unit for lamination under inert atmosphere and an optical inspection system for defect characterization. White emitting OLEDs on meter long substrates have been demonstrated. Beside the challenging deposition technology a proper encapsulation is the key issue for further development. In general, the performance of a barrier film will be mainly benchmarked with the water vapor transmission rate, but on the other hand adhesion compatibility, mechanical stability, defect level and residual water left in the barrier stack or adhesive are also of interest. In particular particle contamination on barrier film substrates may negatively affect the OLED lifetime. This is caused by local elevated leakage current which could result in cumulative dark spot growths on active OLED areas. Novel R2R inspection concepts have been developed within the roll-to-roll line to determine defect densities for different defect types. Additionally, the detected defects can be visualized in bin size distributions to allow a better understanding of the OLED device performance and degradation mechanisms.