The relationship between molecular shape of fluorescent blue dopants (BDs) IntroductionSome companies have started mass production of OLED TVs or OLED lighting. One of the most critical issues for OLED application is the reduction of power consumption due to the revision of power consumption regulation by "Energy Star" program or other commissions. Regarding phosphorescent devices, the performance of red or green devices has been dramatically improved and started to be used in practical applications. On the other hand, pure blue phosphorescent material with long lifetime has not yet been found. Therefore the improvement of fluorescent pure blue performance has been continuously needed. In 2008, we developed a technology to enhance the efficiency of blue fluorescence, "Triplet-triplet fusion (TTF)", however the efficiency was not so high under 10% of EQE [1].Recently molecular orientation attracts much attention to promote high efficiency of OLED. Specific molecular structures which show horizontal orientation to a substrate has been reported [2]. In addition, specific host and dopant materials show molecular orientation in a blue fluorescence device and show high EQE in doped and un-doped emitting systems [3][4][5].The objective of this paper is to reveal the relationship between molecular orientation property of applicative fluorescent blue dopants (BDs) and EQE of OLEDs. We composed four kinds of different fluorescent blue dopants with different molecular shape (ovality) and examined the influence of molecular orientation of BDs on the efficiency improvement of OLEDs. We found that BDs with larger ovality bring larger orientation factor and higher EQE in blue OLEDs with "Efficiency enhancement layer (EEL)" to enhance TTF phenomenon. Furthermore, as a result of analyzing IVL characteristic, impedance spectroscopy and transient EL [6][7][8], it was clarified that the effect of the EQE improvement depends only on the orientation of BD because they showed almost same carrier balance and TTF efficiency.

We developed new fluorescent blue dopants (BDs) for achieving high-efficient blue organic light-emitting diode. A new BD showed both high photoluminescent quantum yield >0.9 and highly horizontal orientation (S 0 > 0.9) in doped film with keeping a chemical stability by introducing suitable substituents. We developed hole transporting materials and optimized the combination of hole transporting layers to decrease a carrier accumulation at the interface between electron blocking layer and emission layer. We found that the external quantum efficiency dependency from low to high current density was turned flat by promoting hole injection into emission layer. The top-emission organic lightemitting diode using the new BD and the optimized device architecture exhibited high efficiency of L/J/ CIEy around 200 at CIEy = 0.043.

A blue dopant (BD) emitting pure blue fluorescence was created on new design strategies that combined specific partial molecular structures to reduce peak shoulder of the fluorescence spectrum. The top emission organic light emitting diode using the new BD achieved L/J/CIEy=201, which was about 10% higher than the conventional BD.

New fluorescence blue host (BH) materials for achieving low voltage have been developed. Low efficiency and short lifetime were main issues to reduce operation voltage when using former generation blue hosts. Therefore new molecular structure of BH was designed to improve both electron and hole mobility and optimize ionization potential (IP) for overcoming the issues. New BHs showed lower voltage and comparable lifetime than former generation BHs. Furthermore, as a result of device optimization using the new BH, low voltage of 3.0V with a high current efficiency of 7.23cd/A, CIE-y of 0.053 at 10mA/cm 2 was successfully achieved in a top-emission device.

We developed new fluorescent blue dopants (BDs) for achieving high efficient blue organic light emitting diode (OLED). The new BD showed both high photoluminescent quantum yield >0.9 and highly horizontal orientation (S'>0.9) in the doped film with keeping a chemical stability by introducing suitable substituents. We developed hole transporting materials and optimized the combination of hole transporting layers to decrease a carrier accumulation at the interface between electron blocking layer/emission layer (EML). We found that the external quantum efficiency dependency from low to high current density was turned flat by promoting hole injection into EML. The Top Emission OLED using the new BD and the optimized device architecture exhibited high efficiency of L/J/CIEy around 200 at CIEy=0.043.