Sony has commercialized a full-color OLED comprising a new red emissive material, which provides high performance and long operation lifetime. We have carried out systematic research and developed a promising material that has excellent properties for practical applications. This compound shows an absorption peak and a luminescence peak at 483 nm and 644 nm, respectively. The molar absorption coefficient is large (ε = 38,100 M-1cm-1 in 1,4-dioxane) and the fluorescence quantum yield is also very high (QYf =0.82 in 1,4-dioxane). The glass transition temperature is as high as 135 °C. This compound offers thermally stable amorphous state in vacuum coating and is emissive even in single component films. We incorporated the new styryl compound in Sony's proprietary Super Top Emission technology and achieved outstanding brightness and wide color gamut comparable to the NTSC standard. The Super Top Emission consists of a top emitting device structure and color filters, which realize sufficient brightness and pure color at the same time without impairing the wide viewing angles. We obtained suitable device performance for practical use by tuning the layered structures. The emitting color is adjusted by optimizing the doping concentration of the styryl compound in the emitting layer and each thickness of the organic layers. We achieved the chromaticity (0.65, 0.35) in the CIE 1931 standard colorimetric system. The device operation lifetime exceeds 64,000 hours at the initial luminance 500 cd/m2. We would also like to discuss the advantages over the conventional red emissive materials.
We review our research activities in the field of organic light-emitting diodes (OLED's) aiming practical applications to full-color flat panel displays. The central issue of the research is to develop the suitable materials. The side-by- side patterning of discrete RGB sub-pixels without using dopants is straightforward and attractive from aspects of energy conversion efficiencies and productivity in comparison with the other methods proposed so far. We have been concerned in emitting material systems which emit R, G and B lights respectively using a common set of a hole-injecting layer, a hole-transporting layer (HTL), and electron transporting layer (ETL). Our research goal is to develop the good performance OLED matrices without using fluorescent dopants. Green light is obtained with an ordinary single hetero-structure. Blue light is achieved from the hole-transporting layer by inserting a hole-blocking layer between the HTL and the ETL. The maximum emission intensity was about 10,000 cd/m2 at the applied voltage of 9.5 V and the color was as good as (0.15, 0.16) in the CIE chromaticity coordinates. Our current research focuses on new red materials, which are suitable for the layered structures. These materials systems would provide full-color display panels with the minimum number of materials used.
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