A novel π-conjugated starburst molecule, 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), which forms a stable amorphous glass, functions as an excellent hole transport material for organic electroluminescent devices. An electroluminescent device consisting of double hole transport layers of m-MTDATA and 4,4′-bis(3-methylphenylphenylamino)biphenyl and an emitting layer of tris(8-quinolinolato)aluminum exhibits a high luminance efficiency and significant durability.

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Multilayer organic light-emitting device with phosphorescent guest emitter, tris(2-phenylpyridine)iridium (Ir(ppy)) doped in a host 4,4'-N,N'-dicarbazol-biphenyl (CBP) layer, exhibited very high luminous efficiency. A device having such phosphorescent guest emitter could not offer sufficiently long driving lifetime required by real products. On the other hand, phosphorescence in organic molecules rarely occurs at room temperature. We studied ways to increase driving lifetime by three types of experiments. First, we investigated to see whether the driving lifetime is dependent on guest molecule concentration. Second, we inserted Copper phtalocyanine (CuPc) between Indium Tin Oxide (ITO) anode and hole transport layer, 4,4'-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (NPB) to prevent driving voltage from rising during constant current operation. Finally, we exchanged the hole blocking layer, which is 2,9-dimethyl-4,7-diphenyl-1,1O-phenanthroline (BCP), for ((1 ,1 '-biphenyl)-4-olato)bis(2-methyl-8-quinolinolato N1,08)aluminum (BA1q). Optimizing all of the above mentioned steps, we can expect the half decay lifetime of 20000 hours or over at an initial luminance of lOOcd/m2 by constant current driving.

Abstract— A dot‐matrix display with 256 × 64 pixels with a pixel size of 0.34 × 0.30 mm in size, a luminance of 100 cd/m2, and a contrast ratio of 100:1 or better has been developed using organic LED devices. The display provides high luminance, high visibility, and wide viewing angle.

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