High efficiency phosphorescent blue organic light-emitting diode (OLED) was obtained by incorporating small amino or hydroxyl functional group-modified polymeric nano-dot (APND or HPND) in the hole transporting layer (HTL), poly (ethylenedioxythiophene): poly (styrene sulfonic acid) (PEDOT:PSS). The device comprised a 1250 (A) anode layer of indium tin oxide, a 350 (A) HTL of PEDOT:PSS doped with APND or HPND, a 400 (A) blue emissive layer com-posed of a molecular host of 4,4-bis (carbazol-9-yl) biphenyl doped with 14 wt％ blue dye of bis (3,5-difluoro-2-(2-pyridyl)-phenyl-(2-carboxypyridyl) iridium (III), a 320 (A) electron-transporting layer of 2, 2, 2-(1, 3, 5-benzenetriyl)-tris (1-phenyl-1-H-benzimidazole), a 7 (A) electron-injection layer of lithium fluoride and a 1500 (A) cathode layer of aluminum. The resultant power effi-ciency at 100 cd/m2, for example, was increased from 12.0 to 25.9 lm/W, an increase of 116％, as 7 wt％ APND of 8nm in size was added. By employing 7 wt％ HPND, the power-efficiency was 21.7 lm/W. The resultant luminance markedly increased with the incorporation of the PND. Whilst, the corresponding current density continuously decreased. These results indicate that the marked efficiency improvement may be attributed to a better balance of carrier-injection resulted from the hole-blocking-function possessed APND and the hole-trapping-function possessed HPND, which respectively exhibited positive and negative charge on the surface. Moreover, the chromaticity coordinate at 100 cd/m2, for example, was (0.19, 0.34), barely changed in the presence of the nano-dots. Importantly, since the nano-dot was not employed in the emissive layer, the same concept may be applied to fluorescent blue or other OLEDs.
Jwo-Huei Jou Chung-Che Chiang He Wang Wei-Ben Wang Mao-Feng Hsu Chi-Ping Liu Cheng-Chung Chen Chun-Jan Wang Yung-Cheng Tsai Jing-Jong Shyue Sung-Cheng Hu
Department of Materials Science and Engineering,National Tsing Hua University Hsin-Chu,Taiwan 30013, Department of Applied Chemistry,National Chi Nan University Nantou Hsien,Taiwan 545,China Department of Materials Science and Engineering,Tsinghua University Beijing 100084,China Research Center for Applied Sciences Academia Sinica 128 Academia Rd.,Sec.2 Nankang,Taipei 115,Taiwa Chung-shan Institute of Scince and Technology,Armament Bureau,M.N.D.No.481,Sec.Chia An,Zhongzheng Rd