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14 January 2008 Host engineering for high efficiency in phosphorescent organic light emitting diodes
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Device performances of green phosphorescent organic light-emitting diodes with triplet mixed host emitting layer were correlated with energy levels and composition of host materials. Two hole transport type host materials, (4,4'-N,N'- dicarbazole)biphenyl(CBP) and 4,4',4"-tris(N-carbazolyl)triphenylamine(TCTA), were combined with two electron transport type host materials, 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene(TPBI) and PH1. Maximum quantum efficiency was obtained in 5:5 mixed host in the case of TCTA:TPBI and TCTA:PH1, while CBP:PH1 showed the best performances in 9:1 mixed host. Quantum efficiency of green mixed host devices could be improved by more than 50 % compared with that of corresponding single host devices. Effect of dopant energy levels on device performances of triplet mixed host devices was also investigated and optimum composition for high efficiency depended on energy levels on dopant materials.
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Sung Hyun Kim, Kyoung Soo Yook, and Jun Yeob Lee "Host engineering for high efficiency in phosphorescent organic light emitting diodes", Proc. SPIE 6828, Light-Emitting Diode Materials and Devices II, 68280M (14 January 2008);


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