Improved efficiency of red phosphorescent organic light-emitting diodes with combination of heterojunction and mixed host structure

Dong Hwan Lim, Seok Jae Lee, Ja Ryong Koo, Bo Young Kim, Hyun Su Shin, Kum Hee Lee, Sang Youn Lee, Woo Young Kim, Seung Soo Yoon, Young Kwan Kim
Journal of Nanoscience and Nanotechnology 2014, 14 (8): 5998-6001
We report an improvement of efficiency in red phosphorescent organic light-emitting diodes (PHOLEDs) based on a combination of heterojunction (HJ) structure and mixed host (MH) system using a phosphorescent red emitter: bis(2-phenylquinolinato)-acetylacetonate iridium III [Ir(pq)2(acac)] doped in 4,4,N,N'-dicarbazolebiphenyl (CBP) of hole transport type host material and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) of electron transport type host material. This combination device resulted in an effective electron and hole balance and distribution of the recombination zone. Therefore, highly efficient red PHOLEDs with maximum luminous efficiency and external quantum efficiency of 21.93 cd/A and 14.09% were achieved. Moreover, the combination device showed a power efficiency of 9.51 lm/W, which is higher than 7.61 lm/W in the control device at a luminance of 1000 cd/m2.

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