Properties of non-doped organic light-emitting devices based on an ultrathin iridium complex phosphor layer

Abstract

Organic light-emitting devices (OLEDs) were constructed with a structure of indium tin oxide (ITO)/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) (50-x nm)/bis[2-(4-tertbutylphenyl)benzothiazolato-N,C²′] iridium (acetylacetonate) [(t-bt)₂Ir(acac)] (d nm)/NPB (x nm)/2,2′,2′′(1,3,5-benzenetriyl)tris-(1-phenyl-1H-benzimidazole) (TPBI) (30 nm)/Mg:Ag (200 nm). A thin blue emission material of NPB was used as a separating layer, and the (t-bt)₂Ir(acac) yellow phosphorescent dye was acted as an ultrathin light-emitting layer. TPBI acted as both hole-blocking and electron-transporting layer. By changing the location (x) and the thickness (d) of the phosphor dye, the variation of device performance were investigated. The results showed that all the devices had a turn-on voltage of 2.8 V. In the case of d=0.2 nm and x=5 nm, the OLED had a maximum luminance of 18367 cd/m² and a maximum power efficiency of 5.3 lm/W. The high performance is attributed to both direct charge carrier trapping of iridium phosphor dye and the thin NPB separation layer, which effectively confines the recombination zone of charge carriers.

Keywords

organic light-emitting devices (OLEDs) / irid- ium complex phosphor dye / ultrathin layer / separation layer

References

[1] Reineke S, Lindner F, Schwartz G, Seidler N, Walzer K, Lüssem B, Leo K. White organic light-emitting diodes with fluorescent tube efficiency. Nature, 2009, 459(7244): 234–238

[2] Zhang D, Yang G, Wen W, Li L, Yu J, Jiang Q, Wang J, Zhong J, Zhu F, Luo K, Xie Y, Xu L. Study on electroluminescence characteristic of a new phosphorescent material. Journal of Optoelectronics Laser, 2009, 20(6): 754–757 (in Chinese)

[3] Wang Q, Ding J Q, Zhang Z Q, Ma D G, Cheng Y X, Wang L X, Wang F S. A high performance tandem white organic light-emitting diode combining highly effective white units and their interconnection layer. Journal of Applied Physics, 2009, 105(7): 076101

[4] Zhang C Y, Lu J B, Qin L, Hu H W, Kong L W. Design and fabrication of organic light-emitting white color micro-cavity device. Chinese Journal of Luminescence, 2009, 30(5): 596–600 (in Chinese)

[5] Kamtekar K T, Monkman A P, Bryce M R. Recent advances in white organic light-emitting materials and devices. Advanced Materials, 2009, 22(5): 572–582

[6] Lee S J, Park J S, Song M, Shin I A, Kim Y I, Lee J W, Kang J W, Gal Y S, Kang S, Lee J Y, Jung S H, Kim H S, Chae M Y, Jin S H. Synthesis and characterization of red-emitting iridium(III) complexes for solution-processable phosphorescent organic light-emitting diodes. Advanced Functional Materials, 2009, 19(14): 2205–2212

[7] Li L, Yu J S, Li Y, Jiang Y D. Luminescent properties of white organic light-emitting devices based on Rubrene ultrathin layer. Chemical Journal of Chinese Universities, 2009, 30(10): 2045–2048 (in Chinese)

[8] Deng Z R, Yang S Y, Meng L C, Lou Z D. Application of ultrathin layer in white organic electroluminescent devices. Acta Physico-Chimica Sinica, 2008, 24(4): 700–704 (in Chinese)

[9] Wang J, Yu J S, Li L, Wang T, Yuan K, Jiang Y D. Low roll-off power efficiency organic light-emitting diodes consisted of nondoped ultrathin phosphorescent layer. Applied Physics Letters, 2008, 92(13): 133308

[10] Cao J, Wei F X, Zhang X B, Jiang X Y, Zhang Z L, Zhu W Q, Xu S H. Enhances to efficiency of white organic light emitting diodes by introducing an exciton block layer. Journal of Optoelectronics Laser, 2005, 16(10): 1171–1174 (in Chinese)

[11] Ma H, Yip H L, Huang F, Jen A K Y. Interface engineering for organic electronics. Advanced Functional Materials, 2010, 20(9): 1371–1388

[12] Toshie T, Shigeki N, Hiroyuki O, Hiroyoshi O. Nondoped-type white organic electroluminescent devices utilizing complementary color and exciton diffuse. Applied Physics Letters, 2008, 81(18): 3329–3331

[13] Guo F W, Ma D G, Wang L X, Jing X, Wang F. High efficiency white organic light-emitting devices by effectively controlling exciton recombination region. Semiconductor Science and Technology, 2005, 20(3): 310–313

[14] Olthof S, Meerheim R, Schober M, Leo K. Energy level alignment at the interfaces in a multilayer organic light-emitting diode structure. Physical Review B, 2009, 79(24): 245308

[15] Marina E K, Joseph C D, Thomas D P, David J G, Denis Y K, Ralph H Y, Tommie L R, Dustin L C, Joel D S. Highly efficient fluorescent-phosphorescent triplet-harvesting hybrid organic light-emitting diodes. Journal of Applied Physics, 2010, 107(1): 014515

[16] Ji X Q, Li W Z, Zhong Z Y, Wang T, Jiang Y D. Study on the compound area of the blue OLED. Laser & optoelectronics progress, 2005, 42(7): 39–41 (in Chinese)

[17] Luo Y C, Hany Z. Correlation between triplet-triplet annihilation and electroluminescence efficiency in doped fluorescent organic light-emitting devices. Advanced Functional Materials, 2010, 20(8): 1285–1293

[18] Wang J, Jiang Y D, Yu J S, Lou S L, Lin H. Low operating voltage bright organic light-emitting diode using iridium complex doped in 4,4′-bis[N-1-napthyl-N-phenyl-amino]biphenyl. Applied Physics Letters, 2007, 91(13): 131105

[19] Li L, Yu J S, Wang J, Lou S, Jiang Y, Li W. High-efficiency white phosphorescent organic light-emitting diodes. Acta Physico-Chimica Sinica, 2007, 23(10): 1493–1497 (in Chinese)

Acknowledgements

This work was partially supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 60736005 and 60425101-1), the Foundation for Innovative Research Groups of the NSFC (No. 60721001), the Provincial Program (Nos. 9140A02060609DZ0208 and 20090185110020), the Program for New Century Excellent Talents in University (No. NCET-06-0812), the High Technology Research and Development Program of China (No. 2007AA03Z424), the Project Sponsored by SRF for ROCS, SEM (No. GGRYJJ08-05), and the Young Excellence Project of Sichuan (No. 09ZQ026-074).

RIGHTS & PERMISSIONS

2014 Higher Education Press and Springer-Verlag Berlin Heidelberg