磷光有機發光二極體(phosphorescent organic light-emitting diodes, PhOLEDs)由於可藉由單重態激子與三重態激子達到內部量子效率100%，在未來的平面顯示器與照明的應用上具有相當潛力。一般來說，為了促進元件載子平衡、增加電子與電洞於發光層再結合的機率，所使用的主體材料(host materials)通常具有電子傳輸能力以及電洞傳輸能力，而不同主體材料的設計會影響到電子與電洞再結合的比例(recombination ratio)。
本研究合成含有親電洞的三苯胺(triphenylamine)基團搭配不同比例親電子噁二唑(oxadiazole)基團結合之雙極主體材料(bipolar host materials)，命名為TPA-2OXD與TPA-3OXD。由於TPA-2OXD與TPA-3OXD的剛硬且非平面構形特性，其皆俱有高熱裂解溫度(>300 oC)與玻璃轉移溫度(>100 oC)，並且有均勻、穩定的成膜性質(RMS roughness< 1 nm)。在元件表現方面，利用濕式製程(solution process)分別以TPA-2OXD與TPA-3OXD混摻3 wt%綠色磷光材料Ir(ppy)3製作綠色磷光元件[ITO/PEDOT:PSS/host: 3 wt% Ir(ppy)3/BCP/LiF/Al]，元件最高亮度分別為8190 cd/m2、6299 cd/m2，最大電流效率分別為4.50 cd/A、1.53 cd/A，以TPA-2OXD 為主體材料時其元件性能較優，也比傳統的磷光主體材料PVK優，主要歸因於TPA-2OXD優秀的電子與電洞傳輸能力且載子較TPA-3OXD平衡，因此於發光層再結合的機率較高使得磷光元件的發光效率較佳。

Phosphorescent organic light-emitting diodes (PhOLEDs) offer a bright future for the next generation flat panel displays and lighting sources due to their high quantum efficiency through utilizing both singlet and triplet excitons to achieve the internal quantum efficiency of devices up to 100% theoretically. Generally, to facilitate balanced carrier recombination, host materials have to be capable of transporting both holes and electrons. However, the molecular design of the host materials affects the charge recombination zones.In this study, we designed and synthesized two host materials TPA-2OXD and TPA-3OXD composed of hole-transporting triphenylamino core linked with two and three electron-transporting aromatic 1,3,4-oxdiazolyl derivatives, respectively. They exhibited good thermal stability (Td > 300 oC, Tg > 100 oC) because of its rigid and non-planar structure. In addition, homogeneous films were readily obtained for both TPA-2OXD and TPA-3OXD by spin-coating process. Green PhOLEDs were successfully fabricated using Ir(ppy)3 as emitter [ITO/PEDOT:PSS/host+3 wt% Ir(ppy)3/BCP/LiF/Al]. The performances of TPA-2OXD-based device (maximum luminance: 8190 cd/m2, maximum current efficiency: 4.50 cd/A) were better than TPA-3OXD-based one (6299 cd/m2, 1.53 cd/A). This has been attributed to charge transport in TPA-2OXD is more balanced than TPA-3OXD that leads to higher recombination ratio. Moreover, the TPA-2OXD also excels conventional host-poly(N-vinylcarbazole) (PVK) in terms of device performance.

[1] M. Pope, P. Magnante, and H. P. Kallmann, J. Chem. Phys., vol. 38, p. 2042, 1963.
[2] C. W. Tang and S. A. Vanslyke, Appl. Phys. Lett., vol. 51, p. 913, 1987.
[3] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, et al., Nature, vol. 347, p. 539, 1990.
[4] 郭昭輝, PLED之發展技術, 塑膠資訊雜誌., 2002
[5] J. R. Lakowicz, Principles of Fluorescence Spectroscopy. 3rd ed.: Springer, 2006.
[6] D. A. Skoog, F. J. Holler, and S. R. Crouch, Principles of Instrumental Analysis. 6th ed, 2007.
[7] L. Akcelrud, Prog Polym Sci, vol. 28, p. 875, 2003.
[8] V. Tran and B. J. Schwartz, J Phys Chem B, vol. 103, p. 5570, 1999.
[9] J. E. Guillet, Polymer Photophysics and Photochemistry. New York: Canbridge University Press, 1985.
[10] H. H. Shih and C. H. Cheng, "Blue Phosphoresent Emitters and Hosts and Their Application in Organic and Their Application in Organic Electroluminescent Devices," Department of Chemistry, National Tsing Hua University, 2007.
[11] M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thomspon, S. R. Forrest, Nature, vol. 395, p. 151, 1998.
[12] N. J. Turro, Modern Molecular Photochemistry: University Science Book, CA, 1911.
[13] Z. H. Kafafi, Organic Electroluminescence, 2005.
[14] V. May and O. Kühn, Charge and Energy Transfer Dynamics in Molecular Systems. 2nd, rev. and enl. ed., 2004.
[15] M. A. Baldo, D. F. O'Brien, M. E. Thomspon, and S. R. Forrest, Phys. Rev. B, vol. 60, 1999.
[16] M. Wohlgenannt, K. Tandon, S. Mazumdar, S. Ramasesha, and Z. V. Vardeny, Nature, vol. 411, p. 617-617, 2001.
[17] M. Sudhakar, P. I. Djurovich, T. E. Hogen-Esch, and M. E. Thompson, J. Am. Chem. Soc, vol. 125, p. 7796, 2003.
[18] F. C. Chen, G. F. He, and Y. Yang, Apply. Phys. Lett, vol. 82, p. 1006, 2003.
[19] D. M. Pai, J. F. Yanus, and M. Stolka, J. Phys. Chem., vol. 88, p. 4717, 1984.
[20] X. Gong, M. R. Robinson, J. C. Ostrowski, D. Moses, G. C. Bazan, and A. J. Heeger, Adv. Mater, vol. 14, p. 581, 2001.
[21] P. I. Shih, C. H. Chien, F. I. Wu, and C. F. Shu, Adv. Funct. Mater, vol. 17, p. 3514, 2007.
[22] A. B. Padmaperuma, L. S. Sapochak, and P. E. Burrows, Chem. Mater., vol. 18, p. 2389, 2006.
[23] T. Tsuji, S. Kawami, T. Miyaguchi, T. Naijo, T. Yuki, S. Matsuo, H. Miyazaki, Proceedings of SID'04. Seattle, USA, 2004.
[24] Z. Ge, T. Hayakawa, S. Ando, M. Ueda, T. Akiike, H. Miyamoto, T. Kajita, M. A. Kakimoto, Adv. Funct. Mater, vol. 18, p. 584, 2008.
[25] Y. Tao, Q. Wang, C. Yang, Z. Zheng, T. Zou, J. Qin, et al., Angew. Chem. Int. Ed., vol. 47, p. 8104, 2008.
[26] Y. Tao, Q. Wang, C. Yang, C. Zhong, J. Qin, and D. Ma, Adv. Funct. Mater, vol. 20, p. 2923, 2010.
[27] T. Sajoto, P. I. Djurovich, A. Tamayo, M. Yousufuddin, R. Bau, M. E. Thompson, R. J. Holmes, S. R. Forrest, Inorganic Chemistry, vol. 44, p. 7992, 2005.
[28] N. Rehmann, D. Hertel, K. Meerholz, H. Becker, and S. Heun, Appl. Phys. Lett, vol. 91, p. 103507, 2007.
[29] X. Yang, D. Neher, D. Herte, and T. K. Doaubler, Adv. Mater, vol. 16, p. 161, 2004.
[30] T. Earmme, E. Ahmed, and S. A. Jenekhe, vol. 22, p. 4744, 2010.
[31] T. Earmme and S. A. Jenekhe, Adv. Funct. Mater, vol. 22, 2012.
[32] T. Earmme and S. A. Jenekhe, J. Mater. Chem, vol. 22, p. 4660, 2012.
[33] K. S. Yook and J. Y. Lee, Adv. Mater, 2014.
[34] C. Jiang, W. Yang, J. Peng, S. Xiao, and Y. Cao, Adv. Mater, vol. 16, p. 537, 2004.
[35] Y. C. Chen, G. S. Huang, C. C. Hsiao, and S. A. Chen, J. Am. Chem. Soc, vol. 128, p. 8549, 2006.
[36] H. Wu, G. Zhou, J. Zou, C. L. Ho, W. Y. Wong, W. Yang, J. Peng, Y. Cao, Adv. Mater, vol. 21, p. 4181, 2009.
[37] J. Lee, N. Chopra, S. H. Eom, Y. Zheng, and J. Xue, Appl. Phys. Lett, vol. 93, p. 123306, 2008.
[38] S. Lamansky, R. C. Kwong, M. Negent, P. I. Djurovich, and M. E. Thompson, Org. Electron, vol. 2, p. 53, 2001.
[39] S. Lamansky, P. I. Djurovich, F. Abdel-Razzaq, S. Garon, D. L. Murphy, and M. E. Thompson, Appl. Phys. Lett, vol. 92, p. 1570, 2002.
[40] B. Park, Y. H. Huh, H. G. Jeon, C. H. Park, T. K. Kang, B. H. Kim, et al., J. Appl. Phys., J. Park, vol. 108, p. 94506, 2010.
[41] Y.-T. Lee, Y.-T. Chang, M.-T. Lee, P.-H. Chiang, C.-T. Chen, and C.-T. Chen, J. Mater. Chem. C, vol. 2, p. 382, 2014.
[42] L. J. Deng, J. Y. Li, and W. Li, Dyes and Pigments, vol. 102, p. 150, 2014.
[43] Y. Shirota, K. Okumoto, and H. Inada, Synth. Met., vol. 111, p. 387, 2000.
[44] J. F. Rusling and S. L.Suib, Adv. Mater, vol. 6, 1994.
[45] M. H. Tasi, Y. H. Hong, C. H. Chang, H. C. Su, and C. C. Wu, Adv. Mater, vol. 19, p. 862, 2007.
[46] M. S. Lin, S. J. Yang, H. W. Chang, Y. H. Huang, Y. T. Tasi, and C. C. Wu, vol. 22, p. 16114, 2012.
[47] Y. Tao, Q. Wang, C. Yang, C. Zhong, K. Zhang, J. Qin, D. Ma, Adv. Funct. Mater, vol. 20, p. 304, 2010.
[48] L. Tao, J. Li, Y. Yu, Y. Jiang, C. S. Zhou, S. T. Lee, X. Zhang, O. Kwon, Chem. Mater., vol. 21, p. 1284, 2009.