臺灣博碩士論文加值系統

在本論文中，我們針對有機發光元件基礎特性到元件的製作進行研究。首先，我們利用頻譜阻抗技術研究摻雜了p型傳輸雜質的電洞傳輸層特性，並建構其等效電路。摻雜有傳輸雜質的電洞傳輸層，由於雜質分佈的影響，必須考量電極附近因能階差異額外形成的空乏區，以及會隨頻率變化的介電質響應，建構等效電路時也必須納入更為複雜的阻抗元件以達到更好的模擬結果。
接著我們試著對有機發光元件的結構做出簡化，利用兼具電洞和電子傳輸能力，並有著高三重階激發態能量的主發光體材料製作單層磷光有機發光元件，我們僅使用單一材料扮演電洞傳輸層、發光層以及電子傳輸層功能，大幅簡化了製作過程，並成功得到了高效率的單層藍光及白光磷光有機發光元件。
我們也以同一種主發光體材料，在僅使用額外各一層電洞及電子傳輸層的相對簡單結構下，實現了三層結構的高效率藍光及白光磷光有機發光元件，相對於現行常見的多層複雜結構，此一簡化的三層結構不僅有著高效率，而且由於主發光體兼具電洞和電子的傳輸特性，磷光元件在高亮度下常見的效率淬熄現象也大為減輕。
最後，我們利用新穎的藍光及紅光銥化合物，在適當的元件結構設計下，得到了適合白光照明應用，在不同照明亮度下皆具有良好演色能力的白光磷光發光元件。

In this dissertation, we studied fundamental properties and device architectures for organic light-emitting devices (OLEDs). First, the impedance spectroscopy was adopted to investigate the p-type conductively doped hole transporting layer and to construct equivalent circuits. Because of the addition of conductive dopant, it was found necessary to take account the difference between the bulk region and the depletion region near the electrode, and dispersion (i.e. frequency dependence) in the dielectric response of the conductively doped transport layer. As such, it is found necessary to include the non-conventional complex impedance element in the equivalent circuit to achieve tight matching of simulated results
The second part of the dissertation is about the simplification of OLED device structure. By the aid of the novel host material possessing bipolar transporting capability and high triplet energy, we successfully fabricated efficient single-layer phosphorescent OLEDs Efficient blue and white single-layer phosphorescent OLEDs were demonstrated.
Furthermore, we again adopted the same host material to fabricate conventional multi-layer OLEDs. With only adding a hole-transporting layer and an electron-transporting layer to form a relatively simple three-layer simple structure, very efficient blue and white phosphorescent OLEDs were implemented with small efficiency roll-off.
Finally, we utilized novel Ir-based blue and red phosphors to fabricated efficient white phosphorescent OLEDs (WOLEDs) for solid state lighting (SSL). With carefully designed device architectures, we achieved efficient phosphorescent WOLEDs with high color rendering index over a wide luminance range.

致謝 I
摘要 II
Abstract III
Contents V
Figure Contents VII
Table Contents XI

Chapter 1 Introduction 1
1.1 Overview of Organic Light-Emitting Devices 1
1.2 PIN OLEDs and Conductive Dopants 2
1.3 Single-layer OLEDs 4
1.4 Efficiency and Color Requirements in OLED Applications 5
1.5 Impedance Spectroscopy 14
1.6 Dissertation Organization 16
References 18

Chapter 2 Impedance Spectroscopy and Equivalent Circuits of Conductively Doped Organic Hole-Transport Materials 27
2.1 Introduction 27
2.2 Experimental Methods 28
2.3 Results and Discussion 30
2.4 Summary 40
References 41

Chapter 3 Efficient Single-Layer Phosphorescent Blue and White OLEDs Employing Large-Triplet-Energy and Ambipolar Host 60
3.1 Introduction 60
3.2 Experimental Methods 61
3.3 Blue- and White-Emitting Single-Layer Phosphorescent OLEDs 63
3.4 Summary 67
References 68

Chapter 4 Efficient Phosphorescent Blue and White OLEDs with Simple Device Architecture and Small Efficiency Roll-Off 80
4.1 Introduction 80
4.2 Experimental Methods 82
4.3 Efficient Blue Phosphorescent OLEDs with Simple Device Architecture and Small Efficiency Roll-off 84
4.4 Optimizing ITO Thickness for Enhancing Light Out-coupling of OLEDs 89
4.5 Efficient White Phosphorescent OLEDs with Simple Device Architecture and Small Efficiency Roll-off 91
4.6 Summary 92
References 94

Chapter 5 High Color-Rendering Phosphorescent White OLEDs Employing True-Blue and Large-Bandwidth Orange-Red Dopants 108
5.1 Introduction 108
5.2 Experimental Methods 108
5.3 Efficient White-Emitting Phosphorescent OLEDs with High Color Rendering Capability Using only Two Complementary Colors 111
5.4 Summary 116
References 118

Chapter 6 Summary 129

Chap. 1
[1]M. Pope, H. Kallmann, and P. Magnante, J. Chem. Phys. 38, 2042 (1963).
[2]W. Helfrich and W. G. Schneider, Phys. Rev. Lett. 14, 229 (1965).
[3]C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987).
[4]J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, K. Mackay, R. H. Friend, P. L. Burns, and A. B. Holmes, Nature 347, 539 (1990).
[5]C.-C. Wu, C.-W. Chen, C.-L. Lin, and C.-J. Yang, J. Disp. Technol. 1, 248 (2005).
[6]B. W. D’ Andrade and S. R. Forrest, Adv. Mater. 16, 1585 (2004).
[7]G. He, M. Pfeiffer, K. Leo, M. Hofmann, J. Birnstock, R. Pudzich, and J. Salbeck, Appl. Phys. Lett. 85, 3911 (2004).
[8]T. Y. Cho, C. L. Lin, and C. C. Wu, Appl. Phys. Lett. 88, 111106 (2006)
[9]J. Birnstock, T. Canzler, M. Hofmann, A. Lux, S. Murano, P. Wellmann, and A. Werner, J. Soc. Inf. Display 16, 221 (2008).
[10]M. Pfeiffer, K. Leo, X. Zhou, J. S. Huang, M. Hofmann, A. Werner, and J. Blochwitz-Nimoth, Org. Electron. 4, 89 (2003).
[11]K. Walzer, B. Maennig, M. Pfeiffer and K. Leo, Chem. Rev. 107, 1233 (2007).
[12]G. He, M. Pffeiffer, K. Leo, M. Hofmann, J. Birnstock, R. Pudzich, and J. Salbeck, Appl. Phys. Lett. 85, 3911 (2004).
[13]S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K.Walzer, B.Lussem, K. Leo, Nature 459, 234 (2009).
[14]J. Littman and P. Martic, J. Appl. Phys. 72, 1957 (1992).
[15]J. C. Ostrowski, M. R. Robinson, A. J. Heeger, and G. C. Bazan, Chem. Commun. 784 (2002).
[16]S. C. Tse, K. K. Tsung, and S. K. So, Appl. Phys. Lett. 90, 213502 (2007).
[17]V.-E. Choong, S. Shi, J. Curless, C.-L. Shieh, H.-C. Lee, F. So, J. Shen and J. Yang, Appl. Phys. Lett. 75, 172 (1999).
[18]W. Brutting, S. Berleb, and A. G. Muckl, Org. Electron. 2, 1 (2001).
[19]N. K. Patel, S. Cina, and J. H. Burroughes, IEEE J. Sel. Top. Quantum Electron. 8, 346 (2002).
[20]H. S. Nalwa and L. S. Rohwer. Handbook of Luminescence, Display Materials and Devices. Volume 1 Organic Light-Emitting Diodes, American Scientific Publisher (2003)
[21]N. C. Greenham, R. H. Friend, D. D. C. Bradley, Adv. Mater. 6, 491 (1994).
[22]J.-S. Kim, P. K. H. Ho, N. C. Greenham, R. H. Friend, J. Appl. Phys. 88, 1074 (2000).
[23]M.-H. Lu, J. C. Sturm, J. Appl. Phys. 91, 595 (2002).
[24]M. A. Baldo, D. F. O’Brien, M. E. Thompson, and S. R. Forrest, Phys. Rev. B 60, 14422 (1999).
[25]C. Adachi, M. A. Baldo, M. E. Thompson, and S. R. Forrest, J. Appl. Phys. 90, 5048 (2001).
[26]Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, and S. R. Forrest, Nature 440, 908 (2006).
[27]J. J. Shiang and A. R. Duggal, J. Appl. Phys. 95, 2880(2004).
[28]Y. S. Tyan, J. D. Shore, G. Farruggia, and T. R. Cushman, SID 05 DIGEST 142, 2005.
[29]C. F. Madigan, M. H. Lu, and J. C. Sturm, Appl. Phys. Lett. 76, 1650 (2000).
[30]Y. Sun and S. R. Forrest, Nature Photonics 2, 483 (2008).
[31]J. Kido, M. Kimura, and K. Nagai, Science 267 1332 (1995).
[32]Y. Sun and S. R. Forrest, Appl. Phys. Lett. 91, 263503 (2007).
[33]E. L. Williams, K. Haavisto, J. Li, and G.E. Jabbour, Adv. Mater. 19, 197 (2007).
[34]F. So, J. Kido, and P. Burrows, MRS Bulletin 33, 663 (2008).
[35]S. Tokito, T. Lijima, T. Tsuzuki, and F. Sato, Appl. Phys. Lett. 83, 2459 (2003).
[36]B. W. D’Andrade, R. J. Holmes, and S. R. Forrest, Adv. Mater. 16, 624 (2004).
[37]G. Wyszecki and W. S. Stiles, Color Science, John Wiley & Sons, 173 (2000).
[38]P. Chen, W. Xie, J. Li, T. Guan, Y. Duan, Y. Zhao, S. Liu, C. Ma, L. Zhang, and B. Lib, Appl. Phys. Lett. 91, 023505 (2007).
[39]C.-H. Chang, C.-C. Chen, C.-C. Wu, S.-Y. Chang, J.-Y. Hung, and Y. Chi, Org. Electron. 11, 266 (2010).
[40]H. Kanno, N. C. Giebink, Y. Sun, and S. R. Forrest, Appl. Phys. Lett. 89, 023503 (2006).
[41]G. Schwartz, S. Reineke, K. Walzer, and K. Leo, Appl. Phys. Lett. 92, 053311 (2008).
[42]G. Schwartz, M. Pfeiffer, S. Reineke, K. Walzer, and K. Leo, Adv. Mater. 19, 3672 (2007).
[43]C.-H. Chang, K.-C. Tien, C.-C. Chen, M.-S. Lin, H.-C. Cheng, S.-H. Liu, C.-C.Wu, J.-Y. Hung, Y.-C. Chiu, and Y. Chi, Org. Electron. 11, 412 (2010).
[44]J. R. MacDonald, Impedance Spectroscopy – Emphasizing Solid Materials and Systems, Wiley, New York (1987).
[45]H. C. F. Martens, H. B. Brom, and P. W. M. Blom, Phys. Rev. B 60, 8489 (1999).
[46]C. Jonda and A. B. R. Mayer, Chem. Mater. 11, 2429 (1999).

Chap 2

[1]C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987).
[2]J. R. Sheats, H. Antoniadis, M. Hueschen, W. Leonard, J. Miller, R. Moon, D. Roitman, and A. Stocking, Science 273, 884 (1996).
[3]M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, and S. R. Forrest, Nature 395, 151 (1998).
[4]Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, and S. R. Forrest, Nature 440, 908 (2006).
[5]S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K. Walzer, B. Lussem, and K. Leo, Nature 459, 234 (2009).
[6]J. Huang, M. Pfeiffer, A. Werner, J. Blochwitz, S. Liu, and K. Leo, Appl. Phys. Lett. 80, 139 (2002).
[7]C. L. Lin, T. Y. Cho, C. H Chang, and C. C. Wu, Appl. Phys. Lett. 88, 081114 (2006).
[8]T. Y. Cho, C. L. Lin, and C. C. Wu, Appl. Phys. Lett. 88, 111106 (2006)
[9]C. I. Wu, C. T. Lin, Y. H. Chen, M. H. Chen, Y. J. Lu, and C. C. Wu, Appl. Phys. Lett. 88, 152104 (2006).
[10]T. Matsushima and C. Adachi, Appl. Phys. Lett. 89, 253506 (2006).
[11]M. H. Ho, S. F. Hsu, J. W. Ma, S. W. Hwang, P. C. Yeh, and C. H. Chen, Appl. Phys. Lett. 91, 113518 (2007).
[12]K. Walzer, B. Maennig, M. Pfeiffer and K. Leo, Chem. Rev. 107, 1233 (2007)
[13]M. Meier, S. Karg, and W. Riess, J. Appl. Phys. 82, 1961 (1997).
[14]S. Berleb and W. Brutting, Phys. Rev. Lett. 89, 286601 (2002)
[15]J. Bisquert, G. Garcia-Belmonte, A. Pitarch, and H. J. Bolink, Chem. Phys. Lett. 422, 184 (2006).
[16]N. D. Nguyen, M. Schmeits, and H. P. Loebl, Phys. Rev. B 75, 075307 (2007).
[17]J. R. MacDonald, Impedance Spectroscopy – Emphasizing Solid Materials and Systems, Wiley, New York (1987).
[18]C. Jonda and A. B. R. Mayer, Chem. Mater. 11, 2429 (1999).
[19]L. S. C. Pingree, B. J. Scott, M. T. Russell, T. J. Marks, and M. C. Hersam, Appl. Phys. Lett. 86, 073509 (2005).
[20]Y. Shirota, Y. Kuwabara, H. Inada, T. Wakimoto, H. Nakada, Y. Yonemoto, S. Kawami, and K. Imai, Appl. Phys. Lett. 65, 807 (1994).
[21]J. Blochwitz, M. Pfeiffer, T. Fritz, and K. Leo, Appl. Phys. Lett. 73, 729 (1998).
[22]J. Drechsel, M. Pfeiffer, X. Zhou, A. Nollau, and K. Leo, Synth. Met. 127, 201 (2002).
[23]H. Gohr, J. Schaller, C.-A. Schiller, Electrochim. Acta 38,1961 (1993).
[24]A. K. Jonscher, Phys. Status Solidi A 32, 664 (1975).
[25]K. S. Cole and R. H. Cole, J. Chem. Phys. 9, 341 (1941)

Chap 3
[1]M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, M. E. Thompson, S. R. Forrest, Nature 395, 151 (1998).
[2]B. W. D’Andrade and S. R. Forrest, Adv. Mater. 16, 1585 (2004).
[3]S.-H. Eom, Y. Zheng, N. Chopra, J. Lee, F. So, J. Xue, Appl. Phys. Lett. 93, 133309 (2008).
[4]S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K.Walzer, B.Lussem, K. Leo, Nature 459, 234 (2009).
[5]J. Littman, P. Martic, J. Appl. Phys. 72, 1957 (1992).
[6]V. E. Choong, S. Shi, J. Curless, C.-L. Shieh, H.-C. Lee, F. So, J. Shen, J. Yang, Appl. Phys. Lett. 75, 172 (1999) .
[7]Z. Zhao, J.-H. Li, P. Lu, Y. Yang, Adv. Funct. Mater. 17, 2203 (2007).
[8]K. R. J. Thoms, M. Velusamy, J. T. Lin, Y.-T. Tao, C.-H. Chuen, Adv. Funct. Mater. 14, 387 (2004).
[9]T.-H. Huang, J. T. Lin, L.-Y. Chen, C.-C. Wu, Adv. Mater. 18, 602 (2006).
[10]M.-Y. Lai, C.-H. Chen, W.-S. Huang, J. T. Lin, T.-H. Ke, L.-Y. Chen, M.-H. Tsai, C.-C. Wu, Angew. Chem. Int. Ed. 47, 581 (2008).
[11]Doctoral Dissertation of Dr. Tung-Hui Ke, Graduate Institute of Photonics and Optoelectronics, National Taiwan University.
[12]Doctoral Dissertation of Dr. Ming-Han Tsai, Graduate Institute of Photonics and Optoelectronics, National Taiwan University.
[13]X. Gong, M. R. Robinson, J. C. Ostrowski, D. Moses, G. C. Bazan, A. J. Heeger, Adv. Mater. 14, 581 (2002).
[14]X. Yang, D. Neher, D. Hertel, T. K. Daubler, Adv. Mater. 16, 161 (2004).
[15]J. Huang, T. Watanabe, K. Ueno, Y. Yang, Adv. Mater. 19, 739 (2007).
[16]G. E. Jabbour, B. Kippelen, N. R. Armstrong, N. Peyghambarian, Appl. Phys. Lett. 73, 1185 (1998).
[17]S. Tokito, K. Noda, Y. Taga, J. Phys. D:Appl. Phys. 29, 2750 (1996).
[18]T. Matsushima, H. Murata, J. Appl. Phys. 104, 034507 (2008).
[19]J. Meyers, S. Hamwi, T. Bulow, H.-H. Johnannes, T. Ridei, W. Kowalsky, Appl. Phys. Lett. 91, 113506 (2007).
[20]M. A. Baldo, C. Adachi, S. R. Forrest, Phys. Rev. B 62, 10967 (2000).
[21]W. Staroske, M. Pfeiffer, K. Leo, Phys. Rev. Lett. 98, 197402 (2002) .
[22]S. Reineke, K. Walzer, K. Leo, Phys. Rev. B 75, 125328 (2007).
[23]C.-H. Chang, Y.-H. Lin, C.-C. Chen, C.-K. Chang, C.-C. Wu, L.-S. Chen, W.-W. Wu, Y. Chi. Org. Electron. 10, 1364 (2009).

Chap 4
[1]C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987).
[2]J. Kido, M. Kimura, and K. Nagai, Science 267, 1332 (1994).
[3]B. W. D’Andrade, R. J. Holmes, and S. R. Forrest, Adv. Mater. 16, 624 (2004).
[4]S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K.Walzer, B.Lussem, K. Leo, Nature 459, 234 (2009).
[5]C. Adachi, M. A. Baldo, M. E. Thompson, and S. R. Forrest, J. Appl. Phys. 90 5048 (2001).
[6]Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, and S. R. Forrest, Nature, 440, 908, (2006).
[7]N. K. Patel, S. Cina, and J. H. Burroughes, IEEE Journal of Selected Topics in Quantum Electronics/Journal of Display Technology, 8, 346 (2002).
[8]S. Tokito, T. Iijima, T. Tsuzuki, and F. Sato, Appl. Phys. Lett. 83, 2459 (2003).
[9]M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M .E. Thompson, and S. R. Forrest, Nature, 395, 151 (1998).
[10]C. Adachi, R. C. Kwong, P. Djurovich, V. Adamovich, M. A. Baldo, M. E. Thompson, and S. R. Forrest, Appl. Phys. Lett. 79, 2082 (2001).
[11]R. J. Holmes, S. R. Forrest, Y.-J. Tung, R. C. Kwong, J. J. Brown, S. Garon, and M. E. Thompson, Appl. Phys. Lett. 82, 2422, (2003).
[12]S. Tokito, T. Ijima, Y. Suzuri, H. Kita, T. Tsuzuki, and F. Sato, Appl. Phys. Lett. 83, 569 (2003).
[13]M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, and S. R. Forrest, Appl. Phys. Lett. 75, 4 (1999).
[14]C. Adachi, R. C. Kwong, P. Djurovich, V. Adamovich, M. A. Baldo, M. E. Thompson, and S. R. Forrest, Appl. Phys. Lett. 79, 2082 (2001).
[15]Doctoral Dissertation of Dr. Ming-Han Tsai, Graduate Institute of Photonics and Optoelectronics, National Taiwan University.
[16]Doctoral Dissertation of Dr. Tung-Hui Ke, Graduate Institute of Photonics and Optoelectronics, National Taiwan University.
[17]P. Strohriegl and J. V. Grazulevicius, Adv. Mater. 14, 1439, (2002).
[18]K. Goushi, R. Kwong, J. J. Brown, H. Sasabe, and C. Adachi, J. Appl. Phys. 95, 7798 (2004).
[19]Y. Zheng, S.-H. Eom, N. Chopra, J. Lee, F. So, and J. Xue, Appl. Phys. Lett. 92, 223301 (2008).
[20]S.-J. Su, T. Chiba, T. Takashi, and J. Kido, Adv. Mater. 20, 2125 (2008).
[21]S. Naka, H. Okada, H. Onnagawa, and T. Tsutsui, Appl. Phys. Lett. 76, 197 (2000).
[22]Q. Xin, W. L. Li, W. M. Su, T. L. Li, Z. S. Su, B. Chu, and B. Li, J. Appl. Phys. 101, 044512 (2007).
[23]D. Tanaka, T. Takeda, T. Chiba, S. Watanabe, and J. Kido, Chem. Lett. 36, 262 (2007).
[24]N. Chopra, J. Lee, Y. Zheng, S.-H. Eom, J. Xue, and F. So, Appl. Phys. Lett. 93, 143307 (2008).
[25]H. Sasabe, E. Gonmori, T. Chiba, Y.-J. Li, D. Tanaka, S.-J. Su, T. Takeda, Y.-J. Pu, K. Nakayama, and J. Kido, Chem. Mater. 20, 5951 (2008).
[26]L. Xiao, S.-J. Su, Y. Agata, H. Lan, and J. Kido, Adv. Mater. 21, 1271 (2009).
[27]N. Seidler, S. Reineke, K. Walzer, Bjorn Lussem, A. Tomkeviciene, J. V. Grazulevicius, and K. Leo, Appl. Phys. Lett. 96, 093304 (2010).
[28]R. G. Kepler, J. C. Caris, P. Avakian, and E. Abramson, Phys. Rev. Lett. 10, 400 (1963).
[29]S. Reineke, K. Walzer, and K. Leo, Phys. Rev. B 75, 125328 (2007).
[30]C. F. Madigan, M.-H. Lu and J. C. Sturm, Appl. Phys. Lett. 76, 1650 (2000).
[31]J. J. Shiang and A. R. Duggal, J. Appl. Phys. 95, 2880 (2004).
[32]Y.-S. Tyan, Y.-Q. Rao, X.-F. Ren, R. Kesel, T. R. Cushman, W. J. Begley, and N. Bhandari, SID 09 DIGEST 895 (2009).
[33]Y. Sun and S. R. Forrest, Nature Photonic 2,483 (2008).
[34]Y. S. Sung, Thin Solid Films 467, 36 (2004).
[35]C.-H. Chang, Y.-H. Lin, C.-C. Chen, C.-K. Chang, C.-C. Wu, L.-S. Chen, W.-W. Wu, Y. Chi. Org. Electron. 10, 1364 (2009).

Chap 5
[1]B. W. D’Andrade and S. R. Forrest, Adv. Mater. 16, 1585 (2004)
[2]F. So, J. Kido, and P. Burrows, MRS Bulletin 33, 663 (2008).
[3]J.-Y. Hung, Y. Chi, I.-H. Pai, Y.-C. Yu, G.-H. Lee, P.-T. Chou, K.-T. Wong, C.-C. Chen, and C.-C. Wu, Dalton Trans. 33, 6472 (2009).
[4]C.-H. Chang, C.-C. Chen, C.-C. Wu, C.-H. Yang, and Y. Chi, Org. Electronics 10, 1364 (2009).
[5]M.-H. Tsai, H.-W. Lin, H.-C. Su, C.-C. Wu, F.-C. Fang, Y.-L. Liao, K.-T. Wong, and C.-I. Wu, Adv. Mater. 18, 1216, (2006).
[6]R. J. Holmes, B. W. D’Andrade, S. R. Forrest, X. Ren, J. Li, and M. E. Thompson, Appl. Phys. Lett. 83, 3818, (2003).
[7]V. I. Adamovich, S. R. Cordero, P. I. Djurovich, A. Tamayo, M. E. Thompson, and B. W. DAndrade, Org. Electronics 4, 77 (2003).
[8]C.-I. Wu, C.-T. Lin, Y.-H. Chen, M.-H. Chen, Y.-J. Lu, and C.-C. Wu, Appl. Phys. Lett. 88,152104, (2006).
[9]M. A. Baldo, C. Adachi, and S. R. Forrest, Phys. Rev. B 62, 10967 (2000).
[10]S. Reineke, K. Walzer, and K. Leo, Phys. Rev. B 75, 125328 (2007).