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In this paper, efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable spectra are fabricated based on doping-free ultrathin emissive layers and mixed bipolar interlayers. To achieve WOLEDs, at least three kinds of light-emitting layers, i.e. blue, green and red, are needed. The traditional method to fabricate emissive layers is by co-evaporation, which can improve electroluminescent efficiency. However, the co-evaporation rate and dopant concentration are difficult to control, which leads to a bad reproducibility and thus goes against commercialization. In order to simplify the structures of WOLEDs and improve repeatability, several doping-free ultrathin emissive layers are used in this paper with 3 nm mixed bipolar interlayers separating them. The optimal ratio of bipolar hybrid material is determined by hole-only device, electron-only device and blue phosphorescent OLED. In addition, green, orange and red monochromatic OLED have also been fabricated separately, which are used to prove that mixed bipolar material is also suitable for the three phosphorescent emitting material. The WOLED with TCTA interlayers is fabricated to confirm that mixed bipolar material is beneficial to the characteristics of WOLEDs. The energy transfer process between different emitting materials is verified by studying the transient photoluminescence lifetime. The maximum efficiency of three-color and four-color doping-free WOLED are 52 cd/A (53.5 lm/W) and 13.8 cd/A (13.6 lm/W), respectively, and the maximum external quantum efficiency of three-color and four-color doping-free WOLED are 17.1% and 11.2%, respectively. Due to the sequential energy transfer structure between different emitting layers, the Commission Internationale de L'Eclairage coordinates shows a very slight variation of (0.005, 0.001) from 465 cd/m2 to 15950 cd/m2 for three-color WOLED. The Commission Internationale de L'Eclairage coordinates shows a variation of (0.023, 0.012) from 5077 cd/m2 to 14390 cd/m2 for four-color WOLED. The four-color WOLED shows a maximum color rendering index of 92.7 at 884 cd/m2, and it reaches 88.5 at 14390 cd/m2. In addition, the lifetime of phosphorescent OLED is usually poor due to the trap formed by triplet-polaron annihilation. The exciton distribution can be broadened and the exciton concentration can be reduced by using ultrathin light emitting layers (< 1 nm) and mixed bipolar interlayers. Therefore, triplet-polaron annihilation will be reduced, and the lifetime of OLEDs will be improved.
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Keywords:
- white organic light-emitting diodes /
- doping-free /
- bipolar hybrid interlayer /
- ultrathin emitting layer
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[19] Liu B Q, Nie H, Zhou X B, Hu S B, Luo D X, Gao D Y, Zou J H, Xu M, Wang L, Zhao Z J, Qin A J, Peng J B, Ning H L, Cao Y, Tang B Z 2016 Adv. Funct. Mater. 26 776
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[25] Yeh S J, Wu M F, Chen C T, Song Y H, Chi Y, Ho M H, Hsu S F, Chen C H 2005 Adv. Mater. 17 285
[26] Tokito S, Iijima T, Suzuri Y, Kita H, Tsuzuki T, Sato F 2003 Appl. Phys. Lett. 83 569
[27] Brunner K, Dijken A, Borner H, Bastiaanesen J J A M, Kiggen N M M, Langeveld B M W 2004 J. Am. Chem. Soc. 126 6035
[28] Thoms T, Okada S, Chen J P, Furugori M 2003 Thin Solid Films 436 264
[29] Tsuji T, Naka S, Okada H, Onnagawa H 2002 Appl. Phys. Lett. 81 3329
[30] Lee M T, Chu M T, Lin J S, Tseng M R 2010 J. Phys. D: Appl. Phys. 43 442003
[31] Yin Y M, Yu J, Cao H T, Zhang L T, Sun H Z, Xie W F 2014 Sci. Rep. 4 6754
[32] Zhao Y B, Chen J S, Ma D G 2013 ACS Appl. Mater. Interfaces 5 965
[33] Luo D X, Xiao Y, Hao M M, Zhao Y, Yang Y B, Gao Y, Liu B Q 2017 Appl. Phys. Lett. 110 061105
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[35] Xue K W, Sheng R, Duan Y, Chen P, Chen B Y, Wang X, Duan Y H, Zhao Y 2015 Org. Electron. 26 451
[36] Liu B Q, Nie H, Lin G W, Hu S B, Gao D Y, Zou J H, Xu M, Wang L, Zhao Z J, Ning H L, Peng J B, Cao Y, Tang B Z 2017 ACS Appl. Mater. Interfaces 9 34162
[37] Liu B Q, Tao H, Wang L, Gao D Y, Liu W C, Zou J H, Xu M, Ning H L, Peng J B, Cao Y 2016 Nano Energy 26 26
[38] Su S J, Gonmori E, Sasabe H, Kido J 2008 Adv. Mater. 20 4189
[39] Ding J Q, Wang Q, Zhao L, Ma D G, Wang L X, Jing X B, Wang F S 2010 J. Mater. Chem. 20 8126
[40] Su S J, Sasabe H, Takeda T, Kido J 2008 Chem. Mater. 20 1691
[41] Cai X Y, Padmaperuma A B, Sapochak L S, Vecchi P A, Burrows P E 2008 Appl. Phys. Lett. 92 083308
[42] Sun N, Wang Q, Zhao Y B, Chen Y H, Yang D Z, Zhao F C, Chen J S, Ma D G 2014 Adv. Mater. 26 1617
[43] Sun N, Wang Q, Zhao Y B, Yang D Z, Zhao F C, Chen J S, Ma D G 2014 J. Mater. Chem. C 2 7494
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[45] Lee J, Lee J I, Lee J Y, Chu H Y 2009 Appl. Phys. Lett. 95 253304
[46] Chen Y H, Chen J S, Zhao Y B, Ma D G 2012 Appl. Phys. Lett. 100 213301
[47] Chen P, Chen B Y, Zuo L M, Duan Y, Han G G, Sheng R, Xue K W, Zhao Y 2016 Org. Electron. 31 136
[48] Xie G H, Meng Y L, Wu F M, Tao C, Zhang D D, Liu M J, Xue Q, Chen W, Zhao Y 2008 Appl. Phys. Lett. 92 093305
[49] Jeon S O, Yook K S, Joo C W, Lee J Y 2010 Org. Electron. 11 881
[50] Kang J W, Lee S H, Park H D, Jeong W I, Yoo K M, Park Y S, Kim J J 2007 Appl. Phys. Lett. 90 223508
[51] Yu H J, Dai X D, Yao F N, Wei X, Cao J, Jhun C 2018 Sci. Rep. 8 6068
[52] Schwartz G, Pfeiffer M, Reineke S, Walzer K, Leo K 2007 Adv. Mater. 19 3672
[53] Zhao Y B, Zhu L P, Chen J S, Ma D G 2012 Org. Electron. 13 1340
[54] Zhu L P, Zhao Y B, Zhang H M, Chen J S, Ma D G 2014 J. Appl. Phys. 115 244512
[55] Zhang Y F, Lee J, Forrest S R 2014 Nat. Commun. 5 5008
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[1] Reineke S, Lindner F, Schwartz G, Seidler N, Walzer K, Lussem B, Leo K 2009 Nature 459 234
[2] D'Andrade B W, Forrest S R 2004 Adv. Mater. 16 1585
[3] Yang X L, Zhou G J, Wong W Y 2015 Chem. Soc. Rev. 44 8484
[4] Fan C, Yang C L 2014 Chem. Soc. Rev. 43 6439
[5] Sasabe H, Kido J 2013 J. Mater. Chem. 1 1699
[6] So F, Kondakov D 2010 Adv. Mater. 22 3762
[7] Wang Q, Ma D G 2010 Chem. Soc. Rev. 39 2387
[8] Wang Q, Ding J Q, Ma D G, Cheng Y X, Wang L X, Jing X B, Wang F S 2009 Adv. Funct. Mater. 19 84
[9] D'Andrade B W, Holmes R J, Forrest S R 2004 Adv. Mater. 16 624
[10] Sun Y, Forrest S R 2007 Appl. Phys. Lett. 91 263503
[11] Wang Q, Ding J Q, Ma D G, Cheng Y X, Wang L X, Wang F S 2009 Adv. Mater. 21 2397
[12] D'Andrade B W, Thompson M E, Forrest S R 2002 Adv. Mater. 14 147
[13] Shih P I, Shu C F, Tung Y L, Chi Y 2006 Appl. Phys. Lett. 88 251110
[14] Liu B Q, Wang L, Gao D Y, Xu M, Zhu X H, Zou J H, Lan L F, Ning H L, Peng J B, Cao Y 2015 Mater. Horiz. 2 536
[15] Liu B Q, Li X L, Tao H, Zou J H, Xu M, Wang L, Peng J B, Cao Y 2017 J. Mater. Chem. C 5 7668
[16] Sun Y R, Giebink N C, Kanno H, Ma B W, Thompson M E, Forrest S R 2006 Nature 440 908
[17] Tokito S, Iijima T, Tsuzuki T, Sato F 2003 Appl. Phys. Lett. 83 2459
[18] Liu B Q, Wang L, Gao D Y, Zou J H, Ning H L, Peng J B, Cao Y 2016 Light: Science & Applications 5 e16137
[19] Liu B Q, Nie H, Zhou X B, Hu S B, Luo D X, Gao D Y, Zou J H, Xu M, Wang L, Zhao Z J, Qin A J, Peng J B, Ning H L, Cao Y, Tang B Z 2016 Adv. Funct. Mater. 26 776
[20] Liu B Q, Wang L, Xu M, Tao H, Zou J H, Gao D Y, Lan L F, Ning H L, Peng J B, Cao Y 2014 Sci. Rep. 4 7198
[21] Ding L, Sun Y Q, Chen H, Zu F S, Wang Z K, Liao L S 2014 J. Mater. Chem. C 2 10403
[22] Liu B Q, Wang L, Tao H, Xu M, Zou J H, Ning H L, Peng J B, Cao Y 2017 Sci. Bull. 62 1193
[23] Lee C W, Lee J Y 2013 Adv. Mater. 25 596
[24] Holmes R J, Forrest S R, Tung Y J, Kwong R C, Brown J J, Garon S, Thompson M E 2003 Appl. Phys. Lett. 82 2422
[25] Yeh S J, Wu M F, Chen C T, Song Y H, Chi Y, Ho M H, Hsu S F, Chen C H 2005 Adv. Mater. 17 285
[26] Tokito S, Iijima T, Suzuri Y, Kita H, Tsuzuki T, Sato F 2003 Appl. Phys. Lett. 83 569
[27] Brunner K, Dijken A, Borner H, Bastiaanesen J J A M, Kiggen N M M, Langeveld B M W 2004 J. Am. Chem. Soc. 126 6035
[28] Thoms T, Okada S, Chen J P, Furugori M 2003 Thin Solid Films 436 264
[29] Tsuji T, Naka S, Okada H, Onnagawa H 2002 Appl. Phys. Lett. 81 3329
[30] Lee M T, Chu M T, Lin J S, Tseng M R 2010 J. Phys. D: Appl. Phys. 43 442003
[31] Yin Y M, Yu J, Cao H T, Zhang L T, Sun H Z, Xie W F 2014 Sci. Rep. 4 6754
[32] Zhao Y B, Chen J S, Ma D G 2013 ACS Appl. Mater. Interfaces 5 965
[33] Luo D X, Xiao Y, Hao M M, Zhao Y, Yang Y B, Gao Y, Liu B Q 2017 Appl. Phys. Lett. 110 061105
[34] Luo D X, Li X L, Zhao Y, Gao Y, Liu B Q 2017 ACS Photon. 4 1566
[35] Xue K W, Sheng R, Duan Y, Chen P, Chen B Y, Wang X, Duan Y H, Zhao Y 2015 Org. Electron. 26 451
[36] Liu B Q, Nie H, Lin G W, Hu S B, Gao D Y, Zou J H, Xu M, Wang L, Zhao Z J, Ning H L, Peng J B, Cao Y, Tang B Z 2017 ACS Appl. Mater. Interfaces 9 34162
[37] Liu B Q, Tao H, Wang L, Gao D Y, Liu W C, Zou J H, Xu M, Ning H L, Peng J B, Cao Y 2016 Nano Energy 26 26
[38] Su S J, Gonmori E, Sasabe H, Kido J 2008 Adv. Mater. 20 4189
[39] Ding J Q, Wang Q, Zhao L, Ma D G, Wang L X, Jing X B, Wang F S 2010 J. Mater. Chem. 20 8126
[40] Su S J, Sasabe H, Takeda T, Kido J 2008 Chem. Mater. 20 1691
[41] Cai X Y, Padmaperuma A B, Sapochak L S, Vecchi P A, Burrows P E 2008 Appl. Phys. Lett. 92 083308
[42] Sun N, Wang Q, Zhao Y B, Chen Y H, Yang D Z, Zhao F C, Chen J S, Ma D G 2014 Adv. Mater. 26 1617
[43] Sun N, Wang Q, Zhao Y B, Yang D Z, Zhao F C, Chen J S, Ma D G 2014 J. Mater. Chem. C 2 7494
[44] Marina E K, Thomas D P, Ralph H Y, David J G, Denis Y K, Christopher T B, Joseph C D, Jerome R L, Kevin P K 2008 J. Appl. Phys. 104 094501
[45] Lee J, Lee J I, Lee J Y, Chu H Y 2009 Appl. Phys. Lett. 95 253304
[46] Chen Y H, Chen J S, Zhao Y B, Ma D G 2012 Appl. Phys. Lett. 100 213301
[47] Chen P, Chen B Y, Zuo L M, Duan Y, Han G G, Sheng R, Xue K W, Zhao Y 2016 Org. Electron. 31 136
[48] Xie G H, Meng Y L, Wu F M, Tao C, Zhang D D, Liu M J, Xue Q, Chen W, Zhao Y 2008 Appl. Phys. Lett. 92 093305
[49] Jeon S O, Yook K S, Joo C W, Lee J Y 2010 Org. Electron. 11 881
[50] Kang J W, Lee S H, Park H D, Jeong W I, Yoo K M, Park Y S, Kim J J 2007 Appl. Phys. Lett. 90 223508
[51] Yu H J, Dai X D, Yao F N, Wei X, Cao J, Jhun C 2018 Sci. Rep. 8 6068
[52] Schwartz G, Pfeiffer M, Reineke S, Walzer K, Leo K 2007 Adv. Mater. 19 3672
[53] Zhao Y B, Zhu L P, Chen J S, Ma D G 2012 Org. Electron. 13 1340
[54] Zhu L P, Zhao Y B, Zhang H M, Chen J S, Ma D G 2014 J. Appl. Phys. 115 244512
[55] Zhang Y F, Lee J, Forrest S R 2014 Nat. Commun. 5 5008
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