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White organic light-emitting diodes (WOLEDs) have drawn considerable attention for next-generation lighting and display applications owing to their remarkable advantages. Phosphorescent OLED technology is crucial to realize high-efficiency white OLEDs because phosphorescent emitters enable to achieve almost 100% internal quantum efficiency (IQE) by harvesting all the excitons of 75% of triplets and 25% of singlets. However, an efficiency roll-off at high-brightness and a shift in color under various operation biases remains challenges. With the goal towards commercial applications, it requires WOLEDs should simultaneously realize high efficiency at high-brightness region over 1000 cd/m2 and good color stability over a wide electroluminescent range. In this paper, we first investigated the energy transfer process between the blue-emitting Bis (3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium (III) (Firpic) and the orange emitting Iridium (III) bis(4-(4-tert-butylphenyl)thieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01-TB), in addition to the behavior of the carrier trapping in the phosphorescent OLEDs with double emissive layers. Then we successfully fabricated phosphorescent WOLED with multiple emissive layers. The resulting phosphorescent WOLED achieves the maximum forward-viewing current efficiency (CE) of 34.6 cd/A and external quantum efficiency (EQE) of 13.5%, and the CE and the EQE remain 33.9 cd/A and 13.3% at 1000 cd/m2, respectively, indicating that the WOLED exhibits low efficiency roll-off. Furthermore, the WOLED shows very stable white emission with small Commission Internationale de L’Eclairage (CIE) coordinate varying range of (0.016, 0.011) from 1000 to 10000 cd/m2. The results provide a promising avenue to simultaneously achieve high efficiency, lower the efficiency roll-off at high brightness and color-stability for phosphorescent WOLEDs by carefully designing the device architecture to redistribute the charge carriers and excitons in the recombination zone.
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Keywords:
- white organic light-emitting diodes /
- efficiency roll-off /
- color-stability /
- phosphorescence
[1] Kido J, Hongawa K, Okuyama K, Nagai K 1994 Appl. Phys. Lett. 64 815Google Scholar
[2] Liu Y C, Li C S, Ren Z J, Yan S K, Bryce M R 2018 Nat. Rev. Mater. 3 18020Google Scholar
[3] Ai X, Evans E W, Dong S, Gillett A J, Guo H, Chen Y, Hele T J H, Friend R H, Li F 2018 Nature 563 536Google Scholar
[4] Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C 2012 Nature 492 234Google Scholar
[5] Reineke S, Lindner F, Schwartz G, Seidler N, Walzer K, Lüssem B, Leo K 2009 Nature 459 234Google Scholar
[6] Zhang X, Pan T, Zhang J, Zhang L, Liu S, Xie W 2019 ACS Photonics 6 2350Google Scholar
[7] Baldo M A, O'Brien D F, You Y, Shoustikov A, Sibley S, Thompson M E, Forrest S R 1998 Nature 395 151Google Scholar
[8] Zaen R, Park K M, Lee K H, Lee J Y, Kang Y J 2019 Adv. Opt. Mater. 190138 7
[9] Udagawa K, Sasabe H, Igarashi F, Kido J 2016 Adv. Opt. Mater. 4 86Google Scholar
[10] Liu D, Deng L J, Li W, Yao R J, Li D L, Wang M, Zhang S F 2016 Adv. Opt. Mater. 4 864Google Scholar
[11] Zhu L P, Wu Z B, Chen J S, Ma D G 2015 J. Mater. Chem. C 3 3304Google Scholar
[12] Lee C W, Lee J Y 2013 Adv. Mater. 25 5450Google Scholar
[13] Baldo M A, Adachi C, Forrest S R 2000 Phys. Rev. B 62 10967Google Scholar
[14] Reineke S, Walzer K, Leo K 2007 Phys. Rev. B 75 125328Google Scholar
[15] Giebink N C, Forrest S R 2008 Phys. Rev. B 77 235215Google Scholar
[16] Zhao C Y, Yan D H, Ahamad T, Alshehri S M, Ma D G 2019 J. Appl. Phys. 125 045501Google Scholar
[17] Yu Z W, Zhang J X, Liu S H, Zhang L T, Zhao Y, Zhao H Y, Xie W F 2019 ACS Appl. Mater. Interaces 11 6292Google Scholar
[18] Wang F, Zhao Y P, Xu H X, Zhang J, Miao Y Q, Guo K P, Shinar R, Shinar O S, Wang H, Xu B S 2019 Org. Electron. 70 272Google Scholar
[19] Maheshwaran A, Sree V G, Park H Y, Kim H, Han S H, Lee J Y, Jin S H 2018 Adv. Funct. Mater. 28 1802945Google Scholar
[20] Lee S, Kim K H, Limbach D, Park Y S, Kim J J 2013 Adv. Funct. Mater. 23 4105Google Scholar
[21] Gather M C, Alle R, Becker H, Meerholz K 2007 Adv. Mater. 19 4460Google Scholar
[22] Chen S F, Wu Q, Kong M, Zhao X F, Yu Z, Jia P P, Huang W 2013 J. Mater. Chem. C 1 3508Google Scholar
[23] Kim S H, Jang J, Lee J Y 2009 Synth. Met. 159 1295Google Scholar
[24] Liu B Q, Wang L, Xu M, Tao H, Xia X H, Zou J H, Su Y J, Gao D Y, Lan L F, Peng J J 2014 J. Mater. Chem. C 2 5870
[25] Ying S A, Xiao S, Yao J W, Sun Q, Dai Y F, Yang D Z, Qiao X F, Chen J S, Zhu T F, Ma D G 2019 Adv. Opt. Mater. 7 1901291Google Scholar
[26] 俞浩健, 姚方男, 代旭东, 曹进, 田哲圭 2019 物理学报 68 017202Google Scholar
Yu H J, Yao F N, Dai X D, Cao J, Jhun C 2019 Acta Phys. Sin. 68 017202Google Scholar
[27] Tanaka I, Tokito S 2004 Jpn. J. Appl. Phys. 43 7733Google Scholar
[28] Jou J H, Wang W B, Chen S Z, Shyue J J, Hsu M F, Lin C W, Shen S M, Wang C J, Liu C P, Chen C T, Wu M F, Liu S W 2010 J. Mater. Chem. 20 8411Google Scholar
[29] Su S J, Chiba T, Takeda T, Kido J 2008 Adv. Mater. 20 2125Google Scholar
[30] 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 1617Google Scholar
[31] Xu Z, Gong Y B, Dai Y F, Sun Q, Qiao X F, Yang D Z, Zhan X J, Li Z, Tang B Z, Ma D G 2019 Adv. Opt. Mater. 7 1801539Google Scholar
[32] Wu Z B, Wang Q, Yu L, Chen J S, Qiao X F, Ahamad T, Alshehri S M, Yang C L, Ma D G 2016 ACS Appl. Mater. Interfaces 8 28780Google Scholar
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图 8 白光器件W1和W2的 (a) 能级结构和发光层中激子复合过程示意图, 蓝色虚线框为载流子复合区, S1和S0分别代表单线态能级和基态(○), T1代表三线态能级(△); (b) 亮度-电压和关系特性曲线和归一化电致发光光谱(插图); (c) 电流效率-亮度-外量子效率关系特性曲线; (d) 器件B和W2的外量子效率-电流密度关系特性曲线, 图中红线和蓝线分别为的器件B和W2拟合曲线(TTA模型)
Figure 8. (a) Energy diagram and exciton dynamics of the WOLEDs W1 and W2. S1 and T1 are respectively the singlet (○) and triplet (△) energy levels, and S0 is the ground state (○). The blue dashed box depicts the main region of carrier recombination. Luminance-voltage characteristics and the normalized EL spectra (b), and current efficiency-Luminance-external quantum efficiency characteristics (c) of the WOLEDs W1 and W2; (d) EQE-current density of the OLEDs B and W2. The red and blue lines are corresponding fitting curves based on the TTA model, respectively.
表 1 器件A, B和器件W1, W2的电致发光性能参数
Table 1. EL performance parameters of the OLEDs in our studies.
Device Max EQE/CE/Luminance/
(%/[cd/A]/[cd/m2])At 1000 cd/m2 At 5000 cd/m2 EQE/CE/(%/[cd/A]) CIE/(x, y) CRI EQE/CE/(%/[cd/A]) CIE/(x, y) CRI A 7.3/16.5/8589 6.1/13.8 0.209, 0.351 44 4.2/9.6 0.215, 0.354 46 B 11.9/31.2/13890 11.7/30.8 0.303, 0.413 56 9.0/23.4 0.294, 0.408 56 W1 11.7/29.4/17260 11.4/28.3 0.320, 0.390 64 9.8/23.7 0.309, 0.383 65 W2 13.5/34.6/18340 13.3/33.9 0.342, 0.403 64 11.7/29.3 0.331, 0.395 65 -
[1] Kido J, Hongawa K, Okuyama K, Nagai K 1994 Appl. Phys. Lett. 64 815Google Scholar
[2] Liu Y C, Li C S, Ren Z J, Yan S K, Bryce M R 2018 Nat. Rev. Mater. 3 18020Google Scholar
[3] Ai X, Evans E W, Dong S, Gillett A J, Guo H, Chen Y, Hele T J H, Friend R H, Li F 2018 Nature 563 536Google Scholar
[4] Uoyama H, Goushi K, Shizu K, Nomura H, Adachi C 2012 Nature 492 234Google Scholar
[5] Reineke S, Lindner F, Schwartz G, Seidler N, Walzer K, Lüssem B, Leo K 2009 Nature 459 234Google Scholar
[6] Zhang X, Pan T, Zhang J, Zhang L, Liu S, Xie W 2019 ACS Photonics 6 2350Google Scholar
[7] Baldo M A, O'Brien D F, You Y, Shoustikov A, Sibley S, Thompson M E, Forrest S R 1998 Nature 395 151Google Scholar
[8] Zaen R, Park K M, Lee K H, Lee J Y, Kang Y J 2019 Adv. Opt. Mater. 190138 7
[9] Udagawa K, Sasabe H, Igarashi F, Kido J 2016 Adv. Opt. Mater. 4 86Google Scholar
[10] Liu D, Deng L J, Li W, Yao R J, Li D L, Wang M, Zhang S F 2016 Adv. Opt. Mater. 4 864Google Scholar
[11] Zhu L P, Wu Z B, Chen J S, Ma D G 2015 J. Mater. Chem. C 3 3304Google Scholar
[12] Lee C W, Lee J Y 2013 Adv. Mater. 25 5450Google Scholar
[13] Baldo M A, Adachi C, Forrest S R 2000 Phys. Rev. B 62 10967Google Scholar
[14] Reineke S, Walzer K, Leo K 2007 Phys. Rev. B 75 125328Google Scholar
[15] Giebink N C, Forrest S R 2008 Phys. Rev. B 77 235215Google Scholar
[16] Zhao C Y, Yan D H, Ahamad T, Alshehri S M, Ma D G 2019 J. Appl. Phys. 125 045501Google Scholar
[17] Yu Z W, Zhang J X, Liu S H, Zhang L T, Zhao Y, Zhao H Y, Xie W F 2019 ACS Appl. Mater. Interaces 11 6292Google Scholar
[18] Wang F, Zhao Y P, Xu H X, Zhang J, Miao Y Q, Guo K P, Shinar R, Shinar O S, Wang H, Xu B S 2019 Org. Electron. 70 272Google Scholar
[19] Maheshwaran A, Sree V G, Park H Y, Kim H, Han S H, Lee J Y, Jin S H 2018 Adv. Funct. Mater. 28 1802945Google Scholar
[20] Lee S, Kim K H, Limbach D, Park Y S, Kim J J 2013 Adv. Funct. Mater. 23 4105Google Scholar
[21] Gather M C, Alle R, Becker H, Meerholz K 2007 Adv. Mater. 19 4460Google Scholar
[22] Chen S F, Wu Q, Kong M, Zhao X F, Yu Z, Jia P P, Huang W 2013 J. Mater. Chem. C 1 3508Google Scholar
[23] Kim S H, Jang J, Lee J Y 2009 Synth. Met. 159 1295Google Scholar
[24] Liu B Q, Wang L, Xu M, Tao H, Xia X H, Zou J H, Su Y J, Gao D Y, Lan L F, Peng J J 2014 J. Mater. Chem. C 2 5870
[25] Ying S A, Xiao S, Yao J W, Sun Q, Dai Y F, Yang D Z, Qiao X F, Chen J S, Zhu T F, Ma D G 2019 Adv. Opt. Mater. 7 1901291Google Scholar
[26] 俞浩健, 姚方男, 代旭东, 曹进, 田哲圭 2019 物理学报 68 017202Google Scholar
Yu H J, Yao F N, Dai X D, Cao J, Jhun C 2019 Acta Phys. Sin. 68 017202Google Scholar
[27] Tanaka I, Tokito S 2004 Jpn. J. Appl. Phys. 43 7733Google Scholar
[28] Jou J H, Wang W B, Chen S Z, Shyue J J, Hsu M F, Lin C W, Shen S M, Wang C J, Liu C P, Chen C T, Wu M F, Liu S W 2010 J. Mater. Chem. 20 8411Google Scholar
[29] Su S J, Chiba T, Takeda T, Kido J 2008 Adv. Mater. 20 2125Google Scholar
[30] 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 1617Google Scholar
[31] Xu Z, Gong Y B, Dai Y F, Sun Q, Qiao X F, Yang D Z, Zhan X J, Li Z, Tang B Z, Ma D G 2019 Adv. Opt. Mater. 7 1801539Google Scholar
[32] Wu Z B, Wang Q, Yu L, Chen J S, Qiao X F, Ahamad T, Alshehri S M, Yang C L, Ma D G 2016 ACS Appl. Mater. Interfaces 8 28780Google Scholar
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