English

Single-Layer Organic Light-Emitting Devices with C₆₀ and MoO₃ Mixed Materials as Hole Injection Layer

• XUE Kai ,
• YAN Minnan ,
• PAN Fei ,
• TIAN Mengying ,
• PAN Xudong ,
• ZHANG Hongmei ^,

• Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced Materials, Jiangsu National Synergistic Innovation Center for Advanced Materials, Nanjing University of Posts & Telecommunications, Nanjing 210023, P. R. China

Corresponding author: ZHANG Hongmei, Email: iamhmzhang@njupt.edu.cn; Tel.: +86-13372017090

• Received Date: 30 October 2018
  Accepted Date: 11 December 2018
  Revised Date: 10 December 2018
  Available Online: 15 August 2019
• Fund Project:

  The project was supported by the National Natural Science Foundation of China (61674081, 51333007)

Abstract: Multilayer phosphorescent organic lighting-emitting diodes (PHOLEDs) with complicated device configurations have greatly increased the complexity of manufacturing and the fabrication cost. Therefore, there is strong incentive to develop simplified OLEDs, such as a single-layer device that has the structure of anode/hole injection layer (HIL)/emissive layer/electron injection layer/cathode. However, because of the absence of a carrier transport layer, the single-layer device suffers from severe charge injection difficulties and unbalanced carrier transport. Hence, the performances of single-layer devices reported so far have not been satisfactory. It has been proved that the modification of the electrode/organic interface could influence carrier injection to improve the device performance in multilayer PHOLEDs. Modification of the electrode/organic interface is more essential for achieving high-performance single-layer OLEDs. In this work, efficient green phosphorescent single-layer OLEDs based on the structure of indium tin oxide (ITO)/C₆₀ (1.2 nm):MoO₃ (0.4 nm)/1, 3, 5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi):fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃]/LiF (0.7 nm)/Al (120 nm) were fabricated. C₆₀, MoO₃, and C₆₀:MoO₃ were applied as the HILs, respectively, for comparison. The layer of TPBi played a dual role of host and electron-transporting material within the emission layer. Thus, the properties of the HILs play an important role in the adjustment of electron/hole injection to attain transport balance of the charge carriers in single-layer OLEDs with electron-transporting hosts. It is found that appropriate adjustment of the HIL is a key factor to achieve high-efficiency single-layer OLEDs. The large affinity of MoO₃ (6.37 eV), inducing electron transfer from the highest occupied molecular orbital of C₆₀ to MoO₃, results in the formation of C₆₀ cations and induces the decrease of the valence from Mo⁺⁶ to Mo⁺⁵; therefore, C₆₀:MoO₃ can adjust the hole injection properties well. Finally, a single-layer OLED with a maximum current efficiency of 35.88 cd∙A⁻¹ was achieved. Compared with devices with MoO₃ (28.99 cd∙A⁻¹) or C₆₀ (10.46 cd∙A⁻¹) as HILs, the device performance was improved by 24% and 243%, respectively. Overall, a novel and effective method of using different mixed ratios of C₆₀ and MoO₃ as the HIL to realize effective charge carrier regulation is proposed, and it is of great significance for fabricating high-performance single-layer OLEDs.

Key words:
• Single-layer
•  /  Organic light-emitting diodes
•  /  Hole injection layer
•  /  Mixed materials
•  /  Balance of charge carriers

• 1. [1]

     Liu, Z. W.; Helander, M. G.; Wang, Z. B.; Lu, Z. H. Org. Electron. 2009, 10, 1146. doi: 10.1016/j.orgel.2009.06.002

  2. [2]

     Yin, Y. M.; Wen, X. M.; Yu, J.; Zhang, L.T.; Xie, W. F. IEEE Photonics Technol. Lett. 2013, 25, 2205. doi: 10.1109/LPT.2013.2283215

  3. [3]

     Liu, Z. W.; Helander, M. G.; Wang, Z. B.; Lu, Z. H. Org. Electron. 2013, 14, 852. doi: 10.1016/j.orgel.2013.01.009

  4. [4]

     Zeng, W. J.; Bi, R.; Zhang, H. M.; Huang, W. J. Appl. Phys. 2013, 116, 224502. doi: 10.1063/1.4903752

  5. [5]

     Zuo, L. M.; Han, G.G.; Sheng, R.; Xue, K. W.; Duan, Y.; Chen, P.; Zhao, Y. RSC Adv. 2016, 6, 55017. doi: 10.1039/c6ra07741b

  6. [6]

     Wu, Z. X.; Yang, Z. L.; Xue, K.; Fei, C. C.; Wang, F.; Yan, M. N.; Zhang, H. M.; Ma, D. G.; Huang, W. RSC Adv. 2018, 8, 11255. doi: 10.1039/c7ra13355c

  7. [7]

     Han, T. H.; Choi, M. R.; Woo, S. H.; Min, S. Y.; Lee, C. L.; Lee, T. W. Adv. Mater. 2012, 24, 1487. doi: 10.1002/adma.201104316

  8. [8]

     Han, T. H.; Kim, Y. H.; Kim, M. H.; Song, W.; Lee, T. W. ACS Appl. Mater. Interfaces 2016, 8, 6152. doi: 10.1021/acsami.5b11791

  9. [9]

     Wang, Y. P.; Wang, W. J.; Huang, Z. J.; Wang, H. H.; Zhao, J. T.; Yu, J. H.; Ma, D. G. J. Mater. Chem. C 2018, 6, 7042. doi: 10.1039/c8tc01639a

  10. [10]

      Miao, Y. Q.; Wang, K. X.; Gao, L.; Zhao, B.; Wang, H.; Zhu, F. R.; Xu, B. S.; Ma, D. G. J. Mater. Chem. C 2018, 6, 8122. doi: 10.1039/c8tc02479k

  11. [11]

      Zhang, T. M.; Shi, C. S.; Zhao, C. Y.; Wu, Z. B.; Chen, J. S.; Xie, Z. Y.; Ma, D. G. ACS Appl. Mater. Interfaces 2018, 10, 8148. doi: 10.1021/acsami.8b00513

  12. [12]

      Kim, D. H.; Lee, W. H.; Jesuraj, P. J.; Hafeez, H.; Lee, J. C.; Choi, D. K.; Song, A.; Chung, K. B.; Bae, T. S.; Song, M.; et al. Org. Electron. 2018, 61, 343. doi: 10.1016/j.orgel.2018.06.013

  13. [13]

      Tse, S. C.; Tsung, K. K.; So, S. K. Appl. Phys. Lett. 2007, 90, 213502. doi: 10.1063/1.2740110

  14. [14]

      Kasparek, C.; Rorich, I.; Blom, P. W. M.; Wetzelaer, G. J. A. H. J. Appl. Phys. 2018, 123, 024504. doi: 10.1063/1.5007329

  15. [15]

      Kim, J. H.; Chen, Y.; Liu, R.; So, F. Org. Electron. 2014, 15, 2381. doi: 10.1016/j.orgel.2014.07.012

  16. [16]

      Choi, W. H.; Cheung, C. H.; So, S. K. Org. Electron. 2010, 11, 872. doi: 10.1016/j.orgel.2010.02.001

  17. [17]

      Zheng, H.; Zhang, F.; Zhou, N. L.; Su, M. N.; Li, X. G.; Xiao, Y.; Wang, S. R. Org. Electron. 2018, 56, 89. doi: 10.1016/j.orgel.2018.01.038

  18. [18]

      Zhu, W. J.; Chen, X. L.; Chang, J. F.; Yu, R. M.; Li, H. R.; Liang, D.; Wu, X. Y.; Wang, Y. S.; Lu, C. Z. J. Mater. Chem. C 2018, 6, 7242. doi: 10.1039/c8tc01005f

  19. [19]

      Tsai, C. T.; Liu, Y. H.; Tang, J. F.; Kao, P. C.; Chiang, C. H.; Chu, S. Y. Synth. Met. 2018, 243, 121. doi: 10.1016/j.synthmet.2018.06.008

  20. [20]

      Zhang, X. W.; Zheng, Q. H.; Tang, Z. Y.; Li, W. S.; Zhang, Y.; Xu, K.; Xue, X. G.; Xu, J. W.; Wang, H.; Wei, B. Appl. Phys. Lett. 2018, 112, 083302. doi: 10.1063/1.5016411

  21. [21]

      Xu, H. T.; Zhou, X. J. Appl. Phys. 2013, 114, 244505. doi: 10.1063/1.4852835

  22. [22]

      You, H.; Dai, Y. F.; Zhang, Z. Q.; Ma, D. G. J. Appl. Phys. 2007, 101, 026105. doi: 10.1063/1.2430511

  23. [23]

      Chiu, T. L.; Chuang, Y. T. J. Nanosci. Nanotech. 2015, 15, 9207. doi: 10.1166/jnn.2015.11415

  24. [24]

      Lv, Z. Y.; Deng, Z. B.; Xu, D. H.; Li, X. F.; Jia, Y. Displays 2009, 30, 23. doi: 10.1016/j.displa.2008.10.001

  25. [25]

      牛连斌, 关云霞.物理学报, 2009, 58, 4931. doi: 10.7498/aps.58.4931Niu, L. B.; Guan, Y. X. Acta Phys. Sin. 2009, 58, 4931. doi: 10.7498/aps.58.4931

  26. [26]

      Lee, J. Y.; Kwon, J. H. Appl. Phys. Lett. 2005, 86, 063514. doi: 10.1063/1.1861962

  27. [27]

      Yuan, Y.; Grozea, D.; Lu, Z. H. Appl. Phys. Lett. 2005, 86, 143509. doi: 10.1063/1.1899241

  28. [28]

      Li, X. C.; Xie, F. X.; Zhang, S. Q.; Hou, J. H.; Choy, W. C. H. Adv. Funct. Mater. 2014, 24, 7348. doi: 10.1002/adfm.201401969

  29. [29]

      Yang, J. P.; Wang, W. Q.; Cheng, L. W.; Li, Y. Q.; Tang, J. X.; Kera, S.; Ueno, N.; Zeng, X. H. J. Phys.:Condens. Matter 2016, 28, 185502. doi: 10.1088/0953-8984/28/18/185502

  30. [30]

      Zhang, H. M.; Fu, Q.; Zeng, W. J.; Ma, D. G. J. Mater. Chem. C 2014, 2, 9620. doi: 10.1039/c4tc01310g

  31. [31]

      Pandey, R.; Gunawan, A. A.; Mkhoyan, K. A.; Holmes, R. J. Adv. Funct. Mater. 2012, 22, 617. doi: 10.1002/adfm.201101948

  32. [32]

      Lee, H.; Kim, J. Y.; Lee, C. Int. J. Photoenergy 2012, 2012, 581421 doi: 10.1155/2012/581421

  33. [33]

      Shin, W. J.; Lee, J. Y.; Kim, J. C.; Yoon, T. H.; Kim, T. S.; Song, O. K. Org. Electron. 2008, 9, 333. doi: 10.1016/j.orgel.2007.12.001

•