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It is difficult to enhance the blue or purple luminescence efficiency of organic light-emitting device ( OLED) for practice display applications. In this work, aluminum nano particles (Al-NPs) are inserted into the light-tight TmPyPb electron transporting layer (ETL) of ITO/PEDOT:PSS/TAPC/BCzVBi:BCPO/TmPyPb/Liq/Al OLEDs, in which BCzVBi can emit deep-blue fluorescent light, with the attempts to overcome the above deficiency through the local surface plasmon polariton (LSPP) effect excited in Al-NP at higher resonance frequencies by the luminescence radiations from BCzVBi. The distances of Al-NPs from BCzVBi:BCPO fluorescent layer are chosen as x = 4, 8, 12 nm. The morphologies observed by atom force microscope and scan electron microscope show that the Al film with a thickness of 1 nm, deposited at room temperature by vacuum heat evaporate, is composed of separated Al grains (therefore, called Al-NPs) with sizes on a 10 nm scale. By inserting these Al-NPs into the TmPyPb ETL, both the current density and luminance at the same voltage decrease in comparison with the counterparts of reference devices (i.e. ones without Al-NPs) due to the worsened carrier mobility. However, the current density and luminance both rebound significantly at x = 8 nm. This may be due to the fact that the fluorescence quenching strongly occurs at x < 8 nm, and on the other hand, the local surface plasmon polariton is weakened too much at x > 8 nm due to attenuated radiation from BCzVBi. At x = 8 nm, the voltage (9 V) at which the luminance reaches a maximum value is the same as that for the reference device, but the maximum luminance itself decreases from 4200 Cd/m2 to 3500 Cd/m2. However, the current density also decreases from 335.19 mA/cm2 to 145.71 mA/cm2. This conversely results in a promising great increase of current efficiency from 0.88 Cd·A–1 to 2.36 Cd·A–1. Subsequently, the external quantum efficiency (EQE) is enhanced by 170%, while the efficiency roll-off ratio decreases from 78% to 30.5%, with a decrement of 61%. At a high current density of 270 mA/cm2, EQE enhances 66.5%. The coupling between fluorescence excitation state and local surface plasmon polariton is determined by the overlapping between fluorescence emitting peak and plasmon resonance peak. As aluminum has a number density of free electrons, 18.1×1022 cm–3, much larger than those for the other normally used metals (such as gold and silver), its spectrum of local surface plasmon polariton is enough to cover the fluorescence wavelength range of BCzVBi. These research results show that the luminescence efficiency of deep-blue OLEDs can be turned better by LSPP excited in Al-NPs at higher resonance frequencies.
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Keywords:
- deep-blue organic light emitting device /
- localized surface plasmon polariton /
- Al nanometer particle /
- luminescence efficiency.
[1] 彭灵 2019 博士学位论文 (广州: 华南理工大学)
Peng L 2019 Ph. D. Dissertation (Guangzhou: South China University of Technology
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图 2 器件结构能级图
Figure 2. Energy level diagram of reference device.
图 1 (a) TmPyPb层内嵌入Al-NPs的器件结构(x = 4, 8, 12 nm); (b) 对比器件结构
Figure 1. (a) Structures of devices with Al-NPs inserted in TmPyPb layer (x = 4, 8, 12 nm); (b) structures of reference device.
图 3 (a) TmPyPb, 以及在TmPyPb上生长 (b) 0.7, (c) 1.0, (d) 1.3 nm厚Al膜的表面形貌; 主图为AFM图像, 下方附图为SEM图像
Figure 3. AFM (with inserted SEM if necessary) images of (a) TmPyPb; (b) 0.7, (c) 1.0, (d) 1.3 nm thick Al films grown on TmPyPb.
图 4 (a) BCzVBi:BCPO的稳态光致发射谱; (b) 瞬态荧光衰减曲线
Figure 4. (a) PL emission spectra of BCzVBi:BCPO; (b) fluorescence attenuation curves.
图 5 有无Al-NPs修饰OLED的电压-电流密度-亮度-电流效率-外量子效率特性图
Figure 5. Voltage-current density-luminance-current efficiency-EQE characteristic curves of OLEDs modified with and without Al-NPs.
图 6 有无Al-NPs修饰OLED的效率滚降比
Figure 6. Roll-off ratios of OLEDs modified with and without Al-NPs.
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[1] 彭灵 2019 博士学位论文 (广州: 华南理工大学)
Peng L 2019 Ph. D. Dissertation (Guangzhou: South China University of Technology
[2] Jou J H, Kumar S, Agrawal A, Li T H, Sahoo S 2015 Mater. Chem. C 3 3500
Google Scholar
[3] Wang S, Lei Z, Zhang B, Ding J, Xie Z, Wang L, Wong W Y 2018 iScience 6 128
Google Scholar
[4] Miao Y, Wang K, Zhao B, Gao L, Tao P, Liu X, Hao Y, Wang H, Xu B, Zhu F 2018 Nanophotonics 7 295
Google Scholar
[5] Wang S L, Yang J L, Tao X, Dou D H, Tang Z Y, Gao Z X, Chen M Y, Guo K P, Yu J S, Plain J, Bachelot R, Zhang J H, Wei B 2019 Org. Electron. 64 146
Google Scholar
[6] Wang S, Qiao M, Ye Z, Dou D, Chen M Y, Peng Y, Shi Y, Yang X Y, Cui L, Li J Y 2018 iScience 9 532
Google Scholar
[7] Yang L S, Meng H F, Chang Y F, Lien Y F, Zan H W, Hong S F, Duan L, Qiu Y 2017 Org. Electron. 51 6
Google Scholar
[8] Chen S F, Deng L L, Xie J, Peng L, Xie L H, Fan Q L, Huang W 2010 Adv. Mater. 22 5227
Google Scholar
[9] Xu T, Li W, Wu X, Ahmadi M, Xu L, Chen P 2020 Mater. Chem. C 8 6615
Google Scholar
[10] Hu J B, Yu Y, Jiao B, Ning S Y, Dong H, Hou X, Zhang Z J, Wu Z X 2016 Org. Electron. 31 234
Google Scholar
[11] 虞华康, 刘伯东, 吴婉玲, 李志远 2019 物理学报 68 149101
Google Scholar
Yu H K, Liu B D, Wu W L, Li Z Y 2019 Acta Phys. Sin. 68 149101
Google Scholar
[12] Deng L L, Zhou Z J, Jia B L, Zhou H W, Ling P, Shang W J, Jing F, Chen S F 2018 Org. Electron. 53 346
Google Scholar
[13] Fusella M A, Saramak R, Bushati R, Menon V M, Weaver M S, Thompson N J, Brown J J 2017 Nature 585 379
Google Scholar
[14] 吴小龑, 熊自阳, 吴凌远, 李阳龙, 付博, 刘国栋, 王伟平, 陈平 2017 光学学报 37 274
Google Scholar
Wu X Y, Xiong Z Y, Wu L Y, Li Y L, Fu B, Liu G D, Wang W P, Chen P 2017 Acta Opt. 37 274
Google Scholar
[15] Zhong Z, Lian H, Wu J, Cheng X Z, Wang H, Dong Q C, Zhu F R 2018 Org. Electron. 56 31
Google Scholar
[16] Yu Y, Ma L, Wang D D, Zhou H X, Yao B, Wu Z X 2017 Org. Electron. 19 173
Google Scholar
[17] Raether H 1988 Springer Tracts in Modern Physics (Berlin: Verlag) p111
[18] Novotny L, Hecht B 2012 Principles of nano-optics (2nd Ed.) (Cambridge: Cambridge University) pp399−417
[19] Gérard D, Gray K S 2015 Physics D 48 184001
Google Scholar
[20] 马守宝, 刘琼, 钱晓晨, 洪瑞金, 陶春先 2017 光学学报 37 364
Google Scholar
Ma S B, Liu Q, Qian X C, Hong R J, Tao C X 2017 Acta Opt. 37 364
Google Scholar
[21] Lu G W, Liu J, Zhang T Y, Shen H M, Perriat P, Martini M, Tillement O, Gu Y, He Y B, Wang Y W, Gong Q H 2013 Nanoscale 5 6545
Google Scholar
[22] Chou R Y, Lu G, Shen H, He Y, Cheng Y, Perriat P, Martini M, Tillement O, Gong Q 2014 Appl. Phys. 115 224
Google Scholar
[23] Peng J, Xu X, Yuan T, Wang J, Li L 2014 Appl. Phys. 105 173
Google Scholar
[24] Liu J, Li Y, Wang S, Ling Z, Wei B 2019 J. Alloys Compd. 814 152299
Google Scholar
[25] Fujiki A, Uemura T, Zettsu N, Akai-Kasaya M, Saito A, Kuwahara Y 2010 Appl. Phys. Lett. 96 14
Google Scholar
[26] Zhang D D, Wang R, Ma Y Y, Wei H X, Ou Q D, Wang Q K, Zhou L, Lee S T, Li Y Q, Tang J X 2014 Org. Electron. 15 961
Google Scholar
[27] Ji W Y, Zhao H F, Yang H G, Zhu F R 2015 Org. Electron. 22 154
Google Scholar
[28] Lee M H, Choi W H, Zhu F R 2016 Org. Express 24 A596
Google Scholar
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