Electroluminescence efficiency and stability of near ultraviolet organic light-emitting diodes based on BCPO luminous materials

Ren Xing; Yu Hong-Yu; Zhang Yong

doi:10.7498/aps.73.20231301

Abstract

To date, in the traditional method of obtaining near-ultraviolet (NUV) light, mercury atoms, which can create a highly toxic heavy metal contaminant, have been used. Therefore, it is an important issue to obtain NUV light by using new environmentally friendly devices. In the last decade, the fabrication of near ultraviolet organic light-emitting diodes (NUV-OLEDs) has become a research hotspot in the field of organic electronics. However, when the electroluminescence wavelength is extended to shorter than 400 nm, higher requirements are put forward for the materials used for each functional layer in these devices. In this work, a wide bandgap small molecule material of BCPO is used as the luminescent layer. The electron-transporting and hole-transporting materials are determined based on the overlaps between absorption spectra of these materials and emission spectrum of BCPO. And NUV-OLEDs with electroluminescent peak wavelength at 384 nm are prepared. By using the optimal device structure, the maximum external quantum efficiency of the device reaches 2.98%, and the maximum radiance of the device reaches 38.2 mW/cm². In the electroluminescence spectrum, NUV light with wavelengths below 400 nm accounts for 57% of the light emission. In addition, the device demonstrates good stability when biased at two different constant voltage modes. The multiple key factors which affect the stability of the device are analyzed in detail. Firstly, it is found that the high glass transition temperature (T_g) of hole-transporting material is very important for the long-time stability of this device. The poor device stability is closely related to the low T_g temperature of hole-transporting material. Secondly, due to the widespread use of PEDOT:PSS as hole injection material in OLEDs, the electron leakage from the hole-transpor layer into the PEDOT:PSS layer may cause significant damage to the conducting polymer. When bombarded with low energy electrons, bond breakage occurs on the surface of PEDOT:PSS, followed by the release of oxygen and sulfur, resulting in changes in conductivity and oxidation reactions with molecules of hole transport material. Thirdly, the photoelectrical stability of organic molecules is the most fundamental reason that restricts the device lifetime. The aging process of material or device is directly relevant to the bond dissociation energy (BDE) of organic molecule. Generally, the BDE value of organic molecule is not high enough. As a result, molecules are prone to chemical bond breakage during electrochemical or photochemical aging. In summary, highly stable NUV-OLEDs should be fabricated by using hole-transporting materials with high T_g temperature, sufficient electron-blocking capacity, and large BDE value.

Keywords:

Authors and contacts

Chongqing Key Laboratory of Micro & Nano Structure Optoelectronics, School of Physical Science and Technology, Southwest University, Chongqing 400715, China

Corresponding author: Zhang Yong, yzh6127@swu.edu.cn

[1]	连加荣, 曾鹏举 2010 现代显示 118 35 Google Scholar Lian J R, Zeng P J 2010 Adv. Disp. 118 35 Google Scholar
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[26]	So F, Kondakov D 2010 Adv. Mater. 22 3762 Google Scholar
[27]	Song W, Lee J Y 2017 Adv. Optical Mater. 5 1600901 Google Scholar
[28]	Lee H L, Lee K H, Lee J Y 2019 Dyes and Pigments 171 107714 Google Scholar
[29]	Dong S C, Xu L S, Tang C W 2017 Org. Electron. 42 379 Google Scholar
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Cited By

图 1 BCPO薄膜的发射光谱与TPBi, TpPyPB, TmPyPB薄膜的吸收光谱对比

Figure 1. Comparison between emission spectrum of BCPO film and absorption spectra of TPBi, TpPyPB and TmPyPB films.

DownLoad: Full-Size Img PowerPoint

图 2 BCPO薄膜的发射光谱与NPB, TCTA, TAPC薄膜的吸收光谱对比

Figure 2. Comparison between emission spectrum of BCPO film and absorption spectra of NPB, TCTA and TAPC films.

DownLoad: Full-Size Img PowerPoint

图 3 ITO阳极与PEDOT:PSS薄膜的透射率

Figure 3. Transmission of ITO anode and PEDOT:PSS films.

DownLoad: Full-Size Img PowerPoint

图 4 具有不同空穴传输层器件的性能对比　(a) J-V曲线; (b) R-V曲线; (c) EQE-J曲线; (d)器件结构图

Figure 4. Performance comparison of devices with different hole-transporting layers: (a) J-V curves; (b) R-V curves; (c) EQE-J curves; (d) diagram of device structure.

DownLoad: Full-Size Img PowerPoint

图 5 DEV1, DEV2, DEV3在两种恒压模式下的稳定性对比　(a) R₀ = 2 mW/cm²; (b) R₀ = 10 mW/cm²

Figure 5. Comparison of stabilities of DEV1, DEV2 and DEV3 under two constant voltage modes: (a) R₀ = 2 mW/cm²; (b) R₀ = 10 mW/cm².

DownLoad: Full-Size Img PowerPoint

图 6 TAPC与TCTA的分子结构与化学键解离能

Figure 6. Molecular structures and bond dissociation energies of TAPC and TCTA molecules.

DownLoad: Full-Size Img PowerPoint

表 1 三种电子传输材料的性能参数对比

Table 1. Comparison of property parameters of three electron-transporting materials.

材料名称 E_HOMO/E_LUMO/eV E_g/eV μ_e/(10^–3 cm²·V^–1·s^–1) T_g/℃

TPBi –6.2/–2.7 3.5 0.1 76

TpPyPB –6.65/–3.04 3.61 3.4—7.9 79

TmPyPB –6.7/–2.7 4.0 1.0 79

DownLoad: CSV

表 2 三种空穴传输材料的性能参数对比

Table 2. Comparison of property parameters of three hole-transporting materials.

材料名称 E_HOMO/E_LUMO/eV E_g/eV μ_h/(10^–3 cm²·V^–1·s^–1) T_g/℃

NPB –5.5/–2.0 3.5 1.0 95

TCTA –5.7/–2.3 3.4 0.19 151

TAPC –5.5/–2.0 3.5 10 78

DownLoad: CSV

表 3 具有不同空穴传输层器件的性能对比

Table 3. Performance comparison of devices with different hole-transporting layers.

器件名称 V_on/V R_max/(mW·cm^–2) EQE_max/%

DEV1 3.5 38.7 2.69

DEV2 4.0 22.6 2.08

DEV3 3.5 38.2 2.98

DownLoad: CSV

[1]	连加荣, 曾鹏举 2010 现代显示 118 35 Google Scholar Lian J R, Zeng P J 2010 Adv. Disp. 118 35 Google Scholar
[2]	Chen M Y, Liao Y J, Lin Y, Xu T, Lan W X, Wei B, Yuan Y F, Li D L, Zhang X W 2020 J. Mater. Chem. C 8 14665 Google Scholar
[3]	娄敬丽, 黎刚刚, 王志明, 唐本忠 2023 发光学报 44 37 Google Scholar Lou J L, Li G G, Wang Z M, Tang B Z 2023 Chin. J. Lumin. 44 37 Google Scholar
[4]	王瀚洋, 朱元烨, 谢凤鸣, 李艳青, 唐建新 2023 发光学报 44 140 Google Scholar Wang H Y, Zhu Y Y, Xie F M, Li Y Q, Tang J X 2023 Chin. J. Lumin. 44 140 Google Scholar
[5]	杨文静, 孙玥, 叶丹, 王姣, 张伟, 李晓蕾, 王先良 2017 环境与健康 34 1100 Google Scholar Yang W J, Sun Y, Ye D, Wang J, Zhang W, Li X L, Wang X L 2017 J. Environ. Health 34 1100 Google Scholar
[6]	Li Z G, Jia P Q, Zhao F, Kang Y K 2018 Int. J. Environ. Res. Public Health 15 2766 Google Scholar
[7]	Mikami A, Mizuno Y, Takeda S 2008 SID Symp. Dig. Tech. Pap. 39 215 Google Scholar
[8]	Zhang X W, You F J, Liu S Q, Mo B J, Zhang Z L, Xiong J, Cai P, Xue X G, Zhang J, Wei B 2017 Appl. Phys. Lett. 110 043301 Google Scholar
[9]	Lin J, Guo X Y, Lü Y, Liu X Y, Wang Y 2020 ACS Appl. Mater. Interfaces 12 10717 Google Scholar
[10]	Luo Y J, Li S B, Zhao Y H, Li C, Pang Z G, Huang Y, Yang M H, Zhou L, Zheng X J, Pu X M, Lu Z Y 2020 Adv. Mater. 32 2001248 Google Scholar
[11]	Zhang H, Li G G, Guo X M, Zhang K, Zhang B, Guo X C, Li Y X, Fan J Z, Wang Z M, Ma D G, Tang B Z 2021 Angew. Chem. 133 22415 Google Scholar
[12]	Li G G, Li B X, Zhang H, Guo X C, Lin C W, Chen K Q, Wang Z M, Ma D G, Tang B Z 2022 ACS Appl. Mater. Interfaces 14 10627 Google Scholar
[13]	Chen J K, Liu H, Guo J J, Wang J H, Qiu N L, Xiao S, Chi J J, Yang D Z, Ma D G, Zhao Z J, Tang B Z 2022 Angew. Chem. 61 e202116810 Google Scholar
[14]	Peng L, Lü J C, Xiao S, Huo Y M, Liu Y C, Ma D G, Ying S A, Yan S K 2022 Chem. Eng. J. 450 138339 Google Scholar
[15]	马治军, 雷霆, 裴坚, 刘晨江 2013 化学进展 25 961 Google Scholar Ma Z J, Lei T, Pei J, Liu C J 2013 Prog. Chem. 25 961 Google Scholar
[16]	王芳芳, 陶友田, 黄维 2015 化学学报 73 9 Google Scholar Wang F F, Tao Y T, Huang W 2015 Acta Chim. Sinica 73 9 Google Scholar
[17]	Chou H H, Cheng C H 2010 Adv. Mater. 22 2468 Google Scholar
[18]	Yan F, Xing G C, Chen R, Demir H V, Sun H D, Sum T C, Sun X W 2015 Appl. Phys. Lett. 106 023302 Google Scholar
[19]	Knauer K A, Najafabadi E, Haske W, Kippelen B 2012 Appl. Phys. Lett. 101 103304 Google Scholar
[20]	Wang S M, Wang X D, Yao B, Zhang B H, Ding J Q, Xie Z Y, Wang L X 2015 Sci. Rep. 5 12487 Google Scholar
[21]	Chu T Y, Song O K 2007 Appl. Phys. Lett. 90 203512 Google Scholar
[22]	Gao C H, Zhou D Y, Gu W, Shi X B, Wang Z K, Liao L S 2013 Org. Electron. 14 1177 Google Scholar
[23]	Kim J H, Chen Y, Liu R, So F 2014 Org. Electron. 15 2381 Google Scholar
[24]	牛泉, 郝洪敏, 林雯欣, 黄江夏 2023 发光学报 44 186 Google Scholar Niu Q, Hao H M, Lin W X, Huang J X 2023 Chin. J. Lumin. 44 186 Google Scholar
[25]	Van Der Gon A W D, Birgerson J, Fahlman M, Salaneck W R 2002 Org. Electron. 3 111 Google Scholar
[26]	So F, Kondakov D 2010 Adv. Mater. 22 3762 Google Scholar
[27]	Song W, Lee J Y 2017 Adv. Optical Mater. 5 1600901 Google Scholar
[28]	Lee H L, Lee K H, Lee J Y 2019 Dyes and Pigments 171 107714 Google Scholar
[29]	Dong S C, Xu L S, Tang C W 2017 Org. Electron. 42 379 Google Scholar
[30]	Kondakov D 2008 J. Appl. Phys. 104 084520 Google Scholar

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