Effects of the Thickness of the Hole Transport Layer on the Performance of Graphene-based Organic Light-emitting Diodes

doi:10.11901/1005.3093.2023.198

Chinese Journal of Materials Research

2024, Vol. 38

Issue (3): 168-176 DOI: 10.11901/1005.3093.2023.198

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Effects of the Thickness of the Hole Transport Layer on the Performance of Graphene-based Organic Light-emitting Diodes

LIU Rui¹^,², ZHANG Dingdong², ZHANG Hui¹(

), REN Wencai², DU Jinhong²(

)

^1.School of Materials Science and Engineering, Shenyang University of Chemical Technology, Shenyang 110142, China
^2.Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Cite this article:

LIU Rui, ZHANG Dingdong, ZHANG Hui, REN Wencai, DU Jinhong. Effects of the Thickness of the Hole Transport Layer on the Performance of Graphene-based Organic Light-emitting Diodes. Chinese Journal of Materials Research, 2024, 38(3): 168-176.

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Abstract

Thickness modulation is an important way to improve the performance of organic light-emitting diode (OLED) device. In this paper, flexible green OLED devices were constructed by vacuum thermal evaporation, using graphene as the transparent anode and 1,1-bis[4-[N,N-bis(p-tolyl)amino]phenyl]cyclohexane (TAPC) as the hole transport layer. The effects of evaporation speed on the morphology of the TAPC layer and the thickness of TAPC layer on the device performance were studied. First, 60 nm-thick TAPC layers were fabricated by controlling the evaporation speed at 0.05, 0.1 and 0.15 nm·s^-1. It was found that the TAPC film had the lowest surface roughness of ~2.52 nm when the evaporation speed was 0.05 nm·s^-1. Subsequently, TAPC layers with thicknesses of 50, 60, 70 and 80 nm were fabricated at a evaporation speed of 0.05 nm·s^-1 and OLED devices were fabricated while keeping the thickness of other functional layers unchanged. A comparative study showed that the device with 70 nm-thick TAPC layer achieved the highest performance with a maximum brightness of 34350 cd·m^-2 and a maximum external quantum efficiency (EQE) of 21.02%. Meanwhile, the device has excellent flexibility and the CIE chromaticity coordinate is located at (0.3140, 0.6386), which is very close to the chromaticity coordinate of standard green light. This study is significant for promoting the application of flexible graphene-based OLEDs in the fields of display and lighting and for the development of wearable optoelectronic devices.

Key words: inorganic non-metallic materials organic light-emitting diodes hole transport layers graphene flexible optoelectronics

Received: 23 March 2023

ZTFLH:

TN383.1

Fund: National Science Foundation of China(52002375);National Science Foundation of China(52272051);China Postdoctoral Science Fo-undation(2020M670812);China Postdoctoral Science Fo-undation(2020TQ0328);Liaoning Province Science and Technology Planning Project(2021-BS-003)

Corresponding Authors: ZHANG Hui, Tel:13998243835, E-mail: krista9150@sina.com;DU Jinhong, Tel:(024)83970720, E-mail: jhdu@imr.ac.cn

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	LIU Rui
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https://www.cjmr.org/EN/10.11901/1005.3093.2023.198 OR https://www.cjmr.org/EN/Y2024/V38/I3/168

Fig.1 Organic materials used in OLED devices (a) Molecular structure of TAPC, (b) Ir(ppy)₂acac, (c) Bepp₂ and (d) BPhen

Fig.2 Device structure (a) and Energy level diagram (b) of the G-OLED

Fig.3 Morphologies of PET/3L-G/MoO₃ (a) and TAPC layer on PET/3L-G/MoO₃ fabricated at evaporation rate of 0.05 nm·s^-1(b), 0.1 nm·s^-1 (c) and 0.15 nm·s^-1 (d)

Fig.4 Device performance of OLED with different thickness of TAPC layers (a) current density-voltage (J-V) curve; (b) luminance-voltage (L-V) curve; (c) current efficiency-luminance (CE-L) curve; (d) power efficiency-luminance (PE-L) curve; (e) external quantum efficiency-luminance (EQE-L) curve; (f) electroluminescence spectra; (g) current effici-ency maximum; (h) power efficiency maximum; (i) external quantum efficiency maximum

Table 1 Performance parameters of G-OLED devices

Fig.5 Morphology of OLED devices with different thickness of TAPC (a) 50 nm; (b) 60 nm; (c) 70 nm; (d) 80 nm. (e) the structure of hole-only device; (f) current density-voltage characteristics of hole-only devices

Fig.6 Performance of flexible green G-OLED devices (a) CIE chromatogram of OLED device; (b) surface resistance change of graphene film after a thousand bending; (c) brightness change of OLED device after a thousand bending; (d) photograph and emission performance of flexible green OLED devices fabricated by using 70 nm-thick TAPC as HTL, lighting area of 2 mm × 2 mm; (e) photograph of lighting OLED device under bending

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