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Interface Anchored Effect on Improving Working Stability of Deep Ultraviolet Light-Emitting Diode Using Graphene Oxide-based Fluoropolymer Encapsulant Renli Liang, Jiangnan Dai, Linlin Xu, Yi Zhang, Ju He, Shuai Wang, Jingwen Chen, Yang Peng, Lei Ye, Hao-Chung Kuo, and Changqing Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b17668 • Publication Date (Web): 01 Feb 2018 Downloaded from http://pubs.acs.org on February 2, 2018
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ACS Applied Materials & Interfaces
Interface Anchored Effect on Improving Working Stability of Deep Ultraviolet Light-Emitting Diode Using
Graphene
Oxide-based
Fluoropolymer
Encapsulant Renli Liang1 ,Jiangnan Dai1*, Linlin Xu1, Yi Zhang1, Ju He1, Shuai Wang1, Jingwen Chen1, Yang peng2, Lei Ye3*, Hao-chung Kuo4* and Changqing Chen1
1 Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan, 430074, China
2 School of Mechanical Science & Engineering, Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan, 430074, China
3 School of Optical and Electronic Information， Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan, 430074, China
4 Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 300, Taiwan Corresponding email address:
[email protected];
[email protected];
[email protected] 1 ACS Paragon Plus Environment
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KEYWORDS: interface anchored effect, graphene oxide-based fluoropolymer encapsulant, deep ultraviolet light-emitting diode, light extraction efficiency, working stability
ABSTRACT The graphene oxide (GO)-based fluoropolymer is firstly proposed as interface encapsulant to improve the light extraction efficiency (LEE) and achieve the ultra-long working stability of
deep ultraviolet light-emitting diode (DUV-LEDs) benifit from its
superior interface performance based on anchored effect. For the GO-based fluoropolymer composite, the anchored structure is designed to effectively tightly rivet the quartz lens on the DUV-LED chip by using the interface reaction between GO embedded in fluoropolymer and 3-aminopropyltriethoxy-silane (APTS) grafted on the surfaces. Experimental results show that based on the interface anchored effect, the air voids in interface layer of DUV-LED is reduced by 84%, leading to an improvement of light output power by 15% and a decrease of junction temperature by 5%, by virtue of the sealing characteristics of the 0.10 wt% GObased fluoropolymer. In addition, the steadily working time is dramatically improved by 660%, and it was attributed to the good interface anchored bonding of the 0.10 wt% GObased fluoropolymer. This novel graphene oxide-based fluoropolymer is believed to provide a feasible and effective interface encapsulant to improve the performance of DUV-LEDs.
1. Introduction AlGaN-based deep-ultraviolet LEDs (DUV-LEDs) (λ < 300 nm) have greatly attracted many scientists’ attention due to their wide range of applications, such as in radiation curing, sterilization, water purification, counterfeit detection, and sensor applications in place of traditional UV lamps1-6. However, the poor light extraction efficiency (LEE) and aging of packaging materials limit the development of DUV2 ACS Paragon Plus Environment
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ACS Applied Materials & Interfaces
LEDs7,
leading to the bad optical performance8-12 and working stability13-16. To
circumvent the two issues, many researches about DUV-LEDs are usually working on researching encapsulant materials. The encapsulant sandwiched between chip and quartz lens plays a major role in improving the performance of DUV-LEDs, such as light extraction, transferring heat, extending product life and environmental protection17-21. But the conventional encapsulants for LED lighting devices, which usually include the solution-processable thermosetting epoxy or organo-siloxane resins, are easily destroyed by UV-light from DUV-LEDs because of the existence of the UV-sensitive organic groups in the conventional encapsulants, and it will lead to the light failure and short-term working stability of DUV-LEDs22-23. Hence, a novel GO-based fluoropolymer composite was firstly fabricated via a solventexchange method as the interface encapsulant to improve the performance of DUV-LEDs. The fluoropolymer with a stable –CF3 end (S-tpye, CYTOP) has been proved its excellent transparency and good stability under deep ultraviolet
14, 16, 24-25
but comparatively poor
bonding ability 26-28. It may cause unexpected air voids in their interfaces, and induce the bad influence both on the light spread and heat transfer in the encapsulation29-32, especially the substantial erosion of the moisture-oxygen at a high risk of device failure33-35. Therefore, owing to ultrahigh thermal conductivity 36, high Young’s modulus 37 fracture strength 38, and many functional groups
39-40
, graphene oxide is proverbially used as the packaging
composite materials to improve the thermal, optical and reliable characteristics of semiconductor devices, for example, as highly efficient thermal interface materials41-43, bonding paste44 and encapsulant filler45. By using GO with as a filler, the GO-based fluoropolymer can possess the similar “anchored crosslinks” to reveal its better bonding ability than that of the neat fluoropolymer. It is attributed to the “anchored effect” which can be described that the GO as the anchor embedded in the fluoropolymer will react to link the APTS as the cable grafted both on the surface of quartz lens and DUV-LED chip, making 3 ACS Paragon Plus Environment
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tightly fixation between the quartz lens and the chip. Furthermore, the GO-based fluoropolymer composite also possesses some good characteristics such as superior consistency and barrier capacity benefit from multifunctional GO
45-46
as a filler. Compared
with the traditional fluoropolymer encapsulant, the DUV-LEDs with the proposed interface encapsulant shows better light extraction efficiency, lower junction temperature and superior long-term working stability. This novel GO-based fluoropolymer composite as the interface encapsulant is believed to provide a simple and effective strategy for improving the performance of DUV-LEDs.
2. Fabrication, Results and Discussion The fabrication process of the DUV-LEDs with GO-based fluoropolymer is schematically illustrated in Figure 1. The fluid B (Figure 1b) contained 1 wt% APTS was adopted to modify the surface of DUV-LED chip and quartz lens, and the stable GO-based fluoropolymer can be formed using a solvent-exchange method as Figure 1d and Figure 1e displayed, which is an effective and simple approach to obtain uniformly dispersed nanocomposite. The fluoropolymer with different GO contents of 0.02 wt %, 0.04 wt%, 0.06 wt%, 0.08 wt%, 0.10 wt% and 0.20 wt% was fabricated, respectively. Meanwhile, experimental results indicated that the transmittance of GObased fluoropolymer composites is relatively high for UV-light, suggesting that the GO-based fluoropolymer composites (GO content
