Highly flexible and stretchable transparent electrodes fabrication by length and diameter controlled silver nanowires길이와 두께가 제어된 은 나노와이어를 이용한 매우 유연하고 신축 가능한 투명전극 생성에 관한 연구

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Nanostructures including quantum dot, nanoparticles, carbon-nanotube (CNT), graphene, and nanowires have been extensively studied and explored for applications such as optical devices, electrical device, and biosensors due to their promising characteristics. One dimensional noble metal nanowires are vigorously applied through their unique properties which cannot be found in bulk state. For instance, Silver nanowires have been extensively studied since they play important roles in practical devices. Among the various strategies for Ag nanowire synthesis, polyol process is regarded as an ideal method due to such advantages as rapidity, high yield ratio and repeatability. In spite of these advantages, controlling the length is difficult and the aspect ratio of a silver nanowire is usually limited to 100 ~ 400. In this study, we developed a novel approach to synthesize longer and higher aspect ratio Ag nanowires with higher yield. First, we performed extensive parametric studies to find the optimum condition for ultra-long Ag nanowire synthesis by controlling external conditions, such as different types and combinations of stir bar, RPM, sonication effect and injection speed. Second, a novel synthesis approach called a successive multi-step growth (SMG) is introduced to increase the aspect ratio of silver nanowire even further. It has been confirmed that the silver nanowire, after its initial growth, can continue to grow as long as the Ag-ion rich condition is repeatedly provided. Through the scheme of a SMG method, we successfully obtained extremely high aspect ratio (1000 to 3000) silver nanowires of $300 \mu m$ in length with 150 nm diameter. Moreover, highly bendable Ag Nanowires film with low sheet resistance and high transmittance are demonstrated on various substrates through vacuum filtration and rod deposition method. These results suggested that this is an important step toward producing intelligent and multifunctional soft electric devices for human friendly electronics interface, and it may ultimately contribute to the applications in wearable computers. Although there are various methods to fabricate transparent electrodes with silver nanowires, high temperature post-process have been required to remove polymer layer on silver nanowire surfaces. However, thermal annealing is not applicable for flexible substrates such as PET and PEN because it can be bent of melt by heat source. In this study, room temperature process has been developed for silver nanowires network transparent electrodes on flexible substrates. First, selective laser welding process have been developed using 532 nm laser. The laser is a monochromatic photon source which maximizes the photon energy coupling into the nanowire junction with much higher e-field enhancement. The low temperature process nature of the laser nano-welding can allow the use of flexible substrates which are usually heat sensitive and easily damaged or hardened to lose flexibility during the high thermal annealing process. Therefore, flexible transparent electrode have been successfully fabricated without thermal annealing. Second, We demonstrated that using a AgNW/ PEDOT:PSS hybrid composite, contact resistance and substrate adhesion problem could be significantly enhanced even without a high temperature annealing step. Through the strong adhesion enhancement and the flexible nature of the AgNW and conducting polymer, a flexible transparent electrode on a flexible polymer substrate could be demonstrated. Furthermore, I demonstrated a highly stretchable metal conductor of Very long Ag Nanowire Percolation Network (VAgNPN) on a pre-strained, highly stretchable elastomer, which can be stretched up to 900% without failure. Fabricated highly stretchable VAgNPN conductor could be stretched to over 460% strain without a notable resistance increase. There have been several reports of the individual strengths and advantages of other stretchable conductors, but no materials including CNTs, graphene, metal thin films, and metal NWs have achieved this level of stretchability and durability, as well as low resistance. Moreover, I suggested and demonstrated hierarchical multiscale AgNW/CNT hybrid nanocomposite, which takes advantage of enhanced mechanical compliance and optical transparency of CNTs as well as enhanced electrical conductivity of AgNWs. In this study, I have mainly studied synthesis of silver nanowire and their application such as transparent electrode and stretchable electrode. The research results suggest that high performance transparent electrode using silver nanowire can be demonstrated and fabrication stretchable electrode can be a step toward producing intelligent and multi-functional soft electric devices as friendly human / electronics interface, and it may ultimately contribute to the applications in wearable computers.
Advisors
Lee, Seung S.researcher이승섭researcher
Description
한국과학기술원 :기계공학전공,
Publisher
한국과학기술원
Issue Date
2015
Identifier
325007
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 기계공학전공, 2015.2 ,[viii, 105 p. :]

Keywords

Silver nanowire; Successive multi-step growth method; Flexible electronicsv; Stretchable electronics; Transparent electrode; 은 나노와이어; 연속 성장 공정; 유연 소자; 신축 소자; 투명 전극

URI
http://hdl.handle.net/10203/221075
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=657541&flag=dissertation
Appears in Collection
ME-Theses_Ph.D.(박사논문)
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