Biaxially Stretchable Transparent Conductors That Use Metallic Single-Walled Carbon Nanotube Films
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Biaxially Stretchable Transparent Conductors That Use Metallic Single-Walled Carbon Nanotube Films Xinning Ho1, Ju Nie Tey1, Wenjun Liu2, Chek Kweng Cheng1 and Jun Wei1 1 2
Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075 School of EEE, Nanyang Technological University, Nanyang Avenue, Singapore 639798
ABSTRACT Transparent electronic devices that retain their electrical properties upon stretching and twisting are envisioned to be used in transparent wearable electronics and stretchable displays. An integral part of stretchable transparent electronic devices is the stretchable transparent conductor. In this work, we demonstrate biaxially stretchable transparent conductors that use metallic single-walled carbon nanotube films. Two dimensionally buckled metallic single-walled carbon nanotube films are realized. The “wavy” film “flattens out” when stretched and its electrical resistance hardly changes up to 3% applied strain. A similar film without any buckled structures suffers a severe degradation in electrical conductivity. Besides exhibiting stretchability, these transparent conductors display good sheet resistance (down to 3 kΩ/□) and transmittance (~ 80% at a wavelength of 550 nm). INTRODUCTION Electronic devices that can be stretched, bent and folded without degradation of their electrical properties provide exciting opportunities for novel applications such as wearable electronics, electronic implants, stretchable displays and artificial muscles[1-10]. Much work has been done on stretchable conductors because they form the basis for any stretchable electronic device. Carbon nanotubes (CNTs), with high aspect ratio, high electrical conductivity and superb mechanical robustness, have long been considered to be a promising material. Besides their superior electrical and mechanical properties, thin layers of carbon nanotubes are optically transparent. Hence, they are promising for fabricating stretchable transparent conductors, which are likely to be useful in niche applications, such as invisible wearable electronics or stretchable displays. Various groups have explored the development of CNT based stretchable conductors[1024] . A common method to fabricate CNT-based stretchable conductor is to embed CNTs in elastic polymers[10-20]. In one instance, rubber-like conductive composites were developed by mixing CNTs with an ionic liquid and a fluorinated copolymer[11]. Shin et al. infiltrated CNT forests with a polyurethane (PU) solution[12]. Many groups embedded CNTs in various formats (i.e. CNT forests, CNT networks, aligned CNT ribbons) in poly(dimethylsiloxane) (PDMS)[13-20]. These approaches are limited in success because they require a high loading of CNTs to achieve high electrical conductivity. A high loading of CNTs increases the elastic modulus (i.e. stiffness) of the CNT composites and decreases the stretchability. The transparency is also compromised.
Another technique used to fabricate CNT-based stretchable conductor is to create wavy structures of CNTs on an elastic
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