Stretchable Transparent Conductors Research Articles

Stretchable Transparent Conductors: from Micro/Macromechanics to Applications.

Stretchable transparent conductors (STCs), generally consisting of conducting networks and stretchable transparent elastomers, can maintain stable conductivity and transparency even at large tensile strain, beyond the reach of rigid/flexible transparent conductors. They are essential components in stretchable/wearable electronics for using on irregular 3D conformable surfaces and have attracted tremendous attention in recent years. This review aims to provide systematical correlation of the conducting element-substrate interaction with the structural stability of conducting networks, as well as the properties and device applications of STCs. It starts with the micromechanics for stretching of conducting elements on substrates, including the mechanical mismatch, distribution/level of interfacial shear stress, and the deformation behavior of conducting elements on substrates. The macromechanics for stretching of conducting networks on substrates are then further illustrated from a more statistical point of view, namely sliding/preferred orientation of percolation networks, unfolding of buckled structures, and unit cell distortion/distributed rupture of nanomeshes. The structure-dependent properties as well as the state-of-the-art applications of STCs are summarized before ending with the conclusions and outlooks for STCs.

Three-Dimensional Stretchable and Transparent Conductors with Controllable Strain-Distribution Based on Template-Assisted Transfer Printing.

Although stretchable transparent conductors, stemmed from the strategies of both conductive composite and structural design of nonstretchable conductors, have been extensively studied, these conductors either suffer from low stretchability or require a complex fabrication process, which drastically limits their practical applications. Here, we propose a novel strategy combining the design of substrates and a simple template-assisted transfer printing process to fabricate three-dimensional (3D) transparent conductors. The strategy not only eliminates the complex and costly fabrication processes but it also endows conductors with high stretchability and long-term stability, thanks to the controllable strain distribution as well as the seamless connection between the conductor layer and the substrate. These newly designed 3D conductors achieve a low sheet resistance of 1.0 Ω/sq with a high transmittance of above 85% and remain stable without obvious resistance change during 1000 stretching-relaxation cycles until 60% strain, which are superior to most reported conductors. A large-area stretchable heater based on the 3D conductor realizes the temperature fluctuation below 10% even under a large strain, thus showing huge application prospects in the field of wearable healthcare electronics. The simple solution-processed fabrication method and high performance such as stretchability and low resistance change over a large strain range promote the practical applications of these newly designed 3D conductors.

Solution‐Grown Serpentine Silver Nanofiber Meshes for Stretchable Transparent Conductors

AbstractMetal fiber nanomeshes, fabricated by depositing metals on the electrospun nanofiber templates, have come into the spotlight as promising stretchable transparent conductors. However, most currently stretchable metal fibers are produced via expensive vacuum deposition methods. This work reports a low‐cost approach to prepare transparent, conducting, and serpentine silver nanofiber mesh elastomers (SNME). The key of forming SNME is buckling the electrospun polymer nanofiber templates into wavy structure and subsequently electrolessly depositing silver on the templates. Optoelectronic performance of the SNME is elaborately optimized by tuning the number of Ag nanoseeds and the electroless deposition time. The resulting SNME exhibit a high visible light transmittance of 81%, a low sheet resistance of 9.2 Ω sq−1, and an excellent stretchability with 2.4‐times of resistance increases after repeated stretching to 70% for 1000 cycles. In situ observations indicate that the SNME are capable of straightening and rearranging to adapt to the tensile deformation. Its application potential as an ideal platform for fabricating intelligent interfaces is demonstrated by using the SNME as a wearable resistance sensor which can monitor finger joint motions.

A High Aspect Ratio Serpentine Structure for Use As a Strain-Insensitive, Stretchable Transparent Conductor.

The development of strain-insensitive stretchable transparent conductors (TCs) is essential for manufacturing stretchable electronics. Despite recent progress, achieving a high optoelectronic performance under applied strain of 50% continues to present a significant challenge in this research field. Herein, an ultratall and ultrathin high aspect ratio serpentine metal structure is described that exhibits a remarkable stretching ability (the resistance remains constant under applied strain of 100%) and simultaneously provides an excellent transparent conducting performance (with a sheet resistance of 7.6 Ω -1 and a transmittance of 90.5%). It is demonstrated that the highly stretchable transparent conducting properties can be attributed to the high aspect ratio feature. A high aspect ratio (aspect ratio of 17-367) structure permits facile deformation of the serpentine structure with in-plane motion, leading to a high stretching ability. In addition, this structural feature avoids the classic tradeoff between optical transmittance and electrical conductance, providing a high electrical conductance without decreasing the optical transmittance. The practical utility of these devices is tested by using these TCs as stretchable interconnectors among LEDs or in wearable VOC gas sensors.

Deformable and Transparent Ionic and Electronic Conductors for Soft Energy Devices

AbstractThe recent boom in deformable or stretchable electronics, flexible transparent displays/screens, and their integration into the human body has facilitated the development of multifunctional energy devices that are stretchable, transparent, wearable, and/or biocompatible while meeting the energy or power requirements. The development of soft energy systems begins with the preparation of relevant conductors and the design of innovative device configurations. In this study, recent advances and trends in stretchable and transparent electronic and ionic conductors are reviewed coupled with the growing efforts to use them for soft energy storage and conversion systems. Stretchable transparent ionic conductors present possibilities for use as current collectors and electrolytes in soft electronic/energy devices, providing novel insight into biofriendly systems for an effective human–machine interaction. Moreover, representative examples that demonstrate soft energy devices based on stretchable transparent ionic/electronic conductors are discussed in detail. Furthermore, the challenges and perspectives of developing novel stretchable transparent conductors and device configurations with tailored features are also considered.

Silver nanowire network embedded in polydimethylsiloxane as stretchable, transparent, and conductive substrates

ABSTRACTHighly stretchable transparent conductors where Ag nanowire networks (AgNWs) are reliably embedded into a polydimethylsiloxane (PDMS) substrate are presented. In spite of the weak physical and chemical interaction between Ag nanowires and PDMS, a significantly high transfer efficiency and uniform embedding of AgNW percolation mesh electrodes into PDMS was achieved by simply coating aerogels onto the AgNWs and using water‐assisted transfer. By the failure‐free transfer and reliable bonding with the substrate, the conductive PDMS with embedded AgNWs that exhibits a sheet resistance (Rs) of 15 Ω/sq and 80% optical transmittance (T) are reported here. The PDMS films accommodate tensile strains up to 70% and a cyclic strain of 25% for more than 100 cycles, with subsequent Rs values as low as 90 and 27 Ω/sq, respectively. The T of this conductive PDMS is more than 25% higher than that of networks of CNTs, Cu nanowires, and hybrid composites of CNTs and graphene embedded in elastomer films such as PDMS, polyurethane, and Ecoflex. The simple and reproducible fabrication allows the extensive study and optimization of the stretchability of the meanders in terms of humidity, thickness, and substrate. The results provide new insights for designing stretchable electronics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43830.

Biaxially stretchable transparent conductors that use nanowire networks

Abstract

Room‐Temperature Nanosoldering of a Very Long Metal Nanowire Network by Conducting‐Polymer‐Assisted Joining for a Flexible Touch‐Panel Application

AbstractAs an alternative to the brittle and expensive indium tin oxide (ITO) transparent conductor, a very simple, room‐temperature nanosoldering method of Ag nanowire percolation network is developed with conducting polymer to demonstrate highly flexible and even stretchable transparent conductors. The drying conducting polymer on Ag nanowire percolation network is used as a nanosoldering material inducing strong capillary‐force‐assisted stiction of the nanowires to other nanowires or to the substrate to enhance the electrical conductivity, mechanical stability, and adhesion to the substrate of the nanowire percolation network without the conventional high‐temperature annealing step. Highly bendable Ag nanowire/conducting polymer hybrid films with low sheet resistance and high transmittance are demonstrated on a plastic substrate. The fabricated flexible transparent electrode maintains its conductivity over 20 000 cyclic bends and 5 to 10% stretching. Finally, a large area (A4‐size) transparent conductor and a flexible touch panel on a non‐flat surface are fabricated to demonstrate the possibility of cost‐effective mass production as well as the applicability to the unconventional arbitrary soft surfaces. These results suggest that this is an important step toward producing intelligent and multifunctional soft electric devices as friendly human/electronics interface, and it may ultimately contribute to the applications in wearable computers.

Biaxially Stretchable Transparent Conductors That Use Metallic Single-Walled Carbon Nanotube Films

ABSTRACTTransparent 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).