Transparent Electrodes Printed with Nanocrystal Inks for Flexible Smart Devices.

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

Electrochromism refers to the phenomenon where optical changes in a material occur during electrochemical reactions under an applied voltage. Because of advantages such as high contrast and low operating voltage, electrochromic (EC) devices have been widely used in smart windows, switchable mirrors, optical shutters, and information displays.Such devices are usually fabricated on a rigid glass substrate to permit their use in automobile and building applications, which require long-term stability under climatic conditions. However, the use of soft polymer or textile substrates has increased the versatility of such technology, allowing the fabrication of novel flexible, stretchable, and wearable EC devices. Since the first flexible EC devices using WO3layers were developed in 1995 a wide variety of inorganic and organic materials has been investigated with respect to their compatibility with flexible substrates. However, most EC devices fabricated using these materials showed poor performances, especially in terms of coloration speed and long-term stability, which was mainly due to the electrical and mechanical properties of the flexible substrate. In addition, the large area and cost-effective roll-to-roll (RTR) coating process for transparent electrodes has been demonstrated for the fabrication of low cost flexible EC devices. To date, the most common transparent electrode for EC devices is indium-tin-oxide (ITO) due to its low resistivity, high transparency, and mature mass production via processes such as sputtering. Amorphous ITO(a -ITO) films can easily be coated on a flexible substrate using conventional DC sputtering at ambient temperatures, but the high sheet resistance and brittleness of thick a-ITO films prevents their use for flexible and transparent EC devices. Oxide-metal-oxide(OMO) multilayer films have been extensively reported in flexible optoelectronic devices as an alternative to a-ITOfilms. However, there are few reports regarding flexible and transparent EC devices fabricated using OMO multilayer electrodes. The development of a conductive layer with high electrical conductivity and stable mechanical flexibility is greatly needed for flexible EC device applications. In this paper, we report the electrochromic properties of poly(3-hexylthiophene) (P3HT) films coated on ITO/Ag/ITO (IAI) multilayers deposited on flexible PET substrates using an ambient temperature RTR sputtering system. By continuous sputtering of ITO/Ag/ITO layers on the flexible PET substrate, we realized highly transparent, flexible, and conductive electrodes for flexible and transparent EC devices. We characterized the coloration efficiency, response time, and long-term stability of the P3HT on the flexible substrate compared to the material prepared on glass substrates.

Manipulation of mechanical properties of monolayer molybdenum disulfide: Kirigami and hetero-structure based approach

In recent years, the demand for digital transformation (DX) in the industrial sector has been extremely high. In response to this high demand, a variety of smart devices have been invented and offered. Especially in the research field, flexible or bendable smart devices have been devised by using thin-film polymers such as polyimide and parylene as substrates. Micro/nanofabrication is a fundamental technology in the research and development of these smart devices. The presenter's laboratory has conducted research on flexible smart devices for social implementation based on micro/nanofabrication. Based on the knowledge obtained from flexible smart devices, we have also studied stretchable devices, which are expected to be the next generation of smart devices. In this presentation, we report an overview of our research on flexible smart devices and stretchable systems. In particular, we present our research on flexible smart devices and the development of smart devices for use in medical and animal experiments. In addition, research on stretchable sensors using liquid metal and stretchable systems are reported. Stretchable devices based on micro- and nano-fabrication might be further accelerated toward social implementation in the future.

Stretchable electronic devices with intrinsically stretchable components have significant inherent advantages, including simple fabrication processes, a high integrity of the stacked layers, and low cost in comparison with stretchable electronic devices based on non-stretchable components. The research in this field has focused on developing new intrinsically stretchable components for conductors, semiconductors, and insulators. New methodologies and fabrication processes have been developed to fabricate stretchable devices with intrinsically stretchable components. The latest successful examples of stretchable conductors for applications in interconnections, electrodes, and piezoresistive devices are reviewed here. Stretchable conductors can be used for electrode or sensor applications depending on the electrical properties of the stretchable conductors under mechanical strain. A detailed overview of the recent progress in stretchable semiconductors, stretchable insulators, and other novel stretchable materials is also given, along with a discussion of the associated technological innovations and challenges. Stretchable electronic devices with intrinsically stretchable components such as field-effect transistors (FETs), photodetectors, light-emitting diodes (LEDs), electronic skins, and energy harvesters are also described and a new strategy for development of stretchable electronic devices is discussed. Conclusions and future prospects for the development of stretchable electronic devices with intrinsically stretchable components are discussed.

Fabrication of self-recoverable flexible and stretchable electronic devices

Metal nanowires, particularly silver nanowires (AgNWs), have been extensively used in transparent electrodes and substrates requiring high optical transmittance, as well as in flexible and stretchable electronic devices, owing to their intrinsic material properties. These include the ability to maintain electrical conductivity under mechanical deformation. The optical/electrical performance of such systems is primarily governed by the percolation behavior among individual nanowires within a two-dimensional (2D) conductive network. In this study, we propose a theoretical approach to elucidate the relationship between sheet resistance and optical transmittance of AgNW networks, as a function of nanowire dimensions and network density. Furthermore, considering the broad application of AgNWs in stretchable electrodes, we present a model to predict changes in sheet resistance and optical transmittance under uniaxial/biaxial strain, assuming an ideal elastic substrate. The proposed model offers design guidelines for optimizing the optical and electrical properties of AgNW-based stretchable conductors.

Flexible optoelectronic devices have a broad application prospect in the field of wearable electronic devices, among which the superior transparent electrode is the core problem in achieving high-performance flexible optoelectronic devices. The brittle indium tin oxide (ITO) transparent electrode, which is currently commonly used, is difficult to be compatible with the flexible substrate. Multilayer dielectric/metal/dielectric (DMD) structure films are attracting attention as next-generation ITO-free electrodes. High optical transmittance, super electrical conductivity, and mechanical flexibility of DMD electrodes make them promising for highly efficient optoelectronic devices. Despite substantial research on the optimization of DMD electrodes, a large gulf still exists in obtaining foldable and transparent conductive electrodes and applying them to light-emitting devices, including organic light-emitting diodes (LEDs), quantum dot LEDs, and perovskite LEDs. In this perspective, we review the superiority of DMD electrodes in terms of optical and electrical performance, and mechanical flexibility, and summarize their applications in LEDs. Furthermore, we also give future research directions for DMD electrodes regarding physical properties, mechanism stability, and application reliability.

In recent years, flexible electronic devices have become a hot topic of scientific research. These flexible devices are the basis of flexible circuits, flexible batteries, flexible displays and electronic skins. Graphene-based materials are very promising for flexible electronic devices, due to their high mobility, high elasticity, a tunable band gap, quantum electronic transport and high mechanical strength. In this article, we review the recent progress of the fabrication process and the applications of graphene-based electronic devices, including thermal acoustic devices, thermal rectifiers, graphene-based nanogenerators, pressure sensors and graphene-based light-emitting diodes. In summary, although there are still a lot of challenges needing to be solved, graphene-based materials are very promising for various flexible device applications in the future.

Intrinsically stretchable conjugated polymer semiconductors in field effect transistors

Wax-shaped wettability assisted patterning of silver nanowires on various substrates as transparent, flexible, or stretchable electrodes

Marangoni-flow-assisted assembly of single-walled carbon nanotube films for human motion sensing

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), a type of conducting polymer has caught lots of attraction from scientists for its excellent properties as low-cost, non-toxic, etc. This also is a potential material for various applications as transparent electrodes, flexible and stretchable devices, thus improving the electrical properties of this polymer plays an important role. Among various methods such as post-treatment, doping with glycerol, and d-sorbitol herein, DMSO was chosen as an additive to enhance the conductivity of PEDOT:PSS. The results, including the increase in the films conductance according to the rise of DMSO dopant ratio from 0 to 2, good transmittance and surface morphology were clearly presented. This will be the platform for the further study of the utilization of PEDOT:PSS in various potential optoelectronic devices in the future.

Origami offers two-dimensional (2D) materials with great potential for applications in flexible electronics, sensors, and smart devices. However, the dynamic process, which is crucial to construct origami, is too fast to be characterized by using state-of-the-art experimental techniques. Here, to understand the dynamics and kinetics at the atomic level, we explore the edge effects, structural and energy evolution during the origami process of an elliptical graphene nano-island (GNI) on a highly ordered pyrolytic graphite (HOPG) substrate by employing steered molecular dynamics simulations. The results reveal that a sharper armchair edge is much easier to be lifted up and realize origami than a blunt zigzag edge. The potential energy of the GNI increases at the lifting-up stage, reaches the maximum at the beginning of the bending stage, decreases with the formation of van der Waals overlap, and finally reaches an energy minimum at a half-folded configuration. The unfolding barriers of elliptical GNIs with different lengths of major axis show that the major axis should be larger than 242 Å to achieve a stable single-folded structure at room temperature. These findings pave the way for pursuing other 2D material origami and preparing origami-based nanodevices.

Flexible optoelectronic devices have attracted enormous attention as an essential component in next‐generation wearable devices. To meet the trend of biocompatibility, flexibility and low cost, paper‐based optoelectronic devices have become compelling candidates. Moreover, 2D organic–inorganic metal halide perovskites have been extensively studied for the application in flexible optoelectronic devices owing to their long‐term moisture stability, optoelectronic tunability, and multiple quantum well (MQW) structures. Herein, the paper‐based flexible optoelectronic devices are designed by spin‐coating PEDOT:PSS and (iso‐BA)2MAn‐1PbnI3n+1 (n ≥ 1) on regular filter paper with responsivity of 2.62 mA W−1 and response time (τrise/τdecay) of 0.81/0.18 s at 35% relative humidity (RH). Furthermore, the responsivity may be increased by 250% within the humidity range from 35% to 90%, and remains above 92% of the initial value after measured for 1800 s at 60% RH. This work can pave the way for further studies about the humidity effect on perovskites for next‐generation green wearable electronics.