Metal‐Based Flexible Transparent Electrodes: Challenges and Recent Advances

Abstract

nanotubes [CNTs] and graphene), and metal-based materials are superior to ITO in the mechanical flexibility and the potential for roll-to-roll (R2R) manufacture. [16,17] Yet, a common drawback of FTEs made of conducting polymers, CNTs, and graphene is the inferior electrical conductivity. [18][19][20][21][22][23][24] Po l y ( 3 , 4 -e t h y l e n e d i o x y t h i o p h e n e )poly(styrene sulfonate) (PEDOT:PSS) is one of the most widely used conducting polymers. PEDOT:PSS shows the lowest cost among various transparent electrode materials, [25] but the low intrinsic conductivity, poor environmental stability (upon exposure to high temperature, high humidity, or UV irradiation), and self-emission of blue/green tinge limit its applications in flexible optoelectronics. [1,26] Whereas individual CNT and graphene may exhibit excellent conductivity, thin films made of multijunctional assembly of these nanomaterials show high contact resistance at the junctions. [27,28] The surface defects and polycrystallinity of these carbon materials, which are difficult to eliminate, further decrease the conductivity. [28][29][30][31][32][33] On the other hand, metals possess the highest electrical conductivity among all kinds of materials. [34] Thin and surface-structured metal electrodes are optically transparent and mechanically flexible. The combinatorial attributes of high conductivity, tunable transmittance, and engineerable flexibility make metal-based materials the most promising candidates for FTEs. [3,35] To date, there are three major types of metal-based FTEs (m-FTEs), including ultrathin metal films, metal nanowire networks, and metal meshes. Each type of m-FTEs shows unique advantages and critical challenges toward large-scale applications as summarized in Figure 1.This article discusses the characteristics and major challenges of each type of m-FTEs, and reviews their research advances in recent years. It then discusses the ability to achieve scalable production of these m-FTEs from the point of view of materials choice and fabrication technology. Finally, it provides perspectives on the transition from lab study to industry fabrication of m-FTEs in the future. Metal-Based-Flexible Transparent Electrodes Made of Ultrathin Metal FilmsUltrathin and homogeneous metal (such as Ag, Au, Cu, or Al) films with a thickness of 10-20 nm exhibit good electrical Flexible transparent electrodes (FTEs) with high optical transmittance, low sheet resistance, and high flexibility are critical and indispensable components of emerging flexible optoelectronic devices. Indium tin oxide (ITO), the major transparent conductive material used for optoelectronics nowadays, is not suitable for flexible applications because of its brittleness. In the past decade, researchers have developed a wide variety of new transparent conductive materials to replace ITO, among which metal-based FTEs (m-FTEs) including ultrathin metal films, metal nanowire networks, and metal meshes appear to be particularly promising. In this review, the authors summarize ...

Silver Nanowire Networks: Ways to Enhance Their Physical Properties and Stability

“…Metallic nanowires (MNWs) started to be investigated after significant progress in the synthesis of silver nanowires (AgNWs) [1], followed by copper nanowires (CuNWs) [2], as well as copper-nickel nanowires (Cu-Ni NWs) [3] or other bimetallic nanowires [4]. The random networks formed by MNWs show excellent properties in terms of optical transparency and electrical conductivity [5,6]; therefore, they exhibit great potential as transparent electrodes (TE) [7,8] integrated within many devices, such as solar cells [9,10], transparent heaters [11][12][13], organic light-emitting diodes [14], smart windows [15], flexible pressure sensors [16], supercapacitors [17] or touch screens [18]. Moreover, MNW networks have demonstrated promising assets for several applications, not necessarily related to TE, such as antimicrobial activity [19], water purification [20], memristive devices [21] or low-emissivity films [22].…”

Epidermis‐Inspired Wearable Piezoresistive Pressure Sensors Using Reduced Graphene Oxide Self‐Wrapped Copper Nanowire Networks

“…In addition, the CuNW percolation network can effectively tolerate deformation without a significant decay in conductivity. [ 58,72 ] Furthermore, our customized PDMS substrate has good stretchability, as much as 600%, that can accommodate the extra stress during the stretching cycles. As shown in Figure 3h, with the increased strain the CurGONW network structures themselves started to slightly deform and partly ruptured with the increased strain.…”

Flexible transparent electrodes based on metallic micro–nano architectures for perovskite solar cells

“…The flexible TEs based on MMNAs become potential candidates as conductive substrates in flexible electronics. 167,168 The flexibility of TEs is mostly related to three aspects: (1) the flexibility of substrates, 31,166,169 (2) the flexibility of conductive materials, 170 and (3) the adhesion between conductive materials and substrates. 171,172 The flexible substrates including flexible glass and polymer thin films should possess both high optical transmittance and flexibility.…”