Templated Self-Assembly of Ultrathin Gold Nanowires by Nanoimprinting for Transparent Flexible Electronics

Abstract

We fabricated flexible, transparent, and conductive metal grids as transparent conductive materials (TCM) with adjustable properties by direct nanoimprinting of self-assembling colloidal metal nanowires. Ultrathin gold nanowires (diameter below 2 nm) with high mechanical flexibility were confined in a stamp and readily adapted to its features. During drying, the wires self-assembled into dense bundles that percolated throughout the stamp. The high aspect ratio and the bundling yielded continuous, hierarchical superstructures that connected the entire mesh even at low gold contents. A soft sintering step removed the ligand barriers but retained the imprinted structure. The material exhibited high conductivities (sheet resistances down to 29 Ω/sq) and transparencies that could be tuned by changing wire concentration and stamp geometry. We obtained TCMs that are suitable for applications such as touch screens. Mechanical bending tests showed a much higher bending resistance than commercial ITO: conductivity dropped by only 5.6% after 450 bending cycles at a bending radius of 5 mm.

Ultra-Smooth, Fully Solution-Processed Large-Area Transparent Conducting Electrodes for Organic Devices

“…It is possible to improve the conductivity of TCEs through the use of metallic materials such as metal nanowires (NWs) and metal nano-mesh/micro-mesh materials1314. Recently, metal NWs, such as silver NWs, copper NWs, and gold NWs, have shown promise as alternative TCEs due to their high conductivities, transparency, and excellent flexibility151617. However, metal NW-based TCEs typically possess high surface roughness due to interconnections between their junctions; the materials are also easily oxidized in air, often degrading the performance of optoelectronic devices1819.…”

“…Metal micro- and nano-mesh electrodes have attracted considerable attention recently because the thickness, spacing, and line-widths of metal patterns can be easily modified to obtain desirable optical and electrical properties with the benefit of air-processable conditions. These metal meshes have been fabricated by various methods such as pattern-masked evaporation2021, nanoimprint lithography172223, inkjet24, flexographic25, transfer2627 and gravure-offset printing1228. However, these electrodes also suffer from high surface roughness, resulting in the possibility of electrical short-circuits between the TCEs and the top electrode.…”

Carrier Dynamics in Ultrathin Gold Nanowires: Role of Auger Processes

“…Our experiments together with the rate equation model gives an estimate of the Auger coefficient k −1 A and the phonon mediated carrier relaxation rate in Au-UNWs. The results are of potential importance for devices and sensors based on Au-UNWs whose performance depends on the electron dynamics in nano-gold [10,11,13].…”

Direct Nanoimprinting of a Colloidal Self‐Organizing Nanowire Ink for Flexible, Transparent Electrodes

“…The ink is optimized to follow the structures imposed by the printing process. We recently introduced an ink that takes a more active part: dispersed nanowires self‐organize into hierarchical superstructures during imprinting and guarantee the formation of a percolating mesh . The wires have an aspect ratio exceeding 1000 and are flexible enough to follow microscale features of an elastomeric stamp.…”

“…The geometry of the structuring template is faithfully reproduced and supplemented by a structure that depends on the wires' interactions. Line contacts between the wires induce the formation of well‐defined bundles of parallel wires that accumulate all metal content; the wires' concentration ultimately sets the width of lines formed inside the stamp . The wires interdigitate inside the bundles like wool fibers in a yarn, ensuring percolation over macroscopic distances even at relatively low ink concentrations.…”