Facile Fabrication of Ultraflexible Transparent Electrodes Using Embedded Copper Networks for Wearable Pressure Sensors

Abstract

Considerable efforts have been made to explore flexible TEs in recent decades. Emerging candidates include conducting polymers, [6] carbon nanotubes, [7] graphene, [8] metal networks, [9][10][11][12] and hybrids of such materials. [13][14][15] Among these, metal networks are widely accepted to be the most promising candidate materials in terms of their high electrical conductivity and mechanical flexibility. Metal networks can be prepared by depositing metals on sacrificial network templates, such as crack networks [9,13] and electrospun fiber meshes. [16,17] Physical vapor deposition methods, including evaporation and sputtering, are most widely used to deposit metals onto these templates. [18][19][20][21] For example, Kulkarni's group has demonstrated a high-performance flexible capacitive touch panel made of thermalevaporated Cu networks. [21] Recently, solution-grown metal network TEs have drawn attention owing to their low cost and scalability. [12,[22][23][24][25][26][27][28] Despite that the crack network templates have the advantages of easy preparation and absence of junctions, there are currently a few simple solution-based processing approaches for fabricating metallic cracking network TEs with low sheet resistance and high visible transparency. The main difficulty lies in the fact that the crack templates are usually water soluble and easily peel off from the supporting substrates, which damaged the crack template and consequently considerably reduced the transmittance since the plating precursor solution tends to dissolve away or permeate the template. On the other hand, a few efforts have devoted to studying the variation of electrical properties of metal networks fabricated by crack template under large mechanical deformation.Here, we have developed a practical strategy for fabricating solution-processed Cu crack network TEs by oxygen plasma treatment-assisted crack template and electroplating (Scheme 1). The critical step that distinguishes this process from normal electroplating deposition is the surface modification of the conducting ITO glass by a simple and broadly applicable oxygen plasma treatment. The crack network templates and Cu wires formed without this treatment exhibited nonuniform and broaden morphologies. In contrast, this treatment resulted in narrow crack templates with good adhesion to the ITO glass, Pressure sensors are in urgent need due to the explosive demands in electronic skins. However, current resistive-type pressure sensors require electrode materials with complex multilevel microstructures or low opacity. Herein, a Cu network transparent electrode (TE) embedded in the polydimethylsiloxane (PDMS) substrate is designed to realize wearable pressure sensor. The Cu network is fabricated by oxygen plasma treatmentassisted crack template and electroplating. The oxygen plasma treatment improves the surface adhesion force of the substrate, which suppresses uneven template cracking and prevents the electroplating solution from seeping under the templates, thereby resulting in 20 ...

Patterning Metal Grids for GaAs Solar Cells with Cracked Film Lithography: Quantifying the Cost/Performance Tradeoff

“…Previous researchers demonstrated CFL grids with 98% transmittance, , although those results used physical vapor deposited metal and glass substrates, which is a substantial departure from the present case. In this work, we used GaAs thin-film stacks that were far more hydrophobic than glass, and surface energy affects cracking behavior. , Aqueous polystyrene suspensions have superior transmittance; however, we could not use them because they wetted the hydrophobic surface too poorly to produce uniform crack templates. Therefore, we used PMMA nanoparticle suspensions with an isopropyl alcohol solvent, which had more favorable surface energetics.…”

“…In this work, we used GaAs thin-film stacks that were far more hydrophobic than glass, and surface energy affects cracking behavior. 19,31 Aqueous polystyrene suspensions have superior transmittance; 19 however, we could not use them because they wetted the hydrophobic surface too poorly to produce uniform crack templates. Therefore, we used PMMA nanoparticle suspensions 8 with an isopropyl alcohol solvent, 32 which had more favorable surface energetics.…”

Metal‐Based Flexible Transparent Electrodes: Challenges and Recent Advances

“…Furthermore, the solar cell based on the Ag mesh electrode exhibited excellent mechanical flexibility during the bending test. [140] Apart from periodically patterned metal meshes, randomly patterned metal meshes fabricated via low-cost processes, such as self-forming crack lithography, [142][143][144][145][146][147] nanosphere lithography, [148][149][150] coffee-ring lithography, [151,152] grain boundary lithography, [120] electrospinning template, [153][154][155][156] and bioinspired template [5,157] are of great interests in recent years. Han et al introduced bio-inspired metal mesh-based TEs based on leaf venation and spider web (Figure 4c).…”

Soft Electronics for the Skin: From Health Monitors to Human–Machine Interfaces

“…[34] In addition to imparting flexibility to electronic devices, they also require mechanical stretchability to better interface and concurrently deform with the skin. Two strategies have been applied to achieve mechanical stretchability in soft electronics: 1) utilizing intrinsically stretchable, rubbery materials including rubbery electronic materials (semiconductors, conductors, and dielectrics) [14,15,24,[35][36][37][38][39][40][41][42][43][44][45] and liquid metals [46][47][48][49] to build the electronics; 2) employing engineered structures like wrinkles, [34,[50][51][52][53][54][55][56] serpentines, [12,17,33,44,[57][58][59][60][61] island-bridge structures, [62,63] textiles, [64] origami, [65,66] kirigami, [37,67] and microcracks [68] to accommodate the induced strain. [30,…”