Environmentally Friendly Graphene Inks for Touch Screen Sensors

Abstract

Graphene‐based materials have attracted significant attention in many technological fields, but scaling up graphene‐based technologies still faces substantial challenges. High‐throughput top‐down methods generally require hazardous, toxic, and high‐boiling‐point solvents. Here, an efficient and inexpensive strategy is proposed to produce graphene dispersions by liquid‐phase exfoliation (LPE) through a combination of shear‐mixing (SM) and tip sonication (TS) techniques, yielding highly concentrated graphene inks compatible with spray coating. The quality of graphene flakes (e.g., lateral size and thickness) and their concentration in the dispersions are compared using different spectroscopic and microscopy techniques. Several approaches (individual SM and TS, and their combination) are tested in three solvents (N‐methyl‐2‐pyrrolidone, dimethylformamide, and cyrene). Interestingly, the combination of SM and TS in cyrene yields high‐quality graphene dispersions, overcoming the environmental issues linked to the other two solvents. Starting from the cyrene dispersion, a graphene‐based ink is prepared to spray‐coat flexible electrodes and assemble a touch screen prototype. The electrodes feature a low sheet resistance (290 Ω □−1) and high optical transmittance (78%), which provide the prototype with a high signal‐to‐noise ratio (14 dB) and multi‐touch functionality (up to four simultaneous touches). These results illustrate a potential pathway toward the integration of LPE‐graphene in commercial flexible electronics.

Green Solvents for the Liquid Phase Exfoliation Production of Graphene: The Promising Case of Cyrene

“…They embedded such electrodes in a working prototype of a multi-touch screen with a high signal-to-noise ratio (14 dB). These results illustrate a potential pathway toward the integration of LPE-graphene in commercial flexible electronics ( Tkachev, 2021 ). Hassan et al proposed a green ink combining Cyrene and ethyl cellulose (polymeric binder that helps lowering sheet resistance by enhancing connectivity and filling the gaps).…”

“…, tip-sonication and high-shear mixing). The authors produced highly concentrated dispersions (up to 3.70 g L −1 ) of few-layer graphene flakes (three to five layers) with mean lateral size of ∼200 nm ( Tkachev, 2021 ). Pan et al developed an environmentally friendly, sustainable, low-cost graphene-based ink in Cyrene with concentration up to 10 mg ml −1 , by using sonication assisted exfoliation.…”

Functional Ink Formulation for Printing and Coating of Graphene and Other 2D Materials: Challenges and Solutions

“…The obvious differences are related to the environmental issue (selection of solvent), yield, and size distribution of nanosheets. [34] Figure 3. a) i) On the left, the coffee-ring effect is schematically depicted and, on the right, the digital image of a dried droplet of several inks with different carrier solvent are shown; ii.…”

A double-layered liquid metal-based electrochemical sensing system on fabric as a wearable detector for glucose in sweat

“…These studies have applied and verified the functions of biosensors by implementing conductive circuits on fabrics. However, it is still challenging to fabricate complex circuits directly on fabric using common electrical inks, such as nano-copper 15 , nano-silver 16 , nano-gold 17 , and graphite ink 18 for printing. This is mostly because the intersecting circuits require multilayer interconnection, which is difficult to achieve on fabrics with these conductive inks.…”