Inkjet printing of graphene

Abstract

The inkjet printing of graphene is a cost-effective, and versatile deposition technique for both transparent and non-transparent conductive films. Printing graphene on paper is aimed at low-end, high-volume applications, i.e., in electromagnetic shielding, photovoltaics or, e.g., as a replacement for the metal in antennas of radio-frequency identification devices, thereby improving their recyclability and biocompatibility. Here, we present a comparison of two graphene inks, one prepared by the solubilization of expanded graphite in the presence of a surface active polymer, and the other by covalent graphene functionalization followed by redispersion in a solvent but without a surfactant. The non-oxidative functionalization of graphite in the form of a donortype graphite intercalation compound was carried out by a Birch-type alkylation, where graphene can be viewed as a macrocarbanion. To increase the amount of functionalization we employed a graphite precursor with a high edge to bulk carbon ratio, thus, allowing us to achieve up to six weight percent of functional groups. The functionalized graphene can be readily dispersed at concentrations of up to 3 mg ml À1 in non-toxic organic solvents, and is colloidally stable for more than 2 months. The two inks are readily inkjet printable with good to satisfactory spreading.Analysis of the sheet resistance of the deposited films demonstrated that the inks based on expanded graphite outperform the functionalized graphene inks, possibly due to the significantly larger graphene sheet size in the former, which minimizes the number of sheet-to-sheet contacts along the conductive path. We found that the sheet resistance of printed large-area films decreased with an increase of the number of printed layers. Conductivity levels reached approximately 1-2 kU , À1 for 15 printing passes, which roughly equals a film thickness of 800 nm for expanded graphite based inks, and 2 MU , À1 for 15 printing passes of functionalized graphene, having a film thickness of 900 nm. Our results show that ink preparation and inkjet printing of graphene-based inks is simple and efficient, and therefore has a high potential to compete with other conductive ink formulations for large-area printing of conductive films.

Conductivity Enhancement of Binder‐Based Graphene Inks by Photonic Annealing and Subsequent Compression Rolling

“…The presence of a binder with a glass transition point above room temperature may lower the particle mobility even under high force applied, obstruct sheet-to-sheet interactions, and thereby render the application of compression rolling inefficient. Nevertheless, taking into account the two main aspects of performance an ink should provide, i.e., good printability with high printing definition and sufficiently low sheet resistance, e.g., less than 5 Ω & À1 , it becomes clear from previous works [16,[18][19][20]22,25,26,[28][29][30] that the use of a binder, surfactant, or rheology modifier is necessary. These rheological modifications should be compatible with the commonly used R2R-friendly flexible substrates and comply with already existing high-speed technologies.…”

“…[11][12][13] Even though the field of printable conductors is still mainly focused on metalbased (Ag, Cu, %50 mΩ & À1 at 25 mm thickness) [13,14] inks and PEDOT:PSS dispersions (%50 Ω & À1 ), [15] graphene-based conductive inks are gaining attention both from science [16][17][18][19][20][21][22][23][24] and technology. [25] Unfortunately, the conductive properties of graphene inks and printed structures thereof are still far from being a replacement for silver and copper inks.…”

Conductive Screen Printing Inks by Gelation of Graphene Dispersions

“…[ 37 ] In contrast, expanded graphite (EG) demonstrates much better dispersibility than graphite due to signifi cantly weakened van der Waals interactions on account of an increased distance between the layers. [ 13,[38][39][40] This results in much shorter times and smaller energy input to obtain well-exfoliated concentrated dispersions of typically large (>1 µm) fl ake graphene. [ 39,41 ] Colloidal stability, however, as for the exfoliation of graphite, requires the presence of surface active agents and can be adjusted accordingly.…”

“…For example, ink annealing at 250 °C and higher for 30 min [ 18,24,25 ] signifi cantly limits the range of suitable substrates and fundamentally limits high speed R2R industrial realization. Thus, the design of graphene inks that meet the requirements of current R2R applications is still to be accomplished.There are several reports on the preparation of graphene-based inks comprising either graphene oxide (GO), [ 17,19,23,[27][28][29][30] or graphite exfoliated with [ 13,16,18,22,24,25 ] and without [ 20 ] surface active agents. The preparation of inks based on GO is relatively simple.…”

A simple and flexible route to large-area conductive transparent graphene thin-films

“…of isopropanol and propylene glycol is the optimum to uniformly disperse graphene at a concentration of 0.1 mg/ml and use for thin film self-assembly. The colloidally stable (>1 month), non-toxic and water-miscible dispersions can be utilized not only for thin film self-assembly but also for the formulation of conductive paints and inks [64]. Independent of utilizing donor-or acceptor-type intermediates, thermally annealed thin films performed equally well in terms of sheet resistance and transmittance.…”