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

Abstract

The properties of 2D materials are unparalleled when compared to their 3D counterparts; many of these properties are a consequence of their size reduction to only a couple of atomic layers. Metallic, semiconducting, and insulating types can be found and form a platform for a new generation of devices. Among the possible methods to utilize 2D materials, functional printing has emerged as a strong contender because inks can be directly formulated from dispersions obtained by liquid‐phase exfoliation. Printed graphene‐based devices are shifting from laboratory applications toward real‐world and mass‐producible systems going hand in hand with a good understanding of suitable exfoliation methods for the targeted type of ink. Such a clear picture does not yet exist for hexagonal boron nitride (h‐BN), the transition metal dichalcogenides (TMDs), and black phosphorous (BP). Rather, reports of applications of these 2D materials in printed devices are scattered throughout the literature, not yet adding to a comprehensive and full understanding of the relevant parameters. This perspective starts with a summary of the most important features of inks from exfoliated graphene. For h‐BN, the TMDs, and BP, the characteristic properties when exfoliated from solution and strategies to formulate inks are summarized.

Development of Inks with Fillers of NbS3 Quasi-One-Dimensional Charge-Density-Wave Material

“…In printing electronics, the thermophysical properties of the ink and the size of the injecting nozzle are key factors in the formation of proper ink droplets with desirable characteristics. − The droplet formation criteria is determined by the Z -number, Z = ζ ρ a / μ , a dimensionless parameter in which ζ, ρ, and μ are respectively the surface tension, density, and the dynamic viscosity of the ink solution, and a is the diameter of the injecting nozzle. , A Z -number range of 1 ≤ Z ≤ 14 generally results in good droplet formation and its uniform distribution at the intended regions on the substrate . Inks with Z < 1 or Z > 14 result in elongated ligaments or satellite droplet formation which would result in undesirable printing patterns. ,− To tune the properties of our ink, we collected the precipitate part of the liquid-phase exfoliated NbS 3 and transferred it to a secondary solvent of 5 mL of isopropyl alcohol (IPA). The solution underwent a 10 min bath sonication for uniform filler dispersion and to prevent filler agglomeration.…”

“…EG has a higher boiling, and its addition to the IPA-based solution increases the solvent's boiling point. 63,64 The mixing of two solvents with different boiling points and surface tensions prevents the formation of coffee rings which can be explained by the Marangoni effect. 67,68 Figure 4a shows the resultant ink for printing.…”

“…To resolve these issues, an equal volume of ethylene glycol (EG) was added to the IPA solution containing NbS 3 fillers. EG has a higher boiling, and its addition to the IPA-based solution increases the solvent’s boiling point. , The mixing of two solvents with different boiling points and surface tensions prevents the formation of coffee rings which can be explained by the Marangoni effect. , Figure a shows the resultant ink for printing. The produced NbS 3 inks were relatively stable in the air.…”

Highly conductive, conformable ionic laser-induced graphene electrodes for flexible iontronic devices

“…As a result, extensive research has been conducted on flexible electrodes to enhance the performance of iontronic devices 8 . Previous studies have explored various electrode materials 9 – 11 , including Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), carbon nanotubes (CNTs), graphene, and silver nanowires(AgNWs), as well as the incorporation of additives 12 and binders 13 . Additionally, researchers have focused on controlling synthesis and processing methods to ensure optimal electrical and mechanical properties, as well as stable interfaces 14 .…”

Liquid Shear Exfoliation of MoS2: Preparation, Characterization, and NO2-Sensing Properties

“…Although great progress has been made in this field, there are still many challenges regarding the availability of TMD inks and the large-scale fabrication requirements of flexible/wearable devices. In particular, the availability of solution-dispersible TMD nanosheets that can be used to deposit, or print, a large-scale thin film on a variety of non-conventional substrates for the fabrication of TMD-based electronic devices [ 12 , 13 ]. While the sensing properties of MoS 2 nanosheets to various gases have been reported, most of these studies focused on materials mechanically exfoliated [ 14 ], CVD-grown [ 15 ], and sonication-assisted liquid-phase exfoliation methods [ 16 ].…”