A Universal Approach for Room‐Temperature Printing and Coating of 2D Materials

Abstract

or solvent mixture) which can be further processed into a printable or coatable ink. The behavior of these suspensions is often described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, [3] which implies that the concentration of the nanosheets in the suspensions has an upper limit above which the suspension becomes unstable. [4] Nevertheless, highconcentration suspensions (inks) are necessary for the formation of percolated particle networks, [5] and fulfilling the rheological requirements of high-throughput printing and coating methods (e.g., high viscosity). Regardless of their concentration, suspensions are thermodynamically unstable, and particles tend to reduce their surface energy by aggregation. [6] To lower the rate of sedimentation, the surface energy difference between the solvent and the 2D material must be minimized, [3] which limits the choices of the dispersionmedia to a few solvents whose solubility envelope may not be suitable for subsequent processing. In conventional ink formulations, additives such as surfactants, binders, and rheology modifiers are used to address the aforementioned problems and process the 2D material suspensions into printable or coatable inks. [7][8][9][10] For instance, large concentrations of polymeric binders (e.g., 70 mg mL −1 cellulose acetate butyrate) are needed to increase the viscosity of graphene inks to a level that is suitable for screen printing. [11] Since typical additives adversely affect the electronic properties (e.g., Processing 2D materials into printable or coatable inks for the fabrication of functional devices has proven to be quite difficult. Additives are often used in large concentrations to address the processing challenges, but they drastically degrade the electronic properties of the materials. To remove the additives a high-temperature post-deposition treatment can be used, but this complicates the fabrication process and limits the choice of materials (i.e., no heat-sensitive materials). In this work, by exploiting the unique properties of 2D materials, a universal strategy for the formulation of additive-free inks is developed, in which the roles of the additives are taken over by van der Waals (vdW) interactions. In this new class of inks, which is termed "vdW inks", solvents are dispersed within the interconnected network of 2D materials, minimizing the dispersibility-related limitations on solvent selection. Furthermore, flow behavior of the inks and mechanical properties of the resultant films are mainly controlled by the interflake vdW attractions. The structure of the vdW inks, their rheological properties, and film-formation behavior are discussed in detail. Large-scale production and formulation of the vdW inks for major high-throughput printing and coating methods, as well as their application for room-temperature fabrication of functional films/devices are demonstrated.

All inkjet-printed electronics based on electrochemically exfoliated two-dimensional metal, semiconductor, and dielectric

“…The μ and I on /I off values are much higher compared to previously reported FETs based on printed TMDC nanosheet channels (Fig. 6f) 36,38,[40][41][42]79 . Furthermore, the device performance was even better than the TFSI-treated top-contact MoS 2 FETs on spin-coated HfO 2 layers (average μ and I on /I off were 1.3 cm 2 V −1 s −1 and 9.7 × 10 4 at V D = 1 V, while the SD values were 0.69 cm 2 V −1 s −1 and 6.1 × 10 4 ) (Supplementary Fig.…”

Structured Ultra‐Flyweight Aerogels by Interfacial Complexation: Self‐Assembly Enabling Multiscale Designs

“…This can be considered as a great advantage over direct ink writing of suspensions containing rheological modifiers (e.g., polymer), as they suffer from deformation and/or cracking induced by thermal stresses due to thermal expansion coefficient mismatch. [31] Figure 4. a) Digital image of reduced WUFA supported by the hair of an "old man" cactus.…”

“…However, these additives dramatically diminish the properties of the final products (conductivity, for example) and increase the density of the resultant aerogels. [31] To surmount the main challenges in processing and property development, we introduce a facile method to develop a new type of two-phase soft materials with tunable morphology, enabling the design of UFAs with controlled macroscale. This was accomplished by microfluidic extrusion of low-concentration aqueous GO suspensions in different nonpolar phases containing a surfactant.…”

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

“…Blade coating [25] Graphene Application: Printed Electronics Slot-die coating [6] Graphene conc. : 0.…”