A general ink formulation of 2D crystals for wafer-scale inkjet printing

Abstract

Recent advances in inkjet printing of two-dimensional (2D) crystals show great promise for next-generation printed electronics development. Printing nonuniformity, however, results in poor reproducibility in device performance and remains a major impediment to their large-scale manufacturing. At the heart of this challenge lies the coffee-ring effect (CRE), ring-shaped nonuniform deposits formed during postdeposition drying. We present an experimental study of the drying mechanism of a binary solvent ink formulation. We show that Marangoni-enhanced spreading in this formulation inhibits contact line pinning and deforms the droplet shape to naturally suppress the capillary flows that give rise to the CRE. This general formulation supports uniform deposition of 2D crystals and their derivatives, enabling scalable and even wafer-scale device fabrication, moving them closer to industrial-level additive manufacturing.

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“…Thus, it would be a possible technique for formulation ink with ideal purposes like fine resolution printing. However, in the majority of printable inks, external additives (i.e., surfactants [ 45 ] or secondary solvents [ 46 ] ) are usually employed to not only construct a stable colloidal and overcome the coffee‐ring issue and produce a uniform pattern, [ 47 ] but also tune the concentration or rheological properties of an ink [ 48 ] (Figure 5b–e). Those additives removal requires complicate methodologies and sometimes post‐treatment (i.e., high‐temperature annealing, UV light exposure, and complex washing) procedures that are cost‐effective, inappropriate for scalable manufacturing process and influence on physical/mechanical properties of the printed structure.…”

“…Panels of (c–e) are reproduced with permission. [ 46 ] Copyright 2020, American Association for the Advancement of Science.…”

“…This effect is attributed to non‐uniform solvent evaporation across the droplet during the ink drying procedure, resulting in poor reproductibility performance significant obstacle in scalable manufacturing. [ 13c,46,57 ] Diverse strategies have been investigated to suppress the coffee ring effect. [ 58 ] However, only some of them like Hu et al., [ 46 ] are applicable for 2D crystal inks.…”

“…[ 13c,46,57 ] Diverse strategies have been investigated to suppress the coffee ring effect. [ 58 ] However, only some of them like Hu et al., [ 46 ] are applicable for 2D crystal inks. This may be attributed to some issues such as additives on material functionality, problems of dispersion stability, and postprocessing requirements.…”

“…This may be attributed to some issues such as additives on material functionality, problems of dispersion stability, and postprocessing requirements. [ 46 ] Generally, when an ink droplet is deposited over a substrate, a three‐step solute distribution and alignment in the drop is starting to happen. [ 59 ] The three‐step procedure of solute distribution includes i) recirculation of the solutes by Marangoni flow, ii) nucleation of them at the contact edge, and iii) self‐assembly of the solute by intermolecular forces, respectively (Figure 7b).…”