Mechanics of the low‐flow limit in slot‐die coating with no vacuum

Abstract

Slot-die coating is a premetered, film-deposition process compatible with a wide range of materials. Of topical interest to precision electronics applications is the deposition of high-cost nanomaterial dispersions over moderately sized (>10 cm 2) areas with submicron wet film thickness. In this work, a two-dimensional (2D) model has been developed to understand the limits of the process and to predict the thinnest possible film achievable. Coined the low-flow limit, this parametric operating boundary presents the minimum uniform, defect-free film achievable at a given set of liquid properties and die/substrate geometry. We investigate the low-flow limit with a model that allows menisci to locate anywhere on the die lands, faces, and substrates with prescribed contact angles, thereby minimizing the assumptions on the bead configuration. The model is validated via comparison of its low-flow limit predictions to published experimental data. Analysis yields insights into the mechanics of coating bead breakdown at the low-flow limit.

Mechanism and Control of the Trailing Edge in Intermittent Slot Die Coating

“…The coating gap H = 161 μm was assumed to be constant because the diameter of the backup roller was much bigger than the computational domain. 16,21 h was the coating thickness.…”

“…θ e was the contact angle between the slurry and the relative static substrate. 21 2.4. Numerical Solution.…”

“…Meanwhile, the upstream length, L up , was set to 2 mm to ensure a sufficient space for the development of the upstream meniscus of the coating bead, and the downstream length, L down , was extended to 5 mm to ensure that the coating layer was fully developed in the downstream direction. The coating gap H = 161 μm was assumed to be constant because the diameter of the backup roller was much bigger than the computational domain. , h was the coating thickness.…”

“…The dynamic contact angle, θ d , was correlated with the Ca value and the equilibrium contact angle, θ e . θ e was the contact angle between the slurry and the relative static substrate …”

Eliminating the Perovskite Solar Cell Manufacturing Bottleneck via High‐Speed Flexography

“…These challenges demand faster, more uniform, and more reliable scalable manufacturing of ultrathin inorganic CTLs to accelerate the commercial viability of planar cell architectures optimized for long-term stability.This work develops a new scalable strategy based on highspeed flexography to meet the technological demand for fabricating ultrathin HTLs in planar inverted perovskite solar cells. Flexography is advantageous for rapid coating of ultrathin wet films of electronic inks without encountering the low-flow limit in slot die coating [20] or the limits of droplet-wise deposition in methods such as spray pyrolysis. [13] This is essential for inorganic hole transport layers (HTLs) that must be characteristically thin (5-50 nm) to achieve high PCE, [21] otherwise requiring expensive vacuum methods such as atomic layer deposition (ALD).…”