Physical Supercritical Fluid Deposition: Patterning Solution Processable Materials on Curved and Flexible Surfaces

Abstract

We provide the initial demonstration of a general thin film deposition technique that leverages the unique solubility properties of supercritical fluids. The technique is the solution-phase analogue of physical vapor deposition and allows thin films of a semiconducting polymer to be grown without the need for in situ chemical reactions. Film growth is approximately linear with time, indicating that film thickness can be controlled in a straightforward manner by varying the time of deposition. To further demonstrate the flexibility of the technique, we demonstrate precise control over the location of material deposition using a combination of photolithography and resistive heating. The potential for scalable manufacturing is demonstrated by use of a master to control deposition onto a flexible polymer film. Finally, we demonstrate a unique deposition capability of this technique by depositing patterns onto the curved interior of a hemisphere made from a silicone elastomer. This capability is not possible with any printing or line-of-sight deposition technique. More generally, the ability to control the deposition of solution processed materials with high accuracy provides the long sought after bridge between top-down and bottom-up self-assembly.

Self-assembly of PBTTT–C14 thin films in supercritical fluids

“…Non-monotonic solubility behavior as a function of temperature was observed for both PBTTT-C 14 and isotactic polypropylene in pure n-pentane previously. 32,61 Additionally, the overall absorbance as a function of temperature for different pressures are displayed in Fig. 1 (right panel) using the total integrated intensity obtained from a fit of the data.…”

“…Based on our previous studies, the film thickness increases with respect to time in an approximately linear fashion, which allow us to control film thickness in a relatively straightforward manner. 32 To investigate the morphology of the PBTTT-C 14 films, a series of films were deposited in situ using p-SFD in pure n-pentane and a mixture of n-pentane: toluene (0.5% mol) at different pressures. AFM images shown in Fig.…”

“…We are developing a deposition method for high molecular weight materials that relies on the unique solvation properties of supercritical fluids, called physical supercritical fluid deposition (p-SFD). 32 The technique is designed to maintain the benefits of vapor phase processing and has the additional benefit of not requiring line of sight access to the surface where film formation takes place. When a solvent is at a temperature well below its critical temperature, the saturation concentration of a solid solute typically increases with temperature irrespective of the pressure.…”

“…By controlling the local temperature on a substrate, the deposition process can be directed, achieving linewidths of 5 microns, several times better than aerosol jet printing methods. 32 From an ecofriendly perspective, p-SFD has several benefits. Firstly, the process is highly atom-economical.…”