Solvent-Mediated Diffusion Enables Directed Functionalization of Polymer Semiconductor Interfaces

The increasing interest in the development of intrinsically stretchable electronic devices based on polymer semiconductors (PSCs) necessitates a comprehensive understanding of the interfacial chemistry of these PSC films, alongside facile processing methods to modify these properties, which dictate layer compatibility. Solvent-mediated functionalization provides a scalable, controllable, and tunable method to target and modulate several key interfacial properties. Herein, we aim to understand the influence of solvent exposure on a blended polymer film. This is achieved through small molecule modification of a poly-thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTT) and low molecular weight polybutadiene (BA)-blended elastomer film. We investigated solvent-mediated film functionalization on blended films by incorporating 1H,1H,2H,2H-perfluorodecanethiol (PFDT), as the highly fluorinated small molecule provided excellent measurement contrast throughout several characterization techniques. By comparing solvent environments that differentially swell the blended polymer films, we show programming of PFDT incorporation from uniform, through-thickness functionalization to surface-enriched gradients. Quartz crystal microbalance with dissipation monitoring (QCM-D) measurements and further corroborated with X-ray photoelectron spectroscopy (XPS) depth profiles quantified the estimated apparent mass uptake of PFDT. In a non-swelling/compacting solvent environment, QCM-D reflected a diffusion-governed uptake of PFDT with a distinct thickness-dependent concentration gradient. In contrast, swelling films with methoxyperfluorobutane (MPFB) opened diffusion pathways that facilitated PFDT penetration throughout the entire polymer network and resulted in more uniform functionalization across the entire film thickness. Collectively, these results establish a broader understanding of solvent-mediated film functionalization and further the understanding of molecular diffusion through PSC film systems.