Optimization of Carbohydrate-Bearing Semiconducting Polymers: A Case Study toward Greener High-Performance Electronics

Semiconducting polymers are vital to the development of next-generation electronics due to their excellent physical and optoelectronic properties. These materials possess several advantages over current silicon-based electronics, including good mechanical features, synthetic tunability, and the potential for emerging properties such as self-healing and biocompatibility. Another major advantage of semiconducting polymers is their solution processability, which allows manufacturers to access a wide variety of new fabrication techniques such as spin-coating and inkjet printing to produce thin-film electronics. While solution processing offers many new avenues for electronics production, it also leads to a major ecological concern. Due to the extended π-conjugation of these materials, their solubility is often limited to toxic, halogenated solvents that can be extremely harmful to humans and the environment. As such, the significant environmental toll of processing these materials at an industrial scale needs to be proactively considered.<br/>In recent years, several strategies have been proposed to avoid the use of such toxic solvents, either by careful selection of new solvent systems or engineering of polymer structures to alter their solubility. Using a molecular engineering approach, we developed alcohol-processable semiconducting polymers using carbohydrate side chains. These pendant groups were chosen because they are bio-sourced, non-toxic and contain many alcohol groups. The use of carbohydrates to improve solubility has been extensively used in the medical industry, but has not previously been applied to electronic materials. The extensive hydrogen bonding of these new side chains significantly improved solubility of the semiconducting polymer in more polar solvents, including n-butanol. The use of carbohydrate moieties was also found to have little impact on electronic performance in organic field-effect transistors (OFETs), making this a viable approach toward greener electronics fabrication without sacrificing performance. Interestingly, these new side chains were found to have significant impacts on thin film morphology and solid-state stacking when incorporated into the polymer in different ratios. Since morphology and packing can directly affect charge mobility, the use of these carbohydrate side chains has been systematically investigated in semiconducting polymers as not only an avenue toward eco-friendly device manufacturing, but also a novel way to improve charge transport for high-performance OFETs. This work presents an in-depth case study of the effects of polymer structure and processing conditions on electronic performance. This foundational study demonstrates that novel side chain engineering is key to the future of environmentally conscious next-generation electronics.