Chitosan-Based Electronics: The Importance of Acid Strength and Plasticizing Additives on Device Performance

A rise in demand for disposable consumer electronics such as smart packaging, wearable electronics, and single-use point-of-source sensors requires the development of eco-friendly and compostable electronic materials. Chitosan is derived from crustacean waste and offers high dielectric constant values without requiring rigorous purification, making it sustainable for large-scale electronic device manufacturing. When processed in acidic media, the protonated backbone of chitosan pairs with counterions from the acid dissociation to form chitosan thin films with electrical double layers (EDLs) and tunable capacitive properties. We report the importance of the choice of acid when processing chitosan by surveying a series of halogenated and biosourced acids with varying pK_a values and solutions with different pH values. Oxalic acid outperforms other acids, with a maximum areal capacitance of 161 nF·mm^-2. Tartaric acid and citric acid, despite lower capacitance values, showed promising results with a stable EDL capacitance and high reproducibility, making them optimal for large-area manufacturing. The incorporation of sorbitol as a plasticizer boosts the EDL formation onset of all chitosan-acid combinations to 1 × 10³-10⁵ Hz and improves reproducibility. High-performing single-walled carbon nanotube thin film transistors were made using chitosan-based dielectrics treated with different acids with and without sorbitol, leading to transconductance as high as ≈5.2 μS and I_on/I_off of 10⁵. The capacitors and transistors remain functional after one year of storage in ambient conditions. Overall, this study demonstrates durable high-performance electronics based on chitosan and stresses the importance of processing acid and the use of plasticizing additives, such as sorbitol.