Exploring Form and Functionalization in Crystalline Nanocellulose Inks for Environmentally Sustainable Printed Electronics

Printed flexible electronics show promise for providing a sustainable solution to the increasingly negative impact of electronics manufacturing and waste. However, current print processes and inks tend to rely on hazardous solvents, extensive post-processing at high temperatures, and/or materials that are not recyclable or biodegradable. Recent work on water-based inks from nanomaterials shows that these challenges can be overcome (i.e., no hazardous chemicals, relatively low temperature processing, and all recyclable or biodegradable materials), but the resultant devices still require improvement in performance and reproducibility. In this work, we investigated two new water-based inks for use in carbon nanotube (CNT) thin-film transistors (TFTs): nanocellulose, a biodegradable ionic dielectric, and nanoparticle gold, a recyclable conductor. We developed inks and aerosol jet printing processes for crystalline nanocellulose (CNC) and cellulose nanofibrils (CNF) with various surface groups to gain insights into the working mechanisms of nanocellulose as an ionic dielectric. Our results reveal that the general ionic nature of the printed films is invariant with the nanostructure form or surface group. However, the capacitance and sweep rate characteristics of the dielectrics, as well as the electrical and mechanical resilience, do show dependencies on nanocellulose form and functionalization. Further, we investigated the influence of the sulfonic surface group content on transistor performance, revealing that the foremost impact of increasing the sulfonation is a positive shift in the device threshold voltage. Since nanocellulose breaks down under high temperatures, the top-gate contact must be readily conductive when printed to form fully printed CNT-TFTs. Therefore, as an alternative to using graphene, a novel gold ink formulation was used as the contacts for CNT-TFTs. This new ink exhibited a resistance of ~5 Ω in its as-printed state, without any post-print sintering at high temperatures. The impressive device performance of these printed CNT-TFTs shows promise for the use of water-based inks in environmentally sustainable printing of electronics.