Flexible CO2 Sensors Based on Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are attractive materials for the construction of printable electronics including thin-film transistors (TFTs) and sensors due to their unique electrical, geometrical and mechanical properties. Here, we describe the synthesis of a novel indigo-fluorene-based copolymer (PFIDBoc) that has been designed to selectively enrich sc-SWCNTs with excellent purity (>99.9%) yet contain a latent function in the form of a tert-butoxy (t-BOC)-protected amine that can be later revealed and exploited for carbon dioxide (CO2) gas sensing. SWCNTs wrapped with the PFIDBoc polymer can be easily converted via an on-chip thermal process to reveal a vinylogous amide moiety with secondary amine nitrogen within the indigo building block of the copolymer which is perfectly suited for CO2 recognition. Thin-film transistors and sensors were inkjet-printed onto rigid and flexible substrates, demonstrating the versatility of enriched PFIDBoc-derived sc- SWCNT dispersions. The printed transistors exhibited a mobility up to 9 cm2 V’1 s’1 and on/off current ratios >105. We further demonstrate herein a CO2 sensor for indoor air quality monitoring even in low humidity environments, possessing a linear response with up to ¼ 5.4% sensitivity and a dynamic range between 400 and 2000 ppm in air with a relative humidity of ¼ 40%.