Green Solvent‐Processed Hemi‐Isoindigo Polymers for Stable Temperature Sensors
Jenner H. L. Ngai, John Polena, Daniel Afzal, Xiguang Gao, Mihir Kapadia, Yuning Li
Abstract
Abstract A series of donor‐acceptor polymers, namely PTEB , PMEB , PEEB , and PPEB , are designed and synthesized for temperature sensing. The polymers are composed of hemi‐isoindigo as the acceptor unit, 3,3″‐bis(dodecyloxy)‐2,2″‐bithiophene as the donor unit, and thiophene as the spacer unit. Carbamate solubilizing side chains are used to increase the solubility of the polymers in a green solvent anisole. Furthermore, the carbamate side chains can be thermally removed to form solvent‐resistant polymers PTNB , PMNB , PENB , and PPNB , respectively. The removal of carbamate side chains also helps to elevate the highest occupied molecular orbital energy level of the polymer, thereby promoting p‐doping. PMNB , PENB , and PPNB films are doped with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane ( F4TCNQ ) and used for fabricating temperature sensors on flexible polyethylene terephthalate substrates. The sensors exhibit high temperature coefficient of resistance (TCR) of up to −1.92 (±0.125)% °C −1 at 20–60 °C. This is the highest TCR achieved to date for resistor‐type temperature sensors using a non‐composite single conductive polymer. High sensitivity, green solvent processability, and mechanical flexibility make these temperature sensors promising for use in low‐cost, ubiquitous applications.