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.

The rapid growth of wearable electronics, Internet of Things, smart packaging, and advanced healthcare technologies demand a large number of flexible, thin, lightweight, and ultralow-cost sensors. The accurate and precise determination of temperature in a narrow range (~0–50 °C) around ambient temperatures and near-body temperatures is critical for most of these applications. Temperature sensors based on organic field-effect transistors (OFETs) have the advantages of low manufacturing cost, excellent mechanical flexibility, easy integration with other devices, low cross-sensitivity, and multi-stimuli detectability and, therefore, are very suitable for the above applications. This article provides a timely overview of research progress in the development of OFET-based temperature sensors. First, the working mechanism of OFETs, the fundamental theories of charge transport in organic semiconductors, and common types of OFET temperature sensors based on the sensing element are briefly introduced. Next, notable advances in the development of OFET temperature sensors using small-molecule and polymer semiconductors are discussed separately. Finally, the progress of OFET temperature sensors is summarized, and the challenges associated with OFET temperature sensors and the perspectives of research directions in this field are presented.

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