Screen-printed, flexible, and eco-friendly thermoelectric touch sensors based on ethyl cellulose and graphite flakes inks

Abstract

Despite the undoubtable interest in energy conversion, thermoelectric materials can be approached from a temperature-sensitive perspective, as they can detect small thermal stimuli, such as a human touch or contact with cold/hot objects. This feature offers possibilities for different applications being one of them the integration with scalable and cost-effective, biocompatible, flexible, and lightweight thermal sensing solutions, exploring the combination of sustainable Seebeck coefficient-holding materials with printing techniques and flexible substrates.
In this work, ethyl cellulose and graphite flakes inks were optimized to be used as functional material for flexible thermal touch sensors produced by screen-printing. Graphite concentrations of 10, 20 and 30 wt% were tested, with 1, 2 and 3 printed layers on four different substrates - office paper, sticker label paper, standard cotton, and organic cotton. The conjugation of these variables was assessed in terms of printability, sheet resistance and thermoelectric response. The best electrical-thermoelectric output combination is achieved by printing 2 layers of the ink with 20 wt% of graphite on office paper substrate. Subsequently, thermal touch sensors with up to 48 thermoelectric elements were produced to increase the output voltage response (> 4.5 mV) promoted by a gloved finger touch. Fast and repeatable touch recognition was obtained in optimized devices with a signal-to-noise ratio up to 340 and rise times bellow 0.5 s. The results evidence that the screen-printed graphite-based inks are highly suitable for flexible thermoelectric sensing applications.

Fabrication of low-cost flexible thermoelectric generator using conductive HB graphite paint operated by solar radiation

“…Hence, our main focus is on the inks prepared from carbon and its derivatives, as these inks offer significant benefits over inorganic heavy metals in terms of their solution process ability, abundant nature and low cost of production. In 2018, Juntunen et al [10] prepared largearea flexible graphene-silver based thin film device on polyethylene terephthalate (PET) via inkjet-printer and produced an output voltage of 10 mV at temperature difference of 10 K. Recently in 2023, Figueira et al [11] designed thermal touch sensors by screen printing using ethyl cellulose and graphite flakes inks on an office paper substrate and obtained output voltage response of greater than 4.5 mV in 48 TE elements, by producing ∆T with just one finger touch along the samples.…”