Highly stretchable and sensitive self-powered sensors based on the N-Type thermoelectric effect of polyurethane/Nax(Ni-ett)n/graphene oxide composites

Abstract

The development of stretchable organic thermoelectric materials is prompted by fast evolving application fields like flexible electronic devices, soft robotics, health monitoring and internet-of-things. Stretchability in thermoelectric materials is usually obtained by using an insulating elastomer, either as a substrate or as a matrix in a blend or composite, which, unfortunately, leads to a compromise in thermoelectric performance. Herein, a potential solution is reported exploiting the addition of graphene oxide as a secondary (nano)filler in a polyurethane/poly nickel-ethenetetrathiolates film. Compared with traditional binary blends, our ternary composite shows an increased electrical conductivity (4 times), air-stability (∼20 times after 3 months), and stretchability (38% increase in strain at break). With a gauge factor (GF) of ∼58, this new composite film shows high sensitivity to tensile strain. Thanks to its Seebeck coefficient of ∼ −40 μV K−1, the composite film can generate a thermopower of ∼0.25 pW when subjected to a small temperature difference (30 °C), which could be exploited by self-powered strain sensors. Therefore, the ternary polyurethane/poly nickel-ethenetetrathiolates/graphene oxide composite film can work as a stretchable strain sensor, providing a strategy to reconcile the compromise between thermoelectric performance and stretchability.