Thermoelectric properties enhancement of p-type composite films using wood-based binder and mechanical pressing

Thermoelectric generators (TEGs) fabricated using additive manufacturing methods are attractive because they offer the advantages of scalability, lower cost, and potentially higher power density than conventional TEGs. Additive manufacturing of TEGs requires active thermoelectric particles to be dispersed in a polymer binder to synthesize printable slurries, and printed films to be subsequently subjected to a long and high temperature curing to enhance their thermoelectic properties. A large amount of polymer binder present in composite films results in a sizable loss in the electrical conductivity. In addition, a long and high-temperature film curing results is a slow and energy intensive fabrication process. In this work, we demonstrate the feasibility of using a small amount (≤10^-3 wt ratio) of novel nanofiber cellulose (NFC) as a binder to provide sufficient adhesion strength to hold the TE particles together in the composite films. We also demonstrate a pressure induced densification process to enhance the thermoelectic properties of printed composite films. This novel approach has the potential to fundamentally transform the manufacting method for printing TEGs by eliminating the need of long-duration and high-temperature curing. A higher applied pressure leads to a compact packing and densification of films resulting in an improvement in the electrical conductivity. The highest power factor achieved for best performing p-type thermoelectric-NFC composite film subjected to pressure induced densification is 611 μW/m-K².