Heat Conduction in a Printed Thermoelectric Film

We have developed printed thermoelectric thin films using inorganic materials such as Bismuth Telluride. The process involved crushing the material into fine powders and mixing it with polyamic acid in an organic solvent. The resulting viscous solution was screen-printed onto a substrate and annealed in an Argon atmosphere. The heated polyamic acid transformed into polyamide at 400°C, acting as an adhesive between the thermoelectric powders. However, we found that the electrical conductivity of the resulting film was very low due to the low packing density. To address this issue, we decided to create a composite material by incorporating printable materials. We chose the lead-free halide perovskite, CsSnI₃, which displayed relatively good thermoelectric properties as a printable material. We mixed the Halide perovskite into the Bismuth Telluride solutions and printed them onto the substrate. After heating the film on a hotplate, the halide perovskite precipitated in the pores, resulting in a composite film of Bi₂Te₃/CsSnI₃. This composite film displayed improved electrical conductivity and low thermal conductivity, while the Seebeck coefficient slightly decreased. We also found that the thermal conductivities of both Bismuth telluride and Halide perovskite were low, and the high interfacial thermal resistance between them was measured to be in the order of 10^-7K/(m²●W) using the differential 3omega method. This high interfacial thermal resistance explained the low thermal conductivity of the composite film, following a conventional model with interfacial thermal resistance. Ab initio calculations helped us understand the mechanisms behind the high interfacial thermal resistance. We believe that our printing process can be applied to other thermoelectric materials, allowing us to create film-shaped thermoelectric generators. Then, we applied the present printing technique to Cobalt antimonide Skutterudite. The Cobalt antimonide shows a high power factor at room temperature although thermal conductivity is also high. The effective thermal conductivity of the printed film is low, as well as keeping a relatively high power factor at room temperature. The packing density should be increased to improve the electrical conductivity of the printed Cobalt antimonide Skutterudite. This method can be applied to make thermoelectric energy harvester for room temperature use.