Spray-coated PEDOT:OTf films: thermoelectric properties and integration into a printed thermoelectric generator

Organic conducting polymers are promising materials for thermoelectric applications due to their high electrical conductivity and intrinsic low thermal conductivity. Among them, poly(3,4-ethylenedioxythiophene) (PEDOT) has a positive Seebeck coefficient (p-type) and is commercially available. It has therefore gained a lot of attention in the field. However, it remains challenging to process a large amount of organic thermocouples to produce an efficient thermoelectric generator (TEG). In addition, finding a way to use bidimensional (2D) printed thermocouples in a tridimensional (3D) TEG structure is not straightforward. In this article, we propose the use of ultrasonic spray-coating as a straightforward large-scale printing technique to prepare highly conducting and in-situ polymerized PEDOT:OTf. The spray-coated material can reach an electrical conductivity as high as 2215±665 S.cm-1 at 132±10 nm film thickness. We studied the influence of several parameters, such as co-solvent addition, thickness control and rinsing procedure on the conduction properties. GIWAXS and low temperature electrical conductivity measurements on films of different thicknesses allowed us to elucidate the structures of the as-prepared materials and the charge transport mechanisms. Finally, a fully printed and rolled TEG containing 156 thermocouples was prepared as a proof of concept, generating a power output of 1 µW with a 48°C thermal gradient.