Inkjet printing as a flexible technology for the deposition of thermoelectric composite structures

In this work we demonstrate that thin-film thermoelectric composite structures can be easily fabricated using inkjet technology. A major advantage of this procedure is the formation of tailored composite structures from the precursor inks using a provided pattern. Depending on the structural design, the thermoelectric properties of fully Inkjet-printed single-element thermoelectric generators (TEGs) show thermoelectricity in the 10 mV range and currents in the mA range. The study represents the basic phenomena of thermoelectric composite structures despite from the magnitude of thermoelectric properties of the composite components. The precursor inks we use are poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate)-ink (PEDOT:PSS-ink),ZnO-ink and Ag-ink for the interconnects. PEDOT:PSS is a conductive polymer and forms the matrix of the composite containing different amounts of ZnO-nanoparticles. We observed nearly a doubling of the thermoelectric voltage and constant current in comparison of a PEDOT:PSS/ZnO-composite with pure PEDOT:PSS, except the two times higher resistance of acomposite-based TEG. Increasing the amount of ZnO-nanoparticles leads to higher voltage but a deterioration of the resistance is also observed. With increasing values of ZnO-nanoparticles in the polymer PEDOT:PSS and ZnO-nanoparticles form strong minted separate areas like "vesicles" type with a boundary layer containing the composite. This results in a lower thermoelectrical performance because of a resulting high resistance of the TEG. Furthermore, possibilities of reducing the resistance of the composite structures could be realized by adding metal nanoparticles or simply by varying the printing process of the precursor inks.