PAD-Flex-TEG: Nanocrystalline μm-dicke Bismuttellurid-Schichten für flexible µm-thick bismuth telluride films cold-deposited directly from powder for flexible thermoelectric generators

• Applicants: Dr.-Ing. Jaroslaw Kita; Dr.-Ing. Daniela Schönauer-Kamin
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544448150

PAD-Flex-TEG combines the high thermoelectric performance of bismuth tellurides at room temperature with powder aerosol deposition (PAD) method to generate nanocrystalline functional layers of low thermal conductivity on bendable substrates for high-efficiency flexible thermoelectric generators (Flex-TEG). Through comprehensive thermoelectric characterization of n- and p-type PAD bismuth telluride films, their performance capabilities are evaluated against the background of nanocrystalline morphology, mechanical distortions, and anisotropic film properties, and favoring factors are identified. With its manifold tasks for material preparation as well as characterization, the research project combines the scientific competences of both applicants. Specifically, the potential but also the limitations of PAD functional layers for flex-TEGs are to be elaborated based on the thermoelectric characteristics of three differently doped bismuth tellurides. In addition to polymer films, ultrathin inorganic films of yttria-stabilized zirconia (YSZ) of different thicknesses are applied as flexible substrates. In PAD, dense nanocrystalline layers with atomic lattice deformations are formed by the impact of ceramic particles. It is necessary to work out how the process parameters as well as the mechanical properties of the flexible substrates influence the microstructures of the PAD bismuth telluride films and their thermoelectric characteristics. Moderate thermal post-treatment could increase the charge carrier mobility of the nanocrystalline microstructure by relaxation of micro-stresses, but without promoting inhibited heat conduction by crystallite growth. Regarding an application of PAD for flex-TEGs, it is to be investigated how permanent and alternating mechanical loads in the longitudinal direction of the PAD layers affect the thermoelectric performance during and after deformation and which maximum bending radii are possible depending on the layer thicknesses. In addition, it should be investigated whether anisotropic macro-stresses introduced selectively during film preparation can improve the functional properties of mechanically loaded thermoelectric films. Finally, a first proof of function as a flexible planar dual-leg TEG with contacted n- and p-conducting PAD layers on a flexible carrier is to be provided. It will be evaluated to which extent the thermoelectric performance of the PAD-induced nanocrystalline microstructure exceeds those of conventionally process thick and thin film TEGS. The project results could be the starting point for further research on the potential of innovative PAD functional layers in flex-TEGs, which should also be of industrial interest thanks to the scalability of PAD.

• DFG Programme: Research Grants