This review provides a general overview on the recent advances for organic-based thermoelectrics with an emphasis on the most thoroughly investigated material classes and the approaches employed to control their thermoelectric transport properties.

The thermoelectric properties of Co-Sb thin films with different Sb content and with a thickness of 30 nm were investigated with respect to the composition and the corresponding structural properties of these films. The films were prepared by molecular beam deposition either by codeposition on heated substrates or room temperature deposition followed by a post-annealing step. It was found that the prepared films exhibit bipolar conduction, indicated by a positive Hall constant and a negative Seebeck coefficient. The obtained results can be well explained by using the bipolar model, assuming heavy electrons and light holes, which was finally confirmed experimentally by the preparation of p-and n-type doped CoSb 3 thin films. Furthermore, variable range hopping was identified by temperature dependent transport measurements as dominant conduction mechanism at low temperatures.

While the process of metal induced crystallization (MIC) is widely used in the fabrication of thin film electronic devices, its application to the field of thermoelectrics is fairly new. Especially its implementation in the field of the classic thermoelectric material SiGe could lead to a low cost approach by combining the benefits of low thermal budget, self-doping, and thin film and sputter deposition compatibility. In this work, samples consisting of SiGe/Al multilayers deposited on aluminum oxide based substrates have been prepared. Special emphasis was put on the ratio of Al to SiGe and the resulting changes in transport properties during annealing. On the one hand a certain amount of Al is needed to ensure a complete MIC process for the SiGe, but on the other hand an excess of Al results in a metallic system with low thermoelectric efficiency. In-situ characterization during annealing of the samples was carried out via x-ray diffraction, electrical resistivity, and Seebeck measurements.

The effect of metal induced crystallization (MIC) is widely used in the production of electronic devices by forming large grained polycrystalline Si from amorphous Si in contact with Al. This effect can also be utilized in conjunction with silicon-germanium (SiGe) alloys and thus provides means of a possible low cost production of future high temperature thermoelectric devices. In this work, sputter deposited multilayer systems of Si 80 Ge 20 /Al thin films have been investigated. The effect of MIC is used to crystallize the initially amorphous SiGe while simultaneously doping it with Al. As metallic phases would be detrimental to the thermoelectric performance, special interest is directed to the Al layers and their dissociation during the annealing treatment. A percolation limit regarding the thickness and continuity of the Al layers was found, but no detrimental side effects with respect to the MIC process could be detected.

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