2D printable flexible based n-type bulk thermoelectric materials and printable flexible high power density TEG
Environmentally stable, 2D/3D printable inorganic thermoelectric materials on an Ag-Se n-type basis with high thermoelectric (TE) performance. The corresponding flexible thermoelectric generators (TEGs) can be manufactured reproducibly and efficiently with a cost-effective printing process, show high power density and allow wider applications i.e. they can be integrated into non-flat surfaces of different micro and complex electronic or mechanical systems.
Thermoelectric generators (TEGs) convert heat flux (temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect. This promising energy conversion technology is less bulky and uses no moving parts compared to conventional heat engines. Unfortunately, TEGs are typically more expensive, less efficient and not in a position to compete with other environmentally friendly energy conversion technologies like photovoltaics. Therefore, TEGs are not yet used to a large extent for real-life applications. Only widely known Bi-Te based materials are successfully implemented for TE device applications at ambient temperature. Production of low cost and high outputpower density TE devices using conventional bulk materials is unsatisfactory due to a large amount of material used and complex manufacturing processes. In addition, TEGs made of bulk materials are usually not flexible and hardly integratable into non-flat surfaces of different micro and complex electronic or mechanical systems. One the other hand, conductive polymers might be potential candidates for flexible TE materials due to their good printability, environmental stability, high electrical conductivity and low thermal conductivity. However, they exhibit low TE performance. Nevertheless, efforts are still being made to enhance TE performance of conductive polymers, such as p-type PEDOT and n-type 1,1 ,2,2-ethenetetrathiolate(ett)-metal coordination polymers [poly[Ax(M-ett)] through hybridization and functionalization with different inorganic or organic elements and compounds.
Even though some organic-based printable p-type TE materials have been reported, there are currently no known sufficiently efficient and environmentally stable printable n-type TE materials for device manufacturingTEGs made of bulk materials are usually not flexible. If they are printed nevertheless, bulk materials, binders, solvents and additives strongly interfere with the TE transport parameters at grain boundaries, especially the electrical conductivity, resulting in poor TE performance. In summary one can say that state-of-the-art TE materials have either low Seebeck coefficients, poor printability and/or environmental instability.
An innovative strategy for producing printable flexible Ag-Se-based n-type thermoelectric materials comprising a binary Ag2Se phase, which is based on a moderate temperature post printing sintering procedure to avoid detrimental effects at grain boundaries preserving its high TE performance. Unlike conventional inorganic powder based printed films containing grain boundaries, interruption of carrier transportation through the percolated path of the Ag2Se phase is minimized, which results in high advantageaus electrical conductivity, and thus in a very good TE performance.In addition, this n-type thermoelectric material can be combined with our recently developed corresponding p-type material based on Cu2Se (see our ref. 21/010TLB) for even more powerful TEG.
Fields of application
Printable, flexible thermoelectric (TE) materials particularly for large scale applications. Integratable into non-flat surfaces of different micro and complex electronic or mechanical systems.