2D printable inorganic n-type thermoelectric materials for printable flexible high power density TEG
Scientists at the Karlsruhe Institute of Technology (KIT) have developed environmentally stable and 2D printable inorganic thermoelectric materials on an Ag-Se n-type basis with high thermoelectric (TE) performance. The corresponding flexible thermoelectric generators (TEGs) based on these innovative materials can be manufactured efficiently with a cost-effective printing process. These TEGs 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 output power 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. On 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 manufacturing. TEGs 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 or environmental instability.
Now an innovative strategy for producing printable flexible Ag-Se-based n-type thermoelectric materials comprising a binary Ag2Se phase was devoloped. It 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.
- Novel Ag-Se based n-type thermoelectric (TE) materials,
- 2D printable,
- environmentally stable,
- high power density and high TE performance,
- moderate temperature post-printing sintering procedure,
- low-cost manufacturing of high power density 2D printable flexible TEG.
Printable, flexible thermoelectric (TE) materials particularly for large scale applications. Integratable into non-flat surfaces of different micro and complex electronic or mechanical systems. They, thereby, present a versatile and maintenance-free solution for low-temperature energy-harvesting applications ranging from wearable electronics over energy self-sufficient sensors for the Internet of Things and Industry 4.0 to large-scale waste heat recovery.