Performance optimisation of thin film vertical thermoelectric generator

Microfabricated thin film thermoelectric generators can be used for small-scale energy conversion for low power electronics, sensors, or as Peltier coolers with some design adjustment. Most research is in improving the... [ view full abstract ]

Microfabricated thin film thermoelectric generators can be used for small-scale energy conversion for low power electronics, sensors, or as Peltier coolers with some design adjustment. Most research is in improving the material characteristics to improve performance; however, the device design is equally important in ensuring good performance. A lot of research around design optimisation has focused on bulk generators, but microfabricated generators give rise to different design considerations, most notably the usual need for a surrounding medium to provide structural support for the thermoelements. Starting from simplified mathematical models and using FEM simulations it is shown that line-based devices have fewer limitations and have identical performance to conventional square block generators. These studies look at the parasitic thermal and electrical resistances associated with surrounding media and interconnections. A near room temperature device using bismuth and antimony telluride was designed for which the power density and thermal efficiency are assessed. The device was then optimised by changing device pitch, fill factor, thermoelement height, and interconnect conductivity. The findings reveal that, unlike for bulk, the interconnect resistance can be of similar orders of magnitude to the thermoelement resistance, even for good conducting materials, which can reduce performance dramatically. To correct the interconnect resistance the thermoelement height, thermocouple pitch, interconnect material, and the interconnect geometry need to be carefully optimised. Increasing thermal efficiency by changing fill factor depends heavily on the surrounding insulating material and the relative thermal conductance of these materials and the thermoelectric material used.