Leg geometry and contact resistance cap what a thermoelectric generator actually delivers
A thermoelectric generator turns a temperature difference into electricity, and the field has long chased better materials to raise its output. A new thermodynamic model reaches a different conclusion: inside a working module the ceiling is set by the shape of the conversion legs and by the electrical resistance where those legs meet their metal contacts. Reworking that geometry and those interfaces buys more efficiency than another step in the material figure of merit.
Science··Evening
The ceiling sits in the module, not only in the material
A thermoelectric generator produces current directly from a temperature difference across small blocks of semiconductor called legs. Research effort has concentrated on the figure of merit, the single number that ranks how well a material performs that conversion. A comprehensive thermodynamic model now finds that the output of a real generator is bounded first by the aspect ratio of those legs, the relation between their length and their cross-section, and by the contact resistance at the interfaces where current enters and leaves them.[1]
Scaling laws for heat that leaks and current that stalls
The work derives analytical scaling laws, compact expressions that show how a quantity grows or shrinks with device dimensions, across different module architectures. Three losses enter them together: thermal bypass, the heat that travels around the legs instead of through them; the electrical impedance of the contacts; and the coupling between the module and the heat exchangers that hold its hot and cold sides apart. Written this way, the relations apply to a family of designs rather than to one tested device.[1]
Where the next efficiency gain is cheaper to find
The design consequence is concrete. Shaping the legs and improving the metallization interfaces, the metal layers bonded to each leg to carry current out, yields a larger efficiency gain than an incremental improvement in the material figure of merit. That reorders a research priority that had put the search for a better material first, and it moves the next efficiency gain into the engineering of the module itself.[1]
