Thin-film thermoelectric generator element characterization

A thermoelectric power generator using thin-film materials presents many challenges due to its inherently large temperature gradient and correspondingly large power density. We present measurements of generated power density from BiTe-based thin-film and thick-film single-element devices (Marlow) in a variety of different element lengths (150-1500 micron) with an experimental setup capable of generating a large temperature difference (>300 K) across the films, and a novel load-matching scheme capable of matching milliohm impedances. Power densities in excess of 2 W/cm have been measured from a single element. The heat spreading in the copper contacts allows an effective heat transfer coefficient of h=18 W/cm²/K, and the parasitic electrical resistance of the system is below 12 mΩ. The same setup has also been used to obtain power measurements on thin-film superlattice thermoelectric elements. The effects of non-idealities such as imperfect impedance matching and non-zero thermal contact resistance are discussed in light of this data.