Measurement and analysis of power conversion efficiency in thin-film and segmented thermoelectric devices

A method for evaluating the power conversion efficiency, and hence ZT_M, of thin-film superlattice, bulk single-stage, and segmented-bulk thermoelectric devices is discussed. The challenge in measuring performance of small-scale devices is the difficulty of explicitly measuring temperatures at TE material junctions. An indirect method, using limited thermocouple measurements and electrical voltage/current measurements, will be detailed in this presentation. A temperature gradient is established across the device, and the resulting open-circuit voltage produced is recorded. In the case of a segmented device, a system of equations and unknowns is formulated and solved numerically, taking into account the variation of bulk material properties with temperature. The results are the temperature gradients across each material leg, allowing for computation of the heat transferred, and thus conversion efficiency. A summary of exceptional results are outlined for a single stage thin-film device and a three-stage cascaded device.