Novel Measurement Methods for Thermoelectric Power Generator Materials and Devices

Abstract

Thermoelectric measurements are notoriously challenging. In this work, we outline new thermoelectric characterization methods that are experimentally more straightforward and provide much higher accuracy, reducing error by at least a factor of 2. Specifically, three novel measurement methodologies for thermal conductivity are detailed: steadystate isothermal measurements, scanning hot probe, and lock-in transient Harman technique. These three new measurement methodologies are validated using experimental measurement results from standards, as well as candidate materials for thermoelectric power generation. We review thermal conductivity measurement results from new halfHeusler (ZrNiSn-based) materials, as well as commercial (Bi,Sb) 2 (Te,Se) 3 and mature PbTe samples. For devices, we show characterization of commercial (Bi,Sb) 2 (Te,Se) 3 modules, precommercial PbTe/TAGS modules, and new high accuracy numerical device simulation of Skutterudite devices. Measurements are validated by comparison to wellestablished standard reference materials, as well as evaluation of device performance, and comparison to theoretical prediction obtained using measurements of individual properties. The new measurement methodologies presented here provide a new, compelling, simple, and more accurate means of material characterization, providing better agreement with theory.

Determination of thermoelectric properties from micro four-point probe measurements

“…At the final step, all the previously fitted parameters (ϱ, r 2 through r 6 , and b 1 through b 7 ) were fixed, and the filtered, four-point, second harmonic voltage data V 4P,2ω were simultaneously fitted to determine the thermoelectric properties. In the simplified approach which demonstrates the dominant proportionality between V 4P,2ω and α/κ, we neglected the α 2 term in equation ( 5), which enables us to fit the α/κ ratio directly: (10) comparing equation (10) with experimental quantities via:…”

“…To date, the two latter techniques have a narrower in-situ applicability (e.g. imposing constraints on the continuity and layering of the probed materials [10]), while involving a more elaborated experimental setup (e.g. multiple cross-calibrations with reference materials [9]).…”

“…(c) Best-fit contact radii from equation (9). (d) Best-fit α/κ ratio from equation(10); the linear trend in the latter data may be extrapolated to zero current (red lines), retrieving TCR-unaffected intercept which within uncertainties overlaps with the independent estimate α ref /κ ref (see text for discussion).…”

Thin Film Thermoelectric Materials: Classification, Characterization, and Potential for Wearable Applications

“…The heat transfer coefficient of "lock-in transient Harman" method was determined to be about 2%. Its uncertainty was assumed to be closer to 10% [103]. In addition, the thermal conductivity along the cross-plane and in-plane direction have been measured and reported by the 3ω methods and time-domain thermoreflectance measurements (TDTR) [26,55,74].…”