Standard Reference Thermoelectric Modules Based on Metallic Combinations and Geometric Design

To establish a reliable thermoelectric module evaluation, a Standard Reference Thermoelectric Module (SRTEM) was developed based on stability. Open-circuit voltage (Voc) was selected as the key calibration parameter due to its consistent response to temperature differences (ΔT). The SRTEM consists of eight p–n thermoelectric couples composed of metallic thermoelectric materials—Ni90Cr10 (chromel), Cu55Ni45 (constantan), Fe64Ni36 (invar), and pure Fe—selected based on their thermoelectric properties, structural compatibility, and contact resistance. Among the tested combinations, the chromel–constantan pair exhibited the highest Voc of 55 mV at ΔT = 150 K. To increase Voc and expand the usable calibration range, leg-shape modification and substrate replacement were investigated. Module simulation revealed that replacing the rectangular-leg geometry with a double-hourglass (2H/G) structure could increase Voc by 20.2%. Furthermore, measurement of single-leg modules with substrates attached confirmed a 16.0% improvement in Voc for the 2H/G shape over the rectangular shape, consistent with the predicted enhancement due to increased thermal resistance. In addition, replacing the alumina substrate with a higher thermal conductivity material, such as AlN, increased ΔT across the legs and yielded a further 9.1% improvement in Voc. These results demonstrate the potential of the proposed SRTEM as a calibration standard for consistent thermoelectric module measurements.