Large transverse thermopower in shape-engineered tilted leg thermopile

A transverse thermoelectric (TE) device that employs the Nernst effect can generate an electrical potential by applying a temperature gradient perpendicular to the magnetic field. Anomalous Nernst effect (ANE)-based TE materials have been proposed for transverse TE devices due to their advantage of utilizing internal magnetic field of the materials, which offers the benefit of operating without an external magnetic field. To increase the output voltage of transverse TE devices utilizing ANE, materials with higher ANE coefficients, SANE, are required. Currently, SANE reaches ∼6 μV/K at 300 K; however, it is still lower than the Seebeck coefficient of commercial Bi-Te-based TE materials. As proven in conventional TE research, a meticulous design of device structure has the potential to significantly amplify the output voltage for the given material properties. This study proves the same strategy works for transverse TE devices. We demonstrate that a novel device design, where a shape-engineered tilted-leg thermopile structure is employed, significantly enhance the output voltage in the transverse direction. Owing to shape engineering of the leg geometry, an additional temperature gradient develops along the long direction of the leg, which is perpendicular to the direction of the applied temperature gradient, thereby generating an additional Seebeck voltage VSE that adds to the ANE voltage VANE. We further show that a simple adjustment of electrode position within the device can further increase VSE. The tilted leg device with electrode adjustment demonstrates a 990% enhanced transverse output voltage compared to that of conventional rectangular leg thermopile-structured devices, wherein only the ANE occurs. This combined output voltage from both the Seebeck effect and ANE is equivalent to what could be achieved by employing materials with the SANE value of 22.8 μV/K. This value surpasses the SANE of state-of-the-art ANE materials and devices currently available. The numerical analysis shows the tendencies of the electrical and thermal outputs of the tilted-leg device, which guides a way to further improve the output voltage. Our study paves a way to develop highly efficient transverse TE devices that can overcome intrinsic materials challenges by utilizing the degree of freedom of device design.