3D-Printed Geometrical-Optimized Bridge-Type Thermoelectric Generators with a High Output Power and Mechanical Robustness.

The geometric design of thermoelectric (TE) devices plays a key role in their performance, especially in terms of their energy conversion efficiency and mechanical robustness. In this study, we employed the shape-customization capabilities of three-dimensional (3D) printing to develop a novel bridge-type thermoelectric device with an enhanced device performance. To fabricate the TE devices, p-type and n-type Bi2Te3-based TE materials were prepared through Selective Laser Melting (SLM), characterized by the pronounced anisotropy due to rapid cooling and steep temperature gradients during printing. Consequently, the highest ZT values for 3D printed p-type Bi0.5Sb1.5Te3 (BST) and n-type Bi2Te2.7Se0.3 (BTS) were 1.12 and 1.02, respectively, as the material basis for the subsequent device fabrication. Then, attributed to the design freedom of 3D printing technology, particularly in customizable shapes and rapid prototyping, this study proposed a bridge-type structure for TE devices. Comparative studies on electrical and mechanical properties between bridge-type structures and traditional π-type TE devices are conducted. It was found that the bridge-type design demonstrated a superior electrical performance with an optimized current density and reduced internal resistance, achieving a theoretical output power of 0.168 W and conversion efficiency of 5.4%, with the corresponding improvements of 18 and 11%, respectively. In addition, compared to the traditional structure susceptible to excessive stress, our bridge-type structure directly connects each TE leg, thereby effectively mitigating the stress concentration induced by mismatched thermal expansion coefficients among components. As a result, the maximum thermal stress of the TE module is reduced to 89.9 MPa, just 82.5% of the 109.0 MPa observed in traditional structures. This study highlights the significance of performing geometric design through the 3D printing technique to develop high-performance mechanically durable thermoelectric systems for energy-harvesting applications.