Interfacial Engineering to Decouple Electrical and Thermal Conductivities in an Energy Efficient Low Thermal Budget Additive Manufacturing Technique for Flexible Thermoelectric Generators

The global focus on renewable and consistently available energy sources has given rise to research into alternative sources of energy harvesting, such as thermoelectric generators (TEG). TEG devices provide the solid-state conversion of waste heat into electrical power by utilizing the Seebeck effect. Thermoelectric (TE) performances can be measured by a dimensionless figure of merit (ZT). To increase the ZT value of a TE material, it is necessary to increase both the electric conductivity (EC) and Seebeck coefficient (SC) while minimizing the total thermal conductivity (TC) of the material. These values are highly interdependent and difficult to independently control. The scalability of traditional thermoelectric generators (TEGs) has been held back by the inclusion of a high-temperature, long-duration curing process to produce high-performance thermoelectric (TE) films. Additive manufacturing has been investigated as a more time, energy, and cost-efficient method compared to traditional manufacturing techniques. Importantly, additive manufacturing allows for design freedoms including the addition of flexibility in the fabrication of TEGs. With a growing interest in the widespread adoption of TEGs to capture low waste heat energy from non-planar surfaces like the human body, the need for flexible, high performance, and energy-efficient TE manufacturing techniques is increasing. This work investigates the synergistic effect of a small amount of chitosan binder (0.05wt%), a micron and nanosized particle size distribution, the application of mechanical pressure (20 MPa), thickness variation (170µm vs 300µm) – on the performance of p-Bi 0.5 Sb 1.5 Te 3 (p-BST) and n-Bi 2 Te 2.7 Se 0.3 (n-BTS) TE composite films manufactured using a low thermal budget manufacturing technique. The combination of these four factors controls the micro and nanostructure of the films to decouple their electrical and thermal conductivity effectively. This resulted in figures of merit (ZTs) of 0.89 and 0.5 for p-BST and n-BTS, respectively - comparable to other additive manufacturing methods despite eliminating the high-temperature, long-duration curing process. The process was also used to fabricate a 6-couple f -TEG device which could generate 357.6 µW with a power density of 5.0 mW/cm 2 at a ∆T of 40 K. The device demonstrated air stability and flexibility for 1000 cycles of bending. Finally, the device was integrated with a voltage step-up converter to power a LED and charge and