A Novel Energy-Efficient Technique to Effectively Decouple Electrical/Thermal Transport of Printable Thermoelectric Composites

Abstract

The rise of wearable electronics has emphasized the need for alternative power sources, as traditional batteries have limitations in terms of portability and cost. One promising solution is thermoelectric power generation, which involves harnessing body heat to power these devices using thermoelectric (TE) materials. However, most TE materials are costly, often toxic, and not practical for mass production. In this study, we focused on tetrahedrites, a class of TE materials made from non-toxic, abundant, and low-cost elements. Our goal was to separate the electrical and thermal conductivity in tetrahedrite composite TE films, and we developed an innovative and energy-efficient film fabrication method to achieve this. We initially applied this method to well-known TE materials, p-type Bi0.5Sb1.5Te3 (BST), and n-type Bi2Te2.7Se0.3 (BTS). Using cost-effective screen printing, we successfully created thick p-type Chitosan-BST thermoelectric composite films with a remarkable maximum ZT of 0.7 at room temperature (RT). We also designed a 3-leg thermoelectric generator (TEG) device that produced 58 ?W of power and a power density of 5.72 mW/cm2 at a 38 K temperature difference. Employing the same technique, we produced thick n-type Chitosan-BTS composite films, achieving a maximum ZT of 0.4 at RT. Additionally, we constructed a 2-leg TEG device, generating 0.48 ?W at a 12 K temperature difference. Our research also explored the impact of our energy-efficient film fabrication on composite Tetrahedrite films. We successfully produced thick p-type Chitosan-based TE films using three different Tetrahedrite compounds: Cu12Sb4S13, Cu10Ni2Sb4S13, and Cu10Ni1.5Zn0.5Sb4S13, via cost-effective screen printing. Notably, the Chitosan-Cu12Sb4S13 TE composite film achieved a high power factor of 96 ?W/mK2 at RT, with the lowest thermal conductivity recorded at 0.71 W/m-K. This resulted in a ZT value of 0.04 at RT. Furthermore, we examined the potential of incorporating a small quantity of MXene into Tetrahedrite materials, anticipating improved electrical conductivity. The results were significant. A thick Chitosan-Cu12Sb4S13 TE composite film, combined with 2-D MXene nanosheets, showed a threefold increase in the power factor (302 ?W/mK2) and nearly 30% reduction in thermal conductivity (0.51 W/m-K). This led to a 4.5-fold improvement in ZT, reaching 0.18 at RT. In conclusion, we've managed to decouple the different parameters affecting thermoelectric performance. Simultaneously, we've created thermoelectric films and devices that are efficient, eco-friendly, and easy to produce, and they work well in situations with minimal wasted heat. These results suggest that printed TEGs could be a reliable energy source for wearable devices, especially those used for continuous monitoring.