Direct Melt-Calendaring of Highly Textured (Bi,Sb)₂Te₃ Thick Films: Superior Thermoelectric and Mechanical Performance via Strain Engineering

The evolutions of chip thermal management and micro energy harvesting put forward urgent need for micro thermoelectric devices. Nevertheless, low-performance thermoelectric thick films as well as the complicated precision cutting process for hundred-micron thermoelectric legs still remain the bottleneck hindering the advancement of micro thermoelectric devices. In this work, an innovative direct melt-calendaring manufacturing technology is first proposed with specially designed and assembled equipment, that enables direct, rapid, and cost-effective continuous manufacturing of Bi₂Te₃-based films with thickness of hundred microns. Based on the strain engineering with external glass coating confinement and controlled calendaring deformation degree, enhanced thermoelectric performance has been achieved for (Bi,Sb)₂Te₃ thick films with highly textured nanocrystals, which can promote carrier mobility over 182.6 cm² V⁻¹ s⁻¹ and bring out a record-high zT value of 0.96 and 1.16 for n-type and p-type (Bi,Sb)₂Te₃ thick films, respectively. The nanoscale interfaces also further improve the mechanical strength with excellent elastic modules (over 42.0 GPa) and hardness (over 1.7 GPa), even superior to the commercial zone-melting ingots and comparable to the hot-extrusion (Bi,Sb)₂Te₃ alloys. This new fabrication strategy is versatile to a wide range of inorganic thermoelectric thick films, which lays a solid foundation for the development of micro thermoelectric devices.