High-Performance Thermoelectric Flexible Ag₂Se-Based Films with Wave-Shaped Buckling via a Thermal Diffusion Method

Herein, an n-type Ag 2 Se thermoelectric flexible thin film has been fabricated on a polyimide (PI) substrate via a novel thermal diffusion method, and the thermoelectric performance is well-optimized by adjusting the pressure and temperature of thermal diffusion. All of the Ag 2 Se films are beneficial to grow (013) preferred orientations, which is conducive to performing a high Seebeck coefficient. By increasing the thermal diffusion temperature, the electrical conductivity can be rationally regulated while maintaining the independence of the Seebeck coefficient, which is mainly attributed to the increased electric mobility. As a result, the fabricated Ag 2 Se thin film achieves a high power factor of 18.25 μW cm –1 K –2 at room temperature and a maximum value of 21.7 μW cm –1 K –2 at 393 K. Additionally, the thermal diffusion method has resulted in a wave-shaped buckling, which is further verified as a promising structure to realize a larger temperature difference by the simulation results of finite element analysis (FEA). Additionally, this unique surface morphology of the Ag 2 Se thin film also exhibits outstanding mechanical properties, for which the elasticity modulus is only 0.42 GPa. Finally, a flexible round-shaped module assembled with Sb 2 Te 3 has demonstrated an output power of 166 nW at a temperature difference of 50 K. This work not only introduces a new method of preparing Ag 2 Se thin films but also offers a convincing strategy of optimizing the microstructure to enhance low-grade heat utilization efficiency.