Annealing-induced transformation of structural and optical parameters of transparent γ-CuI thin films with superior thermoelectric performance

The synthesis of transparent thermoelectric materials, particularly at low processing temperature possesses a good promise for future power generation by renovating waste heat into electrical energy. The fabrication of invisible thermoelectric module is hindered by limited choices of appropriate p-type transparent thermoelectric materials so far. The present study deals with the growth and characterization of optically transparent p-type copper iodide (γ-CuI) thin films. Thermal annealing (maximum up to 200 °C) was performed to tune the electrical and optoelectronic properties for nurturing the thermoelectric performance. Annealing induced microstructural modifications instigated the preferential crystal growth by regulating the surface morphology. Low thermal conductivity is credited to strong phonon scattering leading to improved thermoelectric performance. Consequently, we attain a record Seebeck coefficient of ∼270 μV/K and power factor of ∼20 μW/(m·K²) that is almost two-order of magnitude higher as compared to conventional p-type transparent TE materials, indicating the potential of transparent γ-CuI thin films regarding its practical applicability in transparent thermoelectric devices.