Investigation on Thermoelectric Power Factor of Tin–Copper Oxyselenide Nanoscale Thin Films Obtained by the Reactive Magnetron Cosputtering Technique toward Energy Harvesting Applications

The study shows a systematic synthesis approach for incorporation of oxygen and copper into tin selenide (SnSe) for the purpose of achieving SnCuOSe material through a reactive cosputtering technique toward energy harvesting applications such as thermoelectrics. SnSe, SnCuSe (SnSe-Cu), and SnCuOSe (SnSe-Cu-O) nanoscale thin films were fabricated on glass substrates using sputtering, cosputtering, and reactive cosputtering from tin selenide and copper targets. The films were then vacuum annealed at 350 °C. A key focus was characterizing the electrical properties (carrier concentration, mobility, conductivity) and thermoelectric properties (Seebeck coefficient, power factor). The layered structure of the material, comprising covalent chalcogenide layers (charge carrier channels) and ionic oxide layers (charge reservoirs), was beneficial for its potential to optimize electrical properties via lone pairs and enhance thermoelectric power factor through phonon scattering. High-resolution transmission electron microscopy (HRTEM) revealed tensile microstrain in SnSe-Cu-O, which corroborates with analysis from X-ray diffraction (XRD). The highest Seebeck coefficient achieved for SnSe-Cu-O was 56.62 μV/K at 250 °C. Crucially, the power factor of SnSe-Cu-O exhibited a significant temperature-dependent increase, reaching a peak of 2.55 mW/mK2 at 250 °C, the highest among the synthesized materials, SnSe and SnSe-Cu. This demonstrates the beneficial effect of oxygen on the Seebeck coefficient and the overall thermoelectric power factor enhancement in SnCuOSe, making it a promising candidate for thermoelectric applications.