Ultrahigh Thermoelectric Performance in SrNb_0.2Ti_0.8O₃ Oxide Films at a Submicrometer-Scale Thickness

Localized refrigeration and power generation via thermoelectric technology rely on efficient thermoelectric materials with high performance at room temperature. Although the two-dimensional electron gas (2DEG)-related materials exhibit ultrahigh thermoelectric performance near room temperature, such performance is only preserved at thicknesses within subnanometer scales, limited by the requirement of two-dimensional size confinements. Here we report ultrahigh thermoelectric performance similar to 2DEG-related materials but achieved in SrNb_0.2Ti_0.8O₃ oxide films with a submicrometer-scale thickness by regulating strain-induced lattice polarizations and interfacial polarizations. A large figure of merit, zT, and power factor (∼10²-10³ μW cm^-1 K^-2) were achieved near room temperature, and the maximum zT is estimated to be ∼1.6 for a 49 nm thick film. These performances exceed those of the existing n-type thermoelectric materials for room-temperature uses and the reported best oxide materials beyond subnanometer scales. The earth-abundant elemental composition of the oxide film paves the way toward potential applications in thermoelectric thin film devices with a microscale thickness.