Abstract: P-type telluride materials, mainly Bi_xSb_2-xTe₃, have been the focus of thermoelectric research owing to their high performance and low cost. However, their high lattice thermal conductivity and narrow application temperature range have limited further development. In this work, a novel medium-entropy thin film with low lattice thermal conductivity was fabricated by alloying Bi, Sb, In, and Te. The film exhibited a low lattice thermal conductivity (approaching 0.2 W m^-1 K^-1) at room temperature (303 K). Subsequently, Ge doping was introduced to optimize thermoelectric properties, resulting in an optimized film with a thermoelectric figure of merit (ZT value) of 0.51 at 393 K. The configurational entropy of this thin film can reach 1.16 R; thus, it can be used as a precursor of bismuth telluride-based high-entropy materials, providing a basis for subsequent high-entropy research.

Key words: Thermoelectric film, Lattice thermal conductivity, Entropy engineering, Microstructure, SEM, TEM