This work reports Ag-doped Sb 2 Te 3 (A-ST) thin films synthesized by DC magnetron sputtering method onto SiO 2 (SO) and polyimide (PI) substrates based on atomic composition optimization. The effect of post-depositional rapid thermal annealing on the crystallinity, morphology, composition, and thermoelectric properties of thin films was investigated. It was found that thin films on crystalline SO substrate yielded higher crystallinity and eventually a higher thermoelectric power factor in comparison to those grown on a polyimide substrate. The maximum room-temperature power factors achieved were 0.53 mW m À1 K À2 (PI) and 3.95 mW m À1 K À2 (SO).