Investigation of the effects of compressive and tensile strain on n-type bismuth telluride and p-type antimony telluride nanocrystalline thin films for use in flexible thermoelectric generators

To assess the potential performances of flexible thin film thermoelectric generators, we prepared n-type bismuth telluride and p-type antimony telluride nanocrystalline thin films on flexible polyimide substrates using a RF magnetron sputtering method. We applied various compressive and tensile strains to the films by changing the bending radii of the flexible substrates prior to deposition. The structural and thermoelectric properties of the completed samples were analyzed. The bismuth telluride and antimony telluride thin films had dense granular and a chaff-like surface morphologies, respectively. The shapes of both types of films did not greatly change when strains were applied. Both types of thin films demonstrated higher electrical conductivities when under compressive strain than when under tensile strain. The absolute Seebeck coefficients of the bismuth telluride thin films were slightly higher when under tensile strain than when under compressive strain. In contrast, the antimony telluride thin films demonstrated the opposite trend, having higher values when under compressive strain than when under tensile strain. The power factors of both types of thin films were found to decrease with increasing tensile stain. Therefore, we expect that the thermoelectric performances of flexible thin film generators are not largely changed under compressive strain but they decrease under tensile strain. (C) 2015 Elsevier B.V. All rights reserved.