Effect of microstructure on the thermoelectric properties of CSD-grown Bi2Sr2Co2Oy thin films

Three Bi2Sr2Co2Oy thin films with different microstructures have been prepared by chemical solution deposition on LaAlO3(001) through varying the annealing temperature. With the decrease in the annealing temperature, both the size and c-axis alignment degree of grains in the film decrease as well, leading to an increase in the film resistivity. In addition, the decrease in the annealing temperature also results in a slight increase in the Seebeck coefficient due to the enhanced energy filtering effect of the small-grain film. The nanostructured Bi2Sr2Co2Oy film with an average grain size of about 100 nm shows a power factor comparable to that of films with larger grains. Since the thermal conductivity of the nanostructured films can be depressed due to the enhanced phonon scattering by grain boundary, a higher figure of merit is expected in Bi2Sr2Co2Oy thin film with grains in nanometer size.