Fabrication and thermoelectric properties of c-axis oriented nanocrystalline Bi2Sr2Co2Oy thin films

•c-axis oriented nanocrystalline Bi2Sr2Co2Oy thin films have been fabricated.•The nanocrystalline films exhibit a large power factor of 0.42 mW/mK2 at 873 K.•A small thermal conductivity is expected in the nanocrystalline films.

c-axis oriented nanocrystalline Bi2Sr2Co2Oy thin films with the average grain size of 25 nm have been achieved by chemical solution deposition combined with a rapid annealing process in oxygen. The resistivity and Seebeck coefficient of the nanostructured films are about 7.0 mΩ·cm and 171 μV/K at 873 K, resulting in a power factor 2–3 times larger than that of the best reported value in the coarse-grained Bi2Sr2Co2Oy polycrystalline bulks. Since the thermal conductivity can be greatly reduced due to the increased phonon scattering at the grain boundaries of nanocrystalline films as well as at film surface and at film/substrate interface, great improvements in the ZT are expected in the nanocrystalline Bi2Sr2Co2Oy thin films.