Rapid growth of fully-inorganic flexible CaxCoO2 thin films from a ligand free aqueous precursor ink for thermoelectric applications.

We demonstrate a ligand-free green chemical method for the rapid growth of nanoporous Ca0.35CoO2 thin films on sapphire and mica substrates from a water-based precursor ink, formulated by dissolving the precursor solid, composed of in situ prepared Ca2+-DMF and Co2+-DMF complexes. Mica serves as the flexible substrate as well as the sacrificial layer for the film transfer. Despite the presence of nanopores, the power factor of the flexible film Ca0.35CoO2-on-mica is above 0.50 × 10-4 W m-1 K-2 at around room temperature. The present technique is simple and cost-effective.