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

Abstract

We demonstrate a ligand-free green chemical method for the rapid growth of nanoporous Ca_0.35CoO₂ 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 Ca_0.35CoO₂-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.