  CaxCoO2 thin films can be promising for widespread flexible thermoelectric
applications in a wide temperature range from room-temperature self-powered
wearable applications (by harvesting power from body heat) to energy harvesting
from hot surfaces (e.g., hot pipes) if a cost-effective and facile growth
technique is developed. Here, we demonstrate a time resolved, facile and
ligand-free soft chemical method for the growth of nanoporous Ca0.35CoO2 thin
films on sapphire and mica substrates from a water-based precursor ink,
composed of in-situ prepared Ca2+-DMF and Co2+-DMF complexes. Mica serves as
flexible substrate as well as sacrificial layer for film transfer. The grown
films are oriented and can sustain bending stress until a bending radius of 15
mm. Despite the presence of nanopores, the power factor of Ca0.35CoO2 film is
found to be as high as 0.50 x 10-4 Wm-1K-2 near room temperature. The present
technique, being simple and fast to be potentially suitable for cost-effective
industrial upscaling.
