Characterization of copper–manganese-oxide thin films deposited by dip-coating

Thin films of copper–manganese oxide were prepared by dip-coating method and annealed between 400 and 500 °C for periods of time from 15 to 90 min. The influence of both annealing time and temperature on film composition and optical properties was studied. X-ray photoelectron spectroscopy (XPS) measurements indicated that the initially formed mixture of copper and manganese oxides leads to Cu1.5Mn1.5O4 through a solid state red-ox reaction. This reaction takes place at temperatures higher than 450 °C and the full conversion of single oxides into Cu1.5Mn1.5O4 needs at least 60 min to proceed. In relation to the optical properties we found that low solar absorptance (αs∼0.6) can be associated with the mixture of single oxides whereas the formation of Cu1.5Mn1.5O4 dramatically increases solar absorptance values (αs∼0.9). The presence of Mn3+ and Mn4+ in octahedral sites and Cu+ and Cu2+ in tetrahedral sites is also evidenced by XPS and can explain the high conductivity of films where Cu1.5Mn1.5O4 is present.