Formation, structure, and optical properties of copper chromite thin films for high-temperature solar absorbers

CuCr2O (4) thin films grown by physical vapour deposition were studied in order to evaluate their potential as absorber material for the next generation of concentrated solar power plants. A series of Cu-Cr-O thin films was deposited by reactive ion beam sputtering. The Cr/Cu ratio in the sputter target is demonstrated as the most important parameter to achieve the intended film stoichiometry. In-air annealing at 800 degrees C leads to structural transformations of the as-deposited films and results in phase compositions according to those expected from the ternary Cu-Cr-O phase diagram. Tetragonal CuCr2O4 with 98.6 at.% phase purity regarding the solid film constituents is obtained for the appropriate Cr/Cu ratio in the sputter target. CuCr O-2(4) thin films absorb light in the entire solar spectral range from 300 to 2500 nm. Their energy gap is found to be < 0.5 eV, and their solar absorptance is estimated to be (0.85 +/- 0.03). The dense microstructure with good thermal conductivity, full adhesion to the substrate, and a relatively low surface roughness are discussed as technological advantages of CuCr2O4 thin films grown by physical vapour deposition.

Automated summary

CuCr2O4 thin films grown by physical vapour deposition show high phase purity and absorb light in the entire solar spectral range from 300 to 2500 nm. The energy gap of the films is found to be < 0.5 eV, and their estimated solar absorptance is 0.85.