Optical and Thermal Characteristics of Zr-O Solar Selective Coatings

Abstract

Zr-O (Zr-ZrO2) cermet solar selective coatings with a double cermet layer film structure on Al-coated glass substrates for solar collectors used at in high temperatures were prepared by using direct-current magnetron sputtering technology. The typical film structure from the surface to the bottom substrate was an Al2O3 anti-reflection layer on a double Zr-O cermet layer on an Al-metal infrared reflection layer. The deposited Zr-O cermet solar selective coatings had a solar absorptance of α = 0.94 – 0.96 and a thermal emittance of e = 0.07 – 010 (100 ◦C), depending on the sputtering conditions. The absorption layers of the Zr-O cermets coatings on glass and silicon substrates were identified as being amorphous by using X-ray diffraction. Surface roughness measurements of coating layers by using atomic force microscopy showed that the cermet films were very smooth and that their root-mean-square roughness (rms) was approximately 0.1 nm. The composition of the cermet coatings was determined by using X-ray photoelectron spectroscopy. A chemical shift of the photoelectron binding energy occurred due to a change in the structure of the deposited Zr-O cermet coating with increasing oxygen flow rate. The results of the thermal stability test for the thermal characteristics analysis showed that solar selective coating of the Zr-O cermet was stable at temperatures under 350 ◦C.