Spectrally selective absorber coating of WAlN/WAlON/Al2O3 for solar thermal applications

A novel WAlN/WAlON/Al2O3 coating was successfully deposited on stainless steel (SS) substrate using reactive DC and RF magnetron sputtering. Excellent spectrally selective property with a high absorptance of 0.958 in the solar spectrum region and low emittance of 0.08 in the infrared region were achieved by tailoring the target power, deposition time and the reactive flow rates of N2 and O2. In the present solar selective coating, W layer acts as a back reflector and diffusion barrier, WAlN as the main absorber layer, WAlON as the semi-absorber layer, whereas the topmost Al2O3 layer works as an anti-reflecting layer. In reference to the thermal stability, the absorber deposited on SS substrates exhibited high solar selectivity (α/ε) of 0.920/0.11, when heat treated in air up to 500 °C for 2 hrs. Taken together, the present study demonstrated that the WAlN/WAlON/Al2O3-based selective absorbing coating with excellent thermal stability could be a promising material for photo-thermal conversion at temperatures of up to 500 °C.