Optical properties and thermal stability of CrxOy/Cr/Cr2O3 multilayer absorber coatings for solar selective applications

摘要

Spectrally selective CrxOy/Cr/Cr2O3 multilayer absorber coatings were deposited on copper (Cu) substrates using a pulsed sputtering system. The Cr targets were sputtered using asymmetric bipolar-pulsed DC generators in Ar+O2 and Ar plasmas to deposit a CrxOy (bottom layer)/Cr/Cr2O3 (top layer) coating. High absorptance (0.899-0.912) and low emittance (0.05-0.06) was achieved by optimizing the composition and thicknesses of the individual layers. In order to study the thermal stability of the CrxOy/Cr/Cr2O3 coatings, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The coating deposited on Cu substrates exhibited high solar selectivity (/) of 0.895/0.06 even after heat-treatment in air up to 300 °C for 2 h. In the case of vacuum annealing, for temperatures greater than 500 °C the outward diffusion of Cu was the dominating degradation mechanism. Studies on the accelerated aging tests indicated that the absorber coatings on Cu were stable in air up to 250 h at 250 °C with a solar selectivity of 0.898/0.11