Durability tests and up-scaling of selective absorbers based on copper–manganese oxide deposited by dip-coating

Selective absorbers based on copper–manganese oxide were prepared by dip-coating method. The optical properties of the 2-layer configuration (Al/CuMnOx/SiO2) were improved by introducing an additional absorber-protective layer directly in contact with the aluminium substrate (i.e. 3-layer absorber), for which solar absorptance up to 0.950 was achieved. Long-term durability of these absorbers was investigated by applying both thermal stability and humidity tests established by the IEA-SHC Task X. All the analyzed samples qualified for both tests leading to similar or even better results than some commercial absorbers. In order to prove the feasibility of the up-scaling process, 3-layer absorber samples of 30×30 cm2 size were prepared. It was observed that sintering process was determinant for obtaining fully homogenous films within the whole large-area surface. By using a sintering process with increasing temperature, 30×30 cm2 samples with αs=0.935±0.005 (100 measurements) could be obtained. This study reveals that it is possible to deposit CuMn-oxide absorbers on large-area substrates and that they could be a good alternative to the materials present today in the market, not only in terms of optical properties but also in terms of long term durability.