High Temperature Spectrally Selective Solar Absorbers Using Plasmonic AuAl₂:AlN Nanoparticle Composites

Advanced solar energy collectors require the use of thermally stable and spectrally selective coatings in order to boost absorption of radiant energy. Here, it is shown that incorporation of plasmonically resonant Au and AuAl₂ nanoparticles into multilayer coatings based on AlN provides strong and stable absorption across the solar spectrum at temperatures between RT and 500 °C. Optical properties at operating temperature are verified using in situ measurements. Solar absorptance of 92–97% is available in the as-deposited films, which are comprised of layers of Al, Au:AlN, AlN, and SiO₂. Annealing at the operating temperature of ∼500 °C causes the conversion of the elemental Au to the intermetallic compound AuAl₂, but the good solar absorbing performance is retained. The additional Al that reacts with the Au nanoparticles to form the AuAl₂ diffuses up from the reflective Al substrate used. Enhanced NIR solar absorptance post-annealing is accompanied by a tolerable small rise in thermal emittance. Formation of AuAl₂:AlN also prevents undesired Au nanoparticle agglomeration above 500 °C. This suggests that AuAl₂:AlN nanoparticle composites are excellent candidates for solar thermal applications up to about 500 °C.