Polychromic Al-AlN cermet solar absorber coating with high absorption efficiency and excellent durability

Al-N cermet solar selective coatings with double absorbing layers were deposited on Al substrates via a home-made DC magnetron sputter system. The as-deposited coatings showed a high solar absorptance of 0.942 and a normal emittance of 0.066 at 80 °C. Thermal accelerated aging tests results showed that the coatings are durable for at least 25 years. Neutral salt spray test showed that the coating presents excellent corrosion stability because the optical performance (absorptance and emittance) of the coating remained almost unchanged after a 200 h test. The structural, chemical, and optical evolution of the coatings with heat treatment in air was comprehensively investigated. Our research clearly indicated that the as-deposited double cermet layer Al-AlN solar absorber coatings can be used for solar-thermal flat plate collectors. Furthermore, we obtained different colored Al-AlN cermet coatings in a wide range only by tuning the thickness of the Al-AlN (LMVF) and AlN anti-reflective (AR) layers, while maintaining high absorptance (>0.90) and low emittance (<0.10). These coatings are colored blue, purple, red, yellowish orange, and yellow, can be easily produced via a commercial production process, and are suitable for building integration solar energy saving systems.