Insights into the solar spectrally selective absorption performance of anodic alumina photonic crystal films electrodeposited with cobalt and silver: Silver content dependence and the mechanisms

Abstract

Degradation of performance at elevated temperatures is a common challenge encountered by anodic alumina solar spectrally selective absorption films. In this work, anodic alumina photonic crystal films sequentially electrodeposited with Co and Ag nano-particles were prepared. The photonic crystal structure of the anodic alumina part and the nano-particle morphology of the electrodeposited metals were characterized. The solar spectrally selective absorption properties of the films were investigated with respect to the electrodeposition time of Ag and thermal annealing history of the films. Moreover, the surface chemical states of the Co and Ag in these films were examined by X-ray photoelectron spectroscopy. The contents of the Ag electrodeposited into the films were increased approximately linearly with prolonging its electrodeposition time until 250 s and then leveled off. The properties of the films were moderately improved with increasing Ag content, while the degradation of the properties incurred by thermal annealing was substantially alleviated. Various species on the surface of the Co in the films with different thermal annealing histories were identified and quantified, with respect to which the Ag content dependence of the solar spectrally selective absorption performance of these films was explicated. The optimal Ag electrodeposition time was ascertained to be 250 s, corresponding to an Ag content of ∼ 0.25 mg/cm², by balancing the performance of the films and efficiency of the preparation process. The values of spectral selectivity of the resulting film were 7.75 and 5.80 before and after being annealed at 300 °C in air for 24 h, respectively.