Design of a high performance selective solar absorber with the structure of SiO2 -TiO2 -TiNxOy -Cu

Abstract

Using TiNxOy thin film as the absorbing layer, a spectrally selective solar absorber (SSA) with the structure of SiO2-TiO2-TiNxOy-Cu has been designed; and the SSA performance has been evaluated by both calculation and experiment. The TiNxOy layer is fabricated by RF magnetron sputtering of a pure TiN target with Ar and N2 gases. The introduction of oxygen in the TiNxOy is realized by using the residual oxygen in the deposition chamber. It is found that the N2 flow rate has a large effect on the complex refractive index of the TiNxOy thin film and thus the SSA performance can be optimized by controlling the N2 flow rate. With the TiNxOy absorbing layer deposited with the N2 flow rate of 2 sccm, the SSA achieves the highest solar thermal conversion efficiency for a solar radiation concentration factor of equal to or larger than 5. The SSA based on the TiNxOy layer deposited with the N2 flow rate of 2 sccm has a solar absorbance of 96.29% and a thermal emittance of 6.11% at the temperature of 400 °C.