Design of a High Performance Selective Solar Absorber with the Structure of SiO₂-TiO₂-TiN_xO_y-Cu

Abstract

Using TiN x O y thin film as the absorbing layer, a spectrally selective solar absorber (SSA) with the structure of SiO 2 -TiO 2 -TiN x O y -Cu has been designed; and the SSA performance has been evaluated by both calculation and experiment. The TiN x O y layer is fabricated by RF magnetron sputtering of a pure TiN target with Ar and N 2 gases. The introduction of oxygen in the TiN x O y is realized by using the residual oxygen in the deposition chamber. It is found that the N 2 flow rate has a large effect on the complex refractive index of the TiN x O y thin film and thus the SSA performance can be optimized by controlling the N 2 flow rate. With the TiN x O y absorbing layer deposited with the N 2 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 TiN x O y layer deposited with the N 2 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.

Optical Properties and Microstructure of TiNxOy and TiN Thin Films before and after Annealing at Different Conditions

“…Different types of SSA, such as metal-dielectric composite, multilayer absorbers and semiconductor-metal tandems have been developed due to their higher thermal absorbance, higher thermal stability and low IR emittance [3][4][5][6]. In recent years, many types of selective solar absorber coatings for mid-to-high-temperature applications were studied, but only a few of them have been successfully commercialized.…”

“…Many researchers deposited TiN x O y using reactive magnetron sputtering and by changing the (N/O) ratio, with different types of AR layers such as TiO 2 /Si N 4 /SiO 2 and TiO 2 /SiO 2 to obtain efficient SSA [3,4,8]. Chen et al [4] found that the behavior of TiN x O y films was changed from metallic to dielectric behavior by increasing the oxygen content.…”

“…In the case of low N/O ratio, the formed TiN x O y was transparent in the solar spectrum region, while high N/O ratio resulted in metallic behavior and high-reflection TiN x O y thin films [4]. Zhang et al [3] determined the optimum N/O flow rate, which resulted in a solar selective absorber with a high absorbance of 97.55%. Kazemeini et al [8] used DC sputtering reactive process to produce TiN x O y film by using Ti target and O 2 /N 2 ratio of 1/4.…”

“…SS substrate is used because it is considered as the best candidate material for CSP tube fabrication for high-temperature applications. The N 2 /O 2 flow rate used in this work is chosen based on reviewing previous works [3,4] and initial deposition trials. Post-deposition vacuum annealing is adopted in this work as an option for residual stress relief and energy reduction of the sputtered thin films.…”

Structural, Optical and Electrical Properties of Electron Beam Evaporated Tioxny Films as Selective Solar Absorber Coatings

“…TiO x N y have also been investigated as selective solar absorber materials [31,32]. However, the spectral selectivity was achieved by using multi-layer structures and antireflection layers which requires several steps [33][34][35]. In addition, all the reported TiO x N y solar absorber materials have been prepared by using sputtering technique.…”