## 3 Recent Advances in Different Configurations of STSCs
### Cermet Composite STSCs  
Double cermet STSCs are composed of grouped metal particles within a dielectric matrix. The production process involves inseminating metal molecules into ceramic bases or porous oxides. Ceramic-metal coatings (cermets) are the most common choice for CSP applications [58]. While simple one-layer cermet is effective, more sophisticated layered structures have been developed. The example shown in Figure 6 features an anti-reflective coating, incorporating cermet layers with varying fractions to absorb shortwave radiation and a metal layer to reflect infrared radiation. In these coatings, the low-metals-based cermet serves as the lowest absorptance thin film, while the large-metals-based cermet layer functions as the highest absorptance thin film [59]. AIN- and Mo-SiO\({}_{2}\)-based ceramics were recently utilized by Turbosun, Shenzen(China),and Massa Martana, Angelantony (Italy), respectively, in the commercial sector [60]. However, their thermal emissivity at high temperatures tends to exceed 10%, particularly after annealing. With advancements in cermet layers, the thermal stability of certain STSCs now reaches 600 \({}^{\circ}\)C by management of the metallic component diffusion and improving the heat resistance of the dielectric components. Several cermet coatings incorporate matrices such as AlN, Al\({}_{2}\)O\({}_{3}\), YSZ, AlSiOx, and SiO\({}_{2}\), which provide stability, combined with metal particles like Mo, Ag, W, and Ni [61; 62]. For example, Al\({}_{2}\)O\({}_{3}\) is commonly utilized as a dielectric in cermet STSCs owing to its lowly refractive indicator of 1.65 and moderate thermal stability [63]. Numerous experimental studies and simulation models have examined the optical characteristics of cermet STSCs. These coatings are notable for their superior photothermal conversion efficiency, which is attributed to both the cermet matrix's ability to efficaciously harness solar irradiation and the phenomenon of phase intrusion. [PERSON] et al. [64] prepared a cermet STSC with low emissivity (~3.0%) and high absorptivity (~95%) as the light-absorbing material for their multiple photothermal cycles potential. This design features a light-absorbing layer, a thermal spreader layer, and a thermal insulating layer. The light-absorbing layer effectively transforms incident light into heat energy, the thermal spreader layer ensures even heat distribution, and the thermal insulating layer reduces heat loss to the supercooled metal substrate. [PERSON] et al. [61] experimentally analyzed the optical and mechanical properties of an AlSiOx: W-based solar selective absorber cermet using the sputtering magnetron deposition process. The results indicated that this film architecture possesses a suitable spectral capability, achieving 94.5-95.7% solar absorptivity and 10-14% emissivity at 400 \({}^{\circ}\)C. [PERSON] et al. [65] investigated the spectral selectivity and thermal stability of an STSC with a TiN single-bond SiO\({}_{2}\) cermet. They found that the absorptance of the coatings deposited on LaAlO\({}_{3}\) remained above 94% even after annealing. Additionally, as the substrate temperature increased, the reflectance of ZrO\(\times\)/Al\({}_{2}\)O\({}_{3}\)-SS/ZrC coatings gradually decreased, contributing to high absorptance. [PERSON] et al. indicated that the Pt-Al\({}_{2}\)O\({}_{3}\)-based STSC hat maintained thermal stability at 773 K for 120 h with an absorptance/emittance (\(\alpha/\epsilon\)) ratio of 0.92/0.13 [66]. Meanwhile, [PERSON] et al. doped W and Ni metals into an Al\({}_{2}\)O\({}_{3}\) matrix, achieving an absorptance of approximately 90% at 600 \({}^{\circ}\)C [67]. [PERSON] et al. [46] deposited Al\({}_{2}\)O\({}_{3}\)/Mo-HfC onto stainless steel substrates,  
Figure 6: Structure layers of cermet composite STSC. achieving a spectral selectivity of 0.92/0.11. XPS analysis of the HfC-Mo bonding structure revealed that the incorporation of Mo significantly enhanced the coating's absorptance. [PERSON] et al.