###### Abstract
Various types of coatings have been researched for their high photothermal efficiency, including semiconductors, cermets, multilayer coatings, textured surfaces, and dielectric-metal-dielectric stacks. Several coatings are now employed as solar selective absorbers for high-temperature operation in solar PTCs: Ni-SiO\({}_{2}\), AlNi-Al\({}_{2}\)O\({}_{3}\), NiCo\({}_{2}\)O4, Pt-Al\({}_{2}\)O\({}_{3}\), Mo-Al\({}_{2}\)O\({}_{3}\), Ni-5 Al, TiAlON/Si3N4/TiAlN, W-Al\({}_{2}\)O\({}_{3}\), Au-MgO, HfMoN/HfON/Al\({}_{2}\)O\({}_{3}\), TiAlN/TiAlON/SiO\({}_{2}\), Ni-25 graphite, and Mo-SiO\({}_{2}\)[25; 26]. Ceramets are the most used selective coatings in solar PTCs. Sandia National Laboratories is currently researching solar selective coatings for lower systems to improve their optical properties [27]. Various coatings have demonstrated absorptivity exceeding 90% at temperatures of 600 \({}^{\circ}\)C and 700 \({}^{\circ}\)C [28; 29]. Notably, thermal spray coatings applied with a laser have shown superior properties, maintaining performance for up to 490 h [30]. To achieve optimal absorbance, the coating should absorb as much solar radiation as possible, with an absorptance of \(\alpha\geq 0.95\)[30]. Consequently, the reflectance of solar radiation should be minimized. Additionally, heat loss through convection, conduction, and emission (with \(\varepsilon\leq 0.05\)) should be kept to a minimum (see Figure 2). Significant efforts have been directed towards developing selective absorbing coatings with improved performance and higher thermal stability at elevated temperatures. This advancement primarily relies on the thermal and structural stability of both individual and integrated layers, strong inconstancy amongst adjacent layers and the substrate, and improved resistance to heat and mechanical stresses. [PERSON] et al. [26] published a review article on the high-temperature applications of STSCs, emphasizing improvements in optical and thermal characteristics, photothermal efficiency, and thermal stability. It highlighted innovative selective absorbing coatings, including combinations of intrinsic (mass), cermet, semiconductor, multilayer interference stacks, and textured surfaces. [PERSON] et al. [24] summarized the structures of STSCs incorporating nanomaterial-based integrations, applied through the front side, back side, or mixed layers to augment solar conversion effacity. The review highlighted the effects of various operational temperature ranges on different coating types, as well as their optical properties, deposition processes, and thermal stability. [PERSON] et al. [31] reviewed the application of carbides and borides as intrinsic STSCs to enhance absorptivity via the solar spectrum. They concluded that the thermal stability of STSCs can be improved by (i) utilizing non-metallic substrates, (ii) diffusion layer deposition over the substrate, and (iii) incorporating a thin layer of proper lanthanum and boron oxides into the interface of the layers. Over the last few years, a variety of diversified techniques have been established to develop and improve the tractability of STSCs. However, achieving the desired spectral selectivity and high-temperature stability poses several challenges, despite the extensive use of their bulk counterparts in ultra-temperature applications as previously mentioned. This paper introduces a critical review of recent and past advances in the technical applicability and potential of STSCS. Initially, a brief review of the classifications, theories, and principles of different STSC configurations is introduced, assessing their individual weaknesses and strengths. Then, this paper critically summarizes the technological advancements, types  
Figure 2: Schematized view of a perfect STSC. of STSCs, preparation methods, and aging mechanisms for improving the solar conversion performances of STSCs.