Progresses in Potential Spectrally Selective Absorbing Coatings for Ultra-High-Temperature (≥600 °C) Solar Thermal Generation

Abstract Concentrated solar power (CSP) technology offers advantages including clean operation, zero pollution, high energy conversion efficiency, and the capability of 24-hour continuous power generation via large-capacity thermal energy storage; consequently, its installed capacity has grown dramatically in recent years. Spectrally selective absorbing coatings (SSACs) are the key functional materials for solar-to-thermal conversion, and their optical performance and thermal stability directly determine the power generation efficiency and the service life of CSP systems. Increasing the operating temperature of CSP systems is well known to significantly improve power generation efficiency and reduce costs. Therefore, to support the future development of ultra-high-temperature (≥600 °C) CSP technologies such as supercritical CO2 cycles, exploring potential SSACs that can withstand temperatures above 600 °C and exhibit excellent photothermal conversion efficiency has become a paramount research topic. This work reviews the research progress on the most promising ultra-high-temperature SSACs using a temperature-graded framework covering 600, 700, 800, and 900 °C. It discusses material selection, multilayer configuration, optical performance, thermal stability, and the intrinsic mechanisms underlying coating failure at high temperatures, thereby providing a reference for subsequent research and engineering applications. The practical implications for CSP plant operation are also discussed, including thermal cycling effects, service-life prediction, and the gap between laboratory-scale stability and real-world field performance.