To cope with the energy crisis and global warming, the continuous development and efficient utilization of renewable energy such as solar power have aroused worldwide interests and been regarded as promising solutions. Solar-thermal energy conversion, which can potentially utilize the full-spectrum sunlight, is a prospective implementations of solar energy harvesting technology with diverse applications such as household and industrial heating/cooling, solar steam generation, and electricity generation. Solar absorbers with great spectral selectivity, excellent thermal stability, and scalability are a key technology in solar-thermal energy conversion systems, especially for those operating at high temperatures. However, most of the state-of-the-art selective solar absorbers (SSAs) can...[ Read more ]

To cope with the energy crisis and global warming, the continuous development and efficient utilization of renewable energy such as solar power have aroused worldwide interests and been regarded as promising solutions. Solar-thermal energy conversion, which can potentially utilize the full-spectrum sunlight, is a prospective implementations of solar energy harvesting technology with diverse applications such as household and industrial heating/cooling, solar steam generation, and electricity generation. Solar absorbers with great spectral selectivity, excellent thermal stability, and scalability are a key technology in solar-thermal energy conversion systems, especially for those operating at high temperatures. However, most of the state-of-the-art selective solar absorbers (SSAs) can only maintain their superior performance below 773 K. To achieve high electricity generation efficiency, it is desperately demanded to develop scalable SSAs that can offer stable and superior overall performance at elevated temperatures (>873 K). The major goal of this thesis is to fill the technology gap and experimentally demonstrate such scalable, highly selective, and thermally stable SSAs for high-temperature solar-thermal energy conversion systems.

Plasmonic metamaterials can offer exotic optical properties that are absent in natural materials, such as negative index and ultrathin light concentration, through strong localized surface plasmonic resonances in metallic nanoparticles. In this study, at first, we introduce triangular nanodisks into the metal-insulator-metal structured plasmonic metamaterials. The resultant plasmonic metamaterials enable highly selective and near-perfect (>95%) light absorption and a strong local electric field enhancement simultaneously, due to the combination of the strong lightning rod effect and the out-of-plane plasmonic coupling. Based on this discovery, we further develope hybrid-strategy (structure-, material-, and shaped-based) plasmonic metamaterials for broadband and selective sunlight absorption by adopting high-loss triangular nanodisks and a tantalum reflector in metal-insulator-metal structure. The obtained scalable SSAs demonstrate full-spectrum sunlight absorption and greatly reduced infrared emission, ultimately leading to a high solar-thermal conversion efficiency of 77.3% under 100-sun illumination and at an operating temperature as high as 1000 K. This superior performance is stable at high temperatures up to 1000 K.

Considering that all the state-of-the-art SSAs are produced by sophisticated nanofabrication techniques using expensive facilities, leading to enormous costs in commercial-scale production. We fabricate low-cost and high-performance SSAs through self-assembly of plasmonic TiN nanoparticles by solution-based processes, exhibiting unprecedented spectral selectivity. Assisted by perhydropolysilazane (PHPS)-derived SiO₂ coatings, high solar absorption (94.0%) and ultralow infrared emission (21.1% at 1000 K) are realized simultaneously in absorbers on TiN reflectors. The SSAs that are thermally stable up to 1000 K after long-term thermal annealing provide a comparable solar-thermal efficiency (82.0% at 1000 K under 100 suns) to that of the best vacuum-deposited absorbers.

Finally, multilayer metal/ceramic nanofilms are promising SSAs owing to their strong sunlight absorption provided by extremely simple configurations and facile fabrication. However, the commercial success of such SSAs is still hindered by their unsatisfactory spectral selectivity and high-temperature stability associated with metal/ceramic interfaces. Here we first propose an all-ceramic TiN/TiNO/ZrO₂/SiO₂, SSA with highly selective absorption, producing an unprecedented solar-thermal conversion efficiency(82.6% under 100 suns at 1000 K). Remarkably, the absorber shows great thermal stability even after long-term (150 hrs) annealing at 1000K, boosting the operating temperature of conventional multilayer absorbers by at least 227 K. The efficient and stable all-ceramic SSAs can be readily produced in quantity via low-cost processes, rendering it attractive for high-temperature solar-thermal technologies.

Keywords: Solar-thermal energy conversion; selective solar absorbers; plasmonic metamaterials; all-ceramic multilayer structure; thermal stability; scalability; superior performance.