High temperature efficient, stable Si wafer-based selective solar absorbers

Creating selective solar absorber systems using simple, stable structures capable of surviving high temperatures is essential for widespread adoption of efficient, high-temperature solar thermal technologies. In this study, semiconductor-metal tandem selective solar absorbers based on commercially available Si wafers are fabricated and measured at different high temperatures. High selectivity of the devices is obtained at temperature as high as 490 °C, and the structure is demonstrated to be mechanically and thermally stable even at slightly higher temperatures (up to 535 °C). Increased free carrier absorption and lattice absorption of Si are observed at elevated temperatures, which raise thermal re-radiation dramatically. In order to mitigate this effect, a thin Si film-based selective absorber has also been computationally designed and optimized, which is predicted to exhibit even higher thermal transfer efficiency (60–70%) at a wide range of solar concentrations (20–100 suns). The simple structure combined with the mechanical and thermal stability enables the low-cost Si substrate-based selective solar absorber to find wide applications in solar thermal energy conversion systems.