Chromium-based high-temperature selective solar absorber

Selective solar absorbers play a pivotal role in harnessing renewable energy sources and offer considerable potential for efficient photothermal conversion. However, most highly efficient solar selective absorbers require complex structural designs or combinations of multiple materials to implement. Here, we design a spectrum selective solar absorber using only chromium, featuring a cross-shaped square cavity structure. The absorber exhibits a total solar absorption of 96.2% while maintaining a total emissivity of 12%. The distributions of electric field indicate that the outstanding spectrum absorption is caused by the synergistic interplay between surface plasmon resonance, cavity resonance, and guided mode resonance. Our study delves into how different geometric parameters influence the spectrum absorption of the absorber. Additionally, we investigate the performance of the selective solar absorber in terms of absorption at various angles of incidence. Remarkably, even at a substantial angle of 60°, it sustains a high absorption of approximately 80%. At 100°C, the absorber achieves an 86% photothermal conversion efficiency. Furthermore, as the concentration factor increases, the impact of high temperature on the absorber’s photothermal conversion efficiency diminishes. When the concentration factor is 200, the absorber achieves a steady-state temperature exceeding 753°C. This work holds importance in photothermal conversion and thermophotovoltaics.