Broadband tunable absorption based on phase change materials

Tunable absorbers have been the subject of many studies in recent years. However, broadband tunable absorbers, which are promising in many applications such as photovoltaic and daytime radiative cooling systems, have not been extensively explored. In this paper, we propose a 2D periodic circular truncated cones nanostructure based on Ge2Sb2Te5 (GST) for regulating broadband absorption. When the phase of GST changes between crystalline and amorphous, the absorption can be effectively tuned over a broad bandwidth. Numerical results show that the average absorption can reach 0.968 at the crystalline phase of GST, but only 0.020 at the amorphous phase of GST in the wavelength from 8 to 15 μm. In addition, the robustness of our proposed structure to the incident angles of the incident wave is also confirmed. The physical mechanism can be explained by the effective medium theory. The magnetic field at different wavelengths are presented for a more intuitive understanding. We believe the structure proposed in this work is promising in the applications of radiative cooling and thermal camouflage.