Broadband High-Temperature Multilayer Pyramid-Shaped Metamaterial Thermal Absorber for Thermophotovoltaic applications

Abstract: A broadband, thermally stable absorber is essential for thermophotovoltaic (TPV) systems to simultaneously convert solar and industrial waste heat into usable energy to meet growing power demands. Here, we proposed an ingenious polarization-independent truncated pyramid-shaped symmetric multilayer metamaterial absorber in a metal-insulator-metal-insulator (MIMI) architecture with almost complete absorption over a broad wavelength range. A total of six structures (W/AlN, Mo/AlN, Ta/AlN, Rh/MgO, Rh/SiO2, Re/BN) were designed, and the materials were selected based on their lattice matching to prevent delamination at interfaces between layers. The absorption mechanism was studied at room temperature using the finite difference time domain (FDTD) method, and the structure was optimized through a brute force design approach, which illustrates a best average absorption of 98.2% till 4000 nm and 97.73% till 5072 nm wavelength for the W/AlN structure with metal and dielectric thicknesses of 60 nm and 17.5 nm, respectively. Moreover, W/AlN structure exhibits over 96% average absorption up to 50 degree incident angles irrespective of polarizations. The thermal stability was evaluated using the finite element method (FEM) by determining von Mises stress at elevated temperatures. Thermal analysis revealed that only W/AlN can withstand around 1700 K temperature and 1500 times the incident power before permanent deformation. A temperature-dependent Drude-Lorentz model was used to further analyze the effect of absorption on the optical performance of the highly absorptive and thermally stable W/AlN structure. Additionally, we determined the effect of the concentration factor, and the operating temperature on the system efficiency by considering the emission loss of the heated absorber.