Design and Numerical Analysis of a Fractal Tree Shaped Graphene Based Metasurface Solar Absorber

This study introduces a novel solar absorber design using a fractal tree-shaped graphene-based metasurface. The absorber structure consists of tungsten fractal tree arrays on a graphene monolayer, supported by a silicon dioxide (SiO₂) dielectric layer and a tungsten substrate. The entire unit cell measures 0.5 μm × 0.5 μm × 1.16 μm. Performance simulations using COMSOL Multiphysics v5.6 optimized the physical parameters, demonstrating broadband absorption in the spectrum 400–800 THz, with peaks at 430 THz, 510 THz, 590 THz, 670 THz, and 760 THz, reaching up to 95% absorption. The average absorption efficiency was approximately 90%. The absorber's performance is sensitive to the thickness variations of the fractal tree, graphene layer, SiO₂ layer, and tungsten substrate, stabilizing at higher frequencies. Additionally, the design exhibits significant absorbance variability across incidence angles (20° to 65°), with notable peaks around 450 THz and between 400 and 600 THz. The fractal tree geometry enhances light interaction, while the graphene layer's tunable optical properties contribute to sharp absorption peaks. The SiO₂ layer introduces interference effects essential for effective light absorption. The optimized design offers efficient, angle-insensitive broadband absorption, making it a promising candidate for solar energy harvesting applications.