Ultra-broadband graphene–tungsten–titanium metasurface solar absorber for near-unity absorption and high-efficiency solar thermal energy conversion with machine learning validation

The development of high-efficiency solar absorbers capable of converting broadband solar radiation into thermal energy is essential for advancing solar energy harvesting and supporting renewable and sustainable energy technologies. This study presents the design and electromagnetic analysis of a multilayered metasurface solar absorber combining graphene, tungsten and titanium. The structure consists of three central circular tungsten-coated resonators with diameters of 250 nm, a dual circular graphene-functionalized rings with diameters of 450–500 nm and an outer square tungsten ring measuring 750–800 nm, all mounted on a 3000 nm silicon dioxide dielectric layer with a titanium reflective backing. COMSOL Multiphysics simulations show broadband absorption above 97% across 200–3000 nm, covering ultraviolet, visible and infrared regions. The absorber maintains high absorption up to incidence angles of 80° for TE and TM polarizations, with peak absorption of 99.99% at specific wavelengths. Parametric studies indicate that variations in resonator dimensions and square ring gaps strongly affect absorption, with optimized configurations achieving 97.859%, 95.865% and 96.878% in UV, visible and IR regions, respectively. Electric field analysis shows strong localization with peak intensities of 4 × 10⁷ V/m at resonant wavelengths. A machine learning model trained on simulation data predicts absorption with R² values above 0.97 and mean squared errors below 0.0005, providing an efficient alternative to computationally expensive full-wave simulations. Tunable graphene layers enable resonance modulation through electrochemical gating, while tungsten and titanium ensure thermal stability for prolonged operation. The absorber’s ultra-broadband response, angular robustness, and tunability make it suitable for solar thermal energy harvesting, thermophotovoltaics, desalination, and optical sensing applications.