MXene-Cs₂TiCl₆ perovskite hybrid metamaterial absorber with near-perfect broadband solar absorption for photothermal and photovoltaic applications

A broadband and lead-free MXene-perovskite metamaterial solar absorber made of tilted T-shaped Au resonators has been proposed and analyzed numerically for integrated solar energy harvesting applications. The device is composed of Au/Cd 0.5 Zn 0.5 S/MXene/Cs 2 TiCl 6 /NiO/Au stacked layers with a working range of 0.3 μm to 3.3 μm. It is found that the optimized design shows absorption higher than 90% over the major part of the analyzed range of wavelengths for transverse electric and transverse magnetic polarization, with an AM1.5-solar absorption of 97.89%. The high-absorption bandwidth for the first and second cases over 90% equals 2.91 μm and 2.28 μm, respectively, and the absorption remains stable with respect to changes in polar and azimuthal incident angles. The thermal radiation efficiency is 95.40% at 600 K and 97.35% at 2100 K. The k-nearest neighbors, random forest, AdaBoost, and gradient boosting machine learning methods have been used to predict the absorber's absorption performance, and the gradient boosting regression shows an R 2 value close to unity, including predictions for an unseen parameter combination in the design space. The integrated photovoltaic study gives an output of a short-circuit current density of 18.55 mA/cm 2 and a power conversion efficiency of 19.57%. Additionally, an analysis of fabrication feasibility for the multilayer stack and tilted T-shaped gold resonator is carried out based on realistic limitations. This proves the possibility of integrating broadband solar absorption, photovoltaic performance, and machine learning-based design into a lead-free metamaterial solar energy system.