Design of multilayer planar film structures for near-perfect absorption in the visible to near-infrared

Abstract

In this work, a near-perfect broadband absorber, consisting of Fe, MgF2, Fe, TiO2 and MgF2 planar film, is proposed and investigated through simulations and experiments. The Fe material is first applied in the multilayer film structure, and it is proved to be more favorable for achieving broadband absorption. MgF2 and TiO2 are chosen as anti-reflection coatings to decrease unwanted reflections. The proposed absorber is optimized by employing a hybrid numerical method combining the transfer matrix method (TMM) and the genetic algorithm (GA). Under normal incidence conditions, the average absorption of the absorber is 97.6% in the range of 400 to 1400 nm. The finite difference time domain (FDTD) method and phase analysis reveal that the anti-reflection property and the Fabry-Perot resonance result in broadband absorption performance. Furthermore, when an additional Fe-MgF2 layer is inserted on the bottom Fe layer, an average absorption of 97.9% in the range of 400 to 2000 nm can be achieved. Our approach could be of vital significance for numerous applications involving solar energy.