Design of polymer multilayer heterostructure broadband reflector for the near-infrared using genetic algorithm

A broadband reflector for the near-infrared (NIR) was designed using a multilayer heterostructure consisting of several quarter-wave stacks (QWSs), which were composed of polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET) films. Taking the solar power density as the target and using the Bragg wavelength of each QWS as the variable, the genetic algorithm was applied to look for the optimal multilayer heterostructure for broadband NIR reflection. As high as 99.46% total energy reflectivity in the short-wavelength NIR region (780 to 1100 nm) and 89.56% total energy transmissivity in the visible light region (380 to 780 nm) were realized by a multilayer heterostructure consisting of six quarter-wave PMMA/PET stacks, which can be easily fabricated based on the micronano multilayer coextrusion technology. The designed structure possesses good stability, and its total energy reflectivity is not sensitive to the incident angle of light. The proposed broadband NIR reflector can be applied to buildings as energy-saving films.