Wide-angle multiplexed holographic photovoltaic concentrators recorded in a green photopolymer

Photopolymers are among the most promising materials for recording transparent volume multiplexed holographic lenses (MHLs), which constitute key holographic optical elements (HOEs) in diverse photonic and photovoltaic applications. In this work, the recording performance of a high–dynamic–range, low–toxicity photopolymer (Biophotopol) has been optimized under multiplexing conditions. The concentrations of the dye (riboflavin 5’-monophosphate sodium salt) and the monomer (sodium acrylate) were adjusted to maximize refractive index modulation, while the exposure schedule method (ESM) was implemented to efficiently distribute exposure energy among multiple recordings. Using the optimized formulation, holographic solar concentrators (HSCs) with a spatial central frequency of 500 lines/mm were fabricated. Multiplexed concentrators containing 6, 7, and 8 holographic lenses exhibited average diffraction efficiencies of 80%, 76%, and 63%, respectively, and acceptance angles of 40 \(∘\) , 45 \(∘\) , and 53 \(∘\) under solar–simulated white–light illumination. These results demonstrate that the optimized Biophotopol enables the fabrication of wide–angle, high–efficiency multiplexed holographic concentrators, paving the way toward the development of lightweight, sustainable, and free–tracking holographic photovoltaic systems.