Broadband asymmetric light transmission interfaces for luminescent solar concentrators

Luminescent solar concentrators (LSC) are actively researched to be incorporated in multi-functional building envelope systems. They consist of a plastic matrix with absorbing-emitting media that guides and concentrates light to edges where solar cells are located. A main drawback of LSCs are escape cone losses at the surface intercepting light. This study investigates trapezoidal nanostructures for creating an interface that enables asymmetric light transmission and reduces these losses. The study employs alumina nanostructures on a PMMA substrate, materials of relevance to LSC applications. The geometry of nanostructures was optimized to maximize asymmetry in the 700nm-1100nm wavelength interval, which corresponds to the range best utilized by silicon solar cells. The multiphysics software COMSOL was utilized to simulate forward (air to PMMA) and backward (PMMA to air) transmission. Spectral transmissivity was calculated for this wavelength interval for a variety of incident polar and azimuthal angles. The largest difference between forward and backward light propagation transmission was found at 720nm, as designed. The forward spectral transmissivity for all polar angles considered was found to be approximately 77% in the 700nm-1100 nm range at an azimuth angle of zero. The backward spectral directional transmissivity in this range was approximately 37%, resulting in a 40% difference. The difference for the entire wavelength range of 400nm-1200nm was approximately 37%. Similar results were obtained when azimuth angle was varied. All these show that the incorporation of nanostructured interfaces can effectively reduce optical losses in LSCs, which will help increase their efficiency. This will make LSCs a more viable solution for use in zero or net-zero energy buildings.