Optical properties of materials for concentrator photovoltaic systems

As part of our research on materials for concentrator photovoltaics (CPV), we are evaluating the optical properties and solar radiation durability of a number of polymeric materials with potential CPV application. For optical materials in imaging or non-imaging optical systems, detailed knowledge of the wavelength dependent complex index of refraction is important for optical system design and performance. Here we report the index of refraction, optical absorbance and haze results of various polymers of interest for CPV systems. Fluoropolymers such as polyvinylfluoride (Tedlar^? PVF Film), which has wide application in crystalline silicon (c-Si) flat plate PV modules, as well as poly(tetrafluoroethylene-co-hexafluoropropylene) (Teflon^? FEP Film) and poly(ethylene-co-tetrafluoroethylene) (Tefzel^? ETFE Film) have desirable optical and physical properties for optical applications such as CPV. Hydrocarbon polymers such as polyvinylbutyral (PVB) sheet such as DuPont? PV5200, and the ethylene copolymers such as poly(ethylene-co-vinyl acetate) (EVA) such as Elvax^? PV1400, poly(ethylene-co-methacrylic acid metal salt) ionomer sheet such as DuPont? PV5300 have applications as encapsulant in c-Si and other flat plate PV applications. These materials have both a wide variety of polymer compositions and also additive packages, which affect their optical properties such as the UV absorption edge. Even materials such as Kapton^? polyimide films, which are used behind the PV cell for their electrically insulating properties, have optical requirements, and we characterize these materials also. The detailed optical properties of these materials will be useful for CPV system design of the geometrical optics, optimization of the system´s optical throughput, and also provide insights into the system´s optical absorption, for example in the UV, where this absorption can impact the radiation durability of the materials.