Reducing shadowing losses with femtosecond-laser-written deflective optical elements in the bulk of EVA encapsulation

A new approach on decreasing the optical shadowing of the solar cell grid fingers is presented. The approach relies on a local change of the optical properties in the bulk of the photovoltaic module encapsulation material ethylene vinyl acetate (EVA). In particular, scattering and diffractive optical elements are locally generated within the volume of cross-linked EVA encapsulation material by applying a femtosecond-laser-writing process. When these optical elements are located above the metal grid fingers, the optical shadowing of these grid fingers can be decreased. In an experimental proof of concept, the optical performance of this approach is demonstrated. The best results obtained so far indicate a decrease in optical shadowing by 17%. The material characteristics of the volume optics were investigated by applying confocal Raman microscopic characterisation, which indicates that the EVA material partially degraded upon the impact of the laser beam and is partly carbonised. Supplementary optical simulations show that the light deflection is caused by diffraction. However, parasitic absorption substantially deteriorates the optical performance of the deflective volume optics. Copyright © 2014 John Wiley & Sons, Ltd.