Alternative Model of a Subwavelength Diffractive Lens Proposed for PV Cells Applications

Recently, several approaches have been proposed to concentrate and to separate spectrum bands of sunlight using a planar design. Fresnel lenses are widely used in concentrating photovoltaic systems, to achieve the concentration of sunlight onto the surface of solar cells. A diffractive lens superimposed with a grating, in a single integrated optical device, has been proposed to obtain the sunlight spectrum splitting and beam concentration (SSBC) simultaneously. Here, we present an alternative approach to achieve SSBC functionality using only a diffractive lens. Because of the subwavelength structures used, a high efficiency for a broadband light spectrum is demonstrated through simulations. We propose a theoretical model for a subwavelength diffractive lens (SWDL), which has been elaborated with optimal parameters. The model proposed is suitable to be used for low concentration (1-10×) PV cell systems. The optical efficiency obtained is ~70% after separating apart of the sunlight spectrum (400-1100) nm into two bands (400-800) and (800-1100) nm. A new electromagnetic modeling tool based on a hybrid finite difference time domain angular spectrum method propagator has been used to analyze the performance of the proposed model. The proposed SWDL achieves the functionality of an SSBC over a small distance and can be integrated into a compact PV cells system.