Achromatic lens casting nearly uniform irradiance over MJ solar cells

Abstract

The Achromatic Doublet on Glass (ADG) Fresnel lens is a novel concentrator that combines a low-dispersion elastomer and a high-dispersion plastic to obtain a Fresnel lens with reduced chromatic aberration, and consequently, increased concentration capability. This article summarizes the outcomes of the ray-tracing simulations as well as the experimental results obtained within the past two years. In addition, the uniformity of the irradiance profile cast by the lens onto Multi-Junction solar cells is analyzed and compared to that of a classic Silicone on Glass (SoG) Fresnel lens used as a benchmark. The more uniform profile cast by the achromatic lens requires lower horizontal current transportation across the MJ solar cell since the photocurrent distributions for the top and middle subcells are similar. It has been experimentally shown that, although the Fill Factor (FF) of the solar cell illuminated by the SoG Fresnel lens strongly depends on the lens-to-cell distance (showing a characteristic W-shaped curve), for the ADG Fresnel lens, the FF remains high at every position. This implies a higher tolerance not only to errors in the module assembly but also to variations in the temperature of the primary lens.