Analysis of light collection in GaAs/Si HJT four-terminal solar cell system based on spectral splitting and polymeric wedged optics: a role for diffusive lateral supports

In this work a system combining a GaAs and Si heterojunction cells with optical components in a four-terminal solar cell configuration is presented. This system achieves optical low gain non-imaging asymmetric concentration and spectral splitting in order to enhance energy conversion specific to each cell, and represents a promising pathway to overcome the limitations and improve the efficiency of conventional photovoltaic systems. The split of the solar spectrum is realized by integrating into the system a specifically designed polymeric dielectric prism with light waveguide capability and high transmittance, coupled with a tailored dichroic mirror that reflects wavelengths shorter than 805 nm and transmits longer ones. In view of optimizing its performance, we critically investigate the optical performance of each component and of the system as a whole, at different light source incident angles and different colors of the side covers in a controlled indoor test environment. Moreover, outdoor tests at four fixed system orientation angles and for different side color cover cases have been performed. 4T system efficiency is studied both in indoor with a solar simulator and in outdoor under natural sunlight. The experimental results provide some clear indications to improve the system's performance, highlighting the importance of the incident angle of the source and of color of the covers to boost light collection.