Efficiency of concentration photovoltaic cells governed by luminescence processes

Abstract

The development of multi-junctions III-V semiconductors solar cells, that combine high conversion efficiency (over 40%) and capability of working under high illumination intensity (up to 1000 suns), has stimulated a rapid growth of concentrating photovoltaic (CPV) technology. The performance of these cells is based on the matching between the semiconductors band gap and the solar spectrum so as to optimize the current balancing between the subcells. This requirement is also important in connection with the CPV modules using lenses, mirrors, optical coupling compounds that introduce a wavelength dependent response to the sunlight. Therefore, care must be exercised in designing optimum cells and optical components for the CPV system configuration. In this work we study the optical and electric properties of multi-junctions InGaP/InGaAs/Ge solar cells during operation in a CPV system. Their reliability is measured by temperature dependent I-V tests. Time-resolved photoluminescence spectra acquired under IR-visible-UV laser excitation allow us to detect the luminescence from the e-h radiative recombination of each junction. Moreover, with the aim to reduce the non-radiative losses, we have tested a down converter based on silica nanoparticles that, under UV excitation, exhibit an emission centered around 2.8 V with lifetime of few ns.