Polyhedral Specular Reflector Design for Ultra-High Spectrum Splitting Solar Module Efficiencies (>50%)

Abstract

One pathway to achieving ultra-high solar efficiencies (>50%) is employing a spectrum splitting optical element with at least 6 subcells and significant concentration (100-500 suns). We propose a design to meet these criteria, employing specular reflection to split and divide the light onto appropriate subcells. The polyhedral specular reflector incorporates a high index parallelepiped with seven subcells. The subcells are placed around the parallelepiped such that light entering at normal incidence encounters the subcells in order from highest to lowest bandgap, with the ray path reflecting at a 90° angle until the light is fully absorbed. Previous studies of the design have shown that concentration and filters are necessary to achieve high efficiencies and thus the current iteration of the design employs shortpass filters and two stages of concentration. Ray tracing of the current iteration shows exceeding 50% efficiency is possible for current subcell qualities with perfect shortpass filters while 50% module efficiencies are only possible for very high quality (>6% ERE) subcells with commercially available shortpass filters. However, even with commercially available filters and achievable subcell quality, ray tracing results show very high (>43%) module efficiency.