Re-defining Non-tracking Solar Cell Efficiency Limits with Directional Spectral Filters

Optical filters that respond to wavelength and direction of incident light have previously been shown to increase the efficiency of tracking solar cells. However, as tracking solar cells are more expensive to install and maintain, it is likely that non-tracking solar cells will remain the main product of the (terrestrial) solar cell industry. Here we demonstrate that wavelength and directionally selective filters can also be used to increase the efficiency limit of non-tracking solar cells at the equator beyond what is currently understood by up to ~ 0.5 % (relative ~ 1.8 %). We also reveal that such filters can be used to regulate the energy output of solar cells throughout a day or year, and can reduce the thickness of the absorber layer by up to 40 %. We anticipate that similar gains would be seen at other latitudes. As this form of angularly selective filter has complex wavelength-angle functionality, we present a proof-of-concept design to realise an angular filter of this type based on Luneburg lenses. Our results will enable further increases in solar cell efficiency, more stable output and more efficient material use.