Bandgap Optimization of Photovoltaic Tandem Cells Based on Spectra Collected over a Full Year

Abstract

Spectral data collected every minute at the test station in Grimstad, Norway, are used to investigate the impact of spectral variation on tandem cells. The results are displayed as efficiency maps which are compared to equivalent maps for the air mass 1.5 global (AM1.5G) reference spectrum. Most of the maps are calculated for ideal cells and will thus serve as benchmarks for what can possibly be achieved under real conditions, but the impact of non-radiative recombination is also included. It is found that there is generally good agreement between the efficiency under the AM1.5G spectrum and the efficiency found using the collected spectra. The main difference is that a slight blueshift in the real spectra favors larger bandgaps. Seasonal efficiency maps and maps for different types of conditions are also presented. The largest deviation from the reference spectrum is found for the three darkest months of the year. Optimizing the bandgaps for this period may increase seasonal production by several percent, albeit with a significant accompanying reduction in annual production. For June, the sunniest month, as well as for cloudy and lowlight conditions, it is found that the optimal bandgaps are slightly larger than those found for the AM1.5G.