Calculation of the Performance of Solar Cells With Spectral Down Shifters Using Realistic Outdoor Solar Spectra

Spectral down converters and shifters have been proposed as a good means to enhance the efficiency of underlying solar cells. In this paper, we focus on the simulation of the outdoor performance of solar cells with spectral down shifters, i.e., multicrystalline silicon solar cells with semiconductor nanocrystals as wavelength-shifting material. Daily and annual performance of these devices can be simulated using spectra that vary over the course of the day. However, as these spectra are not systematically measured, we have employed a spectrum simulation model that is able to simulate clear and also cloudy days: SEDES2. Through the availability of experimentally determined global, direct, and diffuse irradiation data on a minutely basis, we were able to model a full year of spectra for the Netherlands. These spectra are aggregated to yield hourly spectra, which are subsequently used in modelling the solar cell output. We have determined the performance of spectral converters for a number of typical days: a clear summer day, a cloudy summer day, a clear winter day, and a cloudy winter day. It was found that the simulated short current enhancement, which varies between about 7 and 23%, is linearly related with the average photon energy of the spectra. As this is also found to hold for monthly averaged spectra, we were able to calculate an annual performance increase of 12.8% for the present down shifting layer on top of multicrystalline solar cells in the Dutch climate.