Modelling spectral irradiation effects on single- and multijunction amorphous silicon photovoltaic devices

It has been previously reported that variations in the spectral irradiance under which an amorphous silicon device operates can have a significant effect on its electrical performance, often contributing to enhanced system Yields compared to crystalline-based systems. In this work, spectral irradiance data based on models and measurements taken at the Centre for Renewable Energy Systems Technology (CREST) in the UK are presented. These are input into electrical models for amorphous silicon devices incorporating different number of junctions in order to investigate the impact of changing spectral irradiation. The results can be classified broadly as primary effects, those accounting for the available spectrally useful irradiance and secondary effects that consider the effects of mismatched currents in the stacked cells of multi-junction devices. The modeled short circuit currents correlate well with measurements and are demonstrated as a useful tool for further investigation.