Voltage-dependent quantum efficiency measurements of amorphous silicon multijunction mini-modules

Multi-junction solar cells have the potential to provide higher efficiencies than single junction devices and to reduce the impact of Staebler-Wronski degradation on amorphous silicon (a-Si)devices. They could, therefore, reduce the cost of solar electricity. However, their characterization presents additional challenges over that of single junction devices. Achieving acceptable accuracy of any current-voltage calibration requires correction of the current-voltage data with external quantum efficiency measurements and spectral mismatch calculations. This paper presents voltage dependant EQE curves for both single junction and double junction a-Si solar cells, along with dispersion curves extracted from these data. In the case of single junction a-Si devices the mismatch factor is known to be voltage dependent and a similar trend is shown to apply to multi-junction devices as well. However, the error introduced into current voltage calibrations due to this bias dependence is found to be < 1% for spectral mismatch calculations.