Voltage-dependent quantum efficiency measurements of amorphous silicon multi-junction 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-dependent 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.