Effects of spectrum on the power rating of amorphous silicon photovoltaic devices

The effects of different spectra on the laboratory based performance evaluation of amorphous silicon solar cells is investigated using an opto-electrical model which was developed specifically for this purpose. The aim is to quantify uncertainties in the calibration process. Two main uncertainties arise from the differences in the test spectrum and the standard spectrum. First, the mismatch between reference cells and the measured device, which is shown to be voltage dependent in the case of amorphous silicon devices. Second, the fill factor of the device is affected by different spectra. Different cell structures and states (specifically different i-layer thickness and levels of degradation) for the different light sources are investigated in this work. These sources are different solar simulators, LED sources, Tungsten as well as the standard terrestrial AM1.5G radiation. It is shown that the performance cannot be evaluated by short circuit current alone. The voltage dependent quantum efficiency of p-i-n devices can introduce a mismatch in the PMPP of 1% for 250nm i-layer devices in as prepared state, rising to up to 4% for the 600nm i-layer devices at degraded state.