Hydrogenated amorphous silicon (a-Si:H) multi-junction devices have demonstrated a way to increase the efficiency of a-Si:H thin-film photovoltaic (PV) modules, which is now well above 10%. Since the current–matching behaviour of all sub-cells is a critical aspect, the measurement of the spectral response (SR) of all junctions provides valuable information to optimize the device performance under a given spectral distribution. In this work the authors investigate the impact of low shunt resistances on the SR of a double-junction a-Si:H/μc-Si PV module. The origin of a low shunt resistance in a-Si:H multi-junction devices is revised. A simple theoretical approach is then used to describe the anomalous dark SR observed experimentally as a consequence of the presence of low shunt resistances. The dark SR allows therefore to detect the presence of shunts and discriminate the defective sub-cell.
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