Optical second-harmonic generation in hydrogenated amorphous silicon single- and double-junction solar cells

Using an electric-field-induced optical second-harmonic generation (EFISHG) technique, we studied the SHG from hydrogenated amorphous silicon (a-Si:H) solar cells. The SHG signal originating from a-Si interface is independent of external bias voltage (V _ex), whereas that generated from the intrinsic layer is strongly dependent on V _ex. The difference in the tendency of bias-dependent EFISHG intensity between a-Si singlejunction solar cells and a-Si/microcrystalline silicon (μc-Si) double-junction (tandem) solar cells indicates the presence of another origin of the EFISHG generation in the tandem cells. That is, the p-n junction formed between the p-type μc-Si:H and n-type a-Si:H. These findings indicate that the EFISHG technique is available for characterizing the local electric field in a-Si solar cells.