Spectral characteristics of thin-film stacked-tandem solar modules

The device current-voltage (I-V) parameters of thin-film silicon stacked-tandem solar modules consisting of amorphous and microcrystalline silicon have been investigated under various spectral irradiance distributions. Spectrometric characterization method by the current mismatch perturbation has been developed using a large-area multisource solar simulator consisting of Xe lamps and halogen lamps with adequate optical filters. This method enables us to reveal the current-limited component cell and to specify the most suitable spectral distribution for tandem modules to obtain the best performance. Practical procedures for determining the irradiance level for a given single-source solar simulator have been demonstrated in order to carry out I-V measurement for tandem cells under nearly standard test conditions (STC). We have determined the differential of I-V parameters at various spectral distributions and found that the procedure using a reference tandem cell and its efficiency at STC could minimize variation from the true value even if the spectral distribution deviates from the reference.