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For silicon thin-film solar cells, it is well known that one of the most important methods for preparing amorphous silicon doped with hydrogen having good stability against light-soaking degradation is by properly tuning the H2 dilution ratio in the intrinsic i-layer. However, it is difficult to improve the longevity of a Gen 5 silicon thin-film tandem module by manipulating the H2 ratio within one i-layer alone because hydrogen treatment can easily compromise the front P-layer. To solve this problem, we propose the “graded i-layer” method, which incorporates multiple i-layers with different hydrogen dilution ratios in place of the original single i-layer. By this method, a solar cell could provide higher initial power, and the degradation ratio of the module could be reduced by approximately 2%.