In view of the need to obtain high-efficiency and low-cost photovoltaic power generation systems, the electrical series
connection of multiple solar cells by laser patterning is a key issue for thin-film silicon solar cells. For a series connection with no thermal damage to the photovoltaic layers, a theoretical analysis of glass-side laser patterning, in which a laser beam is irradiated from the side of a glass substrate, and the optimization of the structure of the solar cells are conducted for a-Si:H/a-SiGe:H stacked solar cells deposited on glass substrates. As a result, an a-Si:H/a-SiGe:H module with both a large area (8,252 cm<sup>2</sup>) and a conversion efficiency of 11.2% is obtained. Then, to improve efficiency and to reduce cost, the minute structure of microcrystalline silicon (μ c-Si:H) and film-side laser patterning, in which a laser beam is irradiated from the side of the deposited film, are investigated for a-Si:H/μ c-Si:H stacked solar
cells deposited on insulator/metal substrates. It is proved that the discontinuity of the doped and photovoltaic layer may cause a reduction in the path density of the leak current, and that this contributes to an improvement in the efficiency of the solar cells. Based on the developed structure, an initial efficiency of 12.6% is obtained in a small-size solar cell. An a-Si:H/μ c-Si:H module (Aperture area = 56.1cm<sup>2</sup>) with three segments has also been fabricated with an initial efficiency of 11.7% as a first try.