Mitsubishi Heavy Industries Ltd. (MHI) has been engaged in the development of high-efficiency, large-area, thin-film silicon photovoltaic (PV) modules using Very-High-Frequency (VHF) plasma enhanced Chemical Vapor Deposition (CVD) in line with the development plan for cost down to accelerate the spread of photovoltaic modules in Japan. MHI has already developed its independent ladder-shaped electrode in amorphous Si PV module, succeeding in a large-area solar module by VHF plasma. The tandem type PV module composed of amorphous Si/microcrystalline Si is currently under development, with the tandem cell efficiency of 13.1% achieved in the test using small-area glass substrate of 5 cm². With the consignment of New Energy industrial technology Development Organization (NEDO), MHI is conducting research on the development of large-area tandem modules aiming at the conversion efficiency of 12% by reflecting the aforesaid technologies in large-area substrates.