Development of amorphous silicon/microcrystalline silicon tandem solar cells

Using very high frequency plasma CVD with a ladder-shaped electrode, manufacturing technologies for a-Si solar cells having 1.4 m/spl times/1.1 m large area glass substrate and stable efficiency of about 8% have been developed. Based on these technologies, we are currently engaged in the development of a-Si//spl mu/c-Si tandem solar cells. It was found effective to adjust the hydrogen dilution ratio so as to obtain a higher quality /spl mu/c-Si i-layer, and to deposit film under mild plasma conditions so as to optimize the p/i interface. An extremely high Voc of 0.573 V was achieved for a /spl mu/c-Si single solar cell with a /spl mu/c-SiC p-layer. The /spl mu/c-Si bottom cell features a higher quality /spl mu/c-Si i-layer and an optimized p/i interface for improved Voc, in addition to optimized fabrication processes for the back contact, delivering improved Jsc as well. As a result, initial efficiency of 13.1% has been achieved for a small area cell.