A total area conversion efficiency of 11.1% has been achieved for a 1Ocm×1Ocm integrated-type single-junction a-Si solar cell submodule using a high-quality wide-bandgap p-layer doped with B(CH3)3 and other advanced techniques. This is the highest conversion efficiency ever reported for an a-Si solar cell with an area of 100cm2. As for a multi-junction solar cell, 12.1% was obtained for a 1cm2 cell with a high-quality wide-bandgap a-Si i-layer. The layer was fabricated by a hydrogen dilution method at a low substrate temperature for a front active layer of an a-Si/a-Si/a-SiGe stacked solar cell.
For further improvement in conversion efficiency, a wider-bandgap a-SiC was developed using a novel plasma CVD method, called the CPM (Controlled Plasma Magnetron) method. From XPS and IR measurements, the resultant films were found to have high Si-C bond density and low Si-H bond density, p-type a-SiC was fabricated using the post-doping technique, and dark conductivity more than 10-5(Q. cm)-1 was obtained (Eopt3 ≥ 2eV; Eopt2 2.2eV), whereas that of conventional p-type a-SiC is less than 10-6(Ω·cm)-1. These properties are very promising for application to the p-layers of advanced a-Si solar cells.