Development of amorphous silicon-germanium and nanocrystalline silicon based multi-junction solar cell technology for GW-scale manufacturing

Though thin film silicon has evolved into an important technology for photovoltaic industry, further increasing its conversion efficiency remains to be a key task. In this work, we report the progress we have made in developing compatible nanocrystalline Si (nc-Si) technology with our existing amorphous silicon germanium (a-SiGe) based multi-junction solar cell manufacturing lines. We have conducted experiments mainly on two types of nc-Si based solar cell structures, a-Si/a-SiGe/nc-Si triple-junction and a-Si/nc-Si double-junction device. Currently we are attaining initial total area efficiency of 10.7% and 12.4% for the triple- and double-junction structures, respectively, on substrate size of 0.79 m² (1.245 m × 0.635 m). Experimental results including study of crystalline volume fraction along nc-Si growth, individual component cell optimization and current match, development of superior tunnel-junction and contact layers are presented.