The role of hydrogenation and gettering in enhancing the efficiency of next-generation Si solar cells: An industrial perspective

摘要

We discuss the importance of gettering and hydrogenation for next-generation silicon solar cells in the context of industrial cell fabrication. Gettering and hydrogenation play a vital role for p-type cell technologies in improving the silicon material's minority charge carrier lifetime. These mechanisms are naturally incorporated during screen-printed cell fabrication through the phosphorus emitter diffusion, silicon nitride deposition and subsequent metallisation firing processes. While the transition towards emitters with lower dopant concentrations and/or thermal oxide passivation can reduce surface recombination, it can negatively impact the ability to getter common impurities such as iron. For cell technologies with alternative low-temperature metallisation approaches, the ability to hydrogenate bulk defects is greatly reduced. Ultrahigh efficiency n-type technologies tend to use heterojunction structures rather than diffused layers, but in doing so, do not benefit from phosphorus gettering. Also, particularly for amorphous silicon-based heterojunction structures, the imposed temperature constraints strongly limit the ability to passivate bulk defects. As a result, high-efficiency n-type technologies rely on the use of 'high-quality' wafers or would require the deliberate addition of gettering and hydrogenation processes before cell fabrication. A potential high-efficiency hybrid homojunction/heterojunction structure is then discussed that could naturally enable gettering and bulk hydrogenation throughout cell fabrication. Calibrated implied open circuit voltage (V_(oc)) map of a p-type mono-crystalline wafer highlighting the impact of pre-hydrogenating the top half of the wafer.