Silicon solar cell insight could help remove lead and silver from manufacturing process

The research, conducted by a team from the US Energy Department's National Renewable Energy Laboratory (NREL) and SLAC National Accelerator Laboratory, is described in a paper titled: The formation mechanism for printed silver-contacts for silicon solar cells, which appears in Nature Communications.

The paste used in the manufacturing of the solar cells contains silver powder, glass frit (a mixture of metal oxides including lead oxide, boron oxide, zinc oxide, and bismuth oxide), and an organic binder. Researchers are looking for an alternative because silver is costly and lead oxide in the glass frit can harm the environment. Before alternative materials can be chosen, however, a better understanding is needed of what takes place during the firing process.

According to NREL, the research focused on identifying the silver-contact reaction mechanism that occurs during the manufacturing of silicon-based photovoltaic cells. The process involves a silver paste screen-printed onto a silicon wafer and then fired in a belt furnace at temperatures between 750-800 degrees Celsius. The process has been used for decades in silicon solar cell manufacturing, but exactly what happens during the firing step has remained unknown because the firing process happens in seconds.