During the production of photovoltaic (PV) cells, the rough process often creates microcracks in the uncompleted cells, which then leads to the cells breaking during the fabrication process. This leads to huge losses, as much as 5-10% of all of the PV wafers are destroyed during fabrication! But now, researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL) have created an instrument that is able to sort out the wafers that won’t make it through the whole process much earlier, potentially leading to billions of dollars of savings for PV companies.
Specifically, the researchers wanted to sort out the wafers with microcracks from the ones in better condition before they went through the expensive doping processes. This newly developed instrument allows that.
The new Silicon Photovoltaic Wafer Screening System (SPWSS) is a cube-shaped furnace that is roughly 15 inches on each side and can be easily retrofitted into existing assembly lines.
It works by exposing “a silicon wafer to thermal stress in the form of carefully calibrated high temperatures,” NREL writes. “The process looks a lot like the toasting belt that turns a cold sub sandwich into a warm one. As each wafer passes through a narrow — 15-millimeter — high-intensity illumination zone, different strips of the wafer are exposed to the heat. That way, the stress travels through the wafer.”
“The temperature can be calibrated precisely — most usefully by correlating it to the thickness of the wafer, because the thinner the wafer, the less stress it can withstand. Every manufacturer has different levels at which their wafers can break from stress, so the SPWSS can be calibrated precisely via computer to meet the needs of each solar cell maker.”
Importantly, the instrument itself is very energy efficient. Thanks to a reflective cavity that is built into it, almost 100% of the energy from the power source is used. Which helps to keeps the energy costs very low, down to much less than a penny a wafer.
The researchers think that improvements such as this, in production efficiency and cost-saving technologies, are necessary in order to keep solar production in the US, rather than letting it get outsourced, as many American industries have. And it should also help to make solar power become cost competetive with other energy sources more quickly.
Source: DOE / National Renewable Energy Laboratory
Image Credits: Dennis Schroeder