Midsummer AB of Jarfalla, Sweden, a supplier of production lines for manufacturing flexible copper indium gallium diselenide (CIGS) thin-film photovoltaic (PV) solar cells, has halved the thickness of its CIGS layer, to 800nm (less than half of what other suppliers can offer, it is claimed), while maintaining performance.
This lays the foundation for lower manufacturing cost, strengthening the business case for Midsummer’s CIGS solar cells, reckons CEO Sven Lindstram.
The solar cell is made on stainless-steel substrates, contains no cadmium buffer layer, and the production process is an all-dry, all-vacuum process where all layers (including the buffer layer) are deposited by sputtering, notes Lindstram.
Earlier this year, Midsummer boosted the efficiency of the whole solar cell to 16.2% for the full 156mm × 156mm aperture area. It has since raised this further, to 16.7%. Now, with the help of a new, aggressive grading of the CIGS layer, the firm has also been able to thin the CIGS layer (normally 2000nm thick) to 800nm. Most of the light is absorbed in the first 800nm, so for productivity reasons the absorber layer can be kept thin.
CIGS is the most expensive layer in the solar cell, so reducing the thickness has major cost advantages. Also, production time is reduced (increasing productivity) and it takes less energy to coat the layer, as well as reducing the time during which the substrate needs to be kept warm.
Midsummer sees the opportunity to reduce the thickness even further with a reflective back contact, i.e. any photons that have passed through the CIGS layer would be reflected and have the chance to do work on the way back.
“Our scientists are constantly working on reducing the thickness, and they will now start to work on this opportunity,” says Lindstram. “As soon as we are done, we will report it,” he adds. “We are always aiming to increase the productivity in our machines while many of our competitors are chasing records, which means their CIGS layers turn out to be thicker than ours.”
