Materials researchers at Tallinn University of Technology have improved the efficiency of next generation photovoltaic cells by partial substitution of copper with silver in the absorber material.
A thin-film solar cell consists of several thin layers of semiconductor materials, and the TuTech researchers have been developing compound semiconductor materials named kesterites (Cu2ZnSn(Se,S)4), which in addition to excellent light absorption contain earth abundant and low cost copper, zinc, tin, sulphur and selenium. This uses a unique monograin powder technology.
"The monograin powder technology we are developing differs from other similar solar cell manufacturing technologies used in the world in terms of its method. Compared to vacuum evaporation or sputtering technologies, which are widely used to produce thin-film structures, the monograin powder technology is less expensive," said Marit Kauk-Kuusik Senior Researcher at TalTech Laboratory of Photovoltaic Materials.
The powder growth technology is the process of heating chemical components in a special chamber furnace at 750 degrees for four days, then washed and sieved in special machines, without any expensive high vacuum equipment. The synthesized high-quality microcrystalline powder, monograin powder, is used for the production of solar cells. This process technology is implemented by the Estonian-Austrian joint venture Crystalsol GmbH.
The monograin powder consists of unique microcrystals that form parallel connected miniature transparent solar cells in a large module covered with an ultra-thin buffer layer. This provides major advantages over the photovoltaic modules of the previous generation of silicon-based panels.
"We have reached the point in our development where partial replacement of copper with silver in kesterite absorber materials can increase efficiency by 2 percent. This is because copper is highly mobile in nature, causing unstable solar cell efficiency. The replacement of 1% copper with silver improved the efficiency of monograin layer solar cells from 6.6 percent to 8.7 percent," said Kauk-Kuusik. In order to commercialize the photovoltaic cells the efficiency needs to be increased to 15 percent.