Engineering news
Researchers from the University of Liverpool have developed a cheaper and safer manufacturing process for solar photovoltaic cells that uses the same substance used in the production of tofu, road deicers and bath salts.
The process replaces cadmium chloride, a highly toxic and expenive substance, with magnesium chloride, a cheap and abundant salt which is extracted from seawater. Cadmium chloride is used to boost the efficiency of thin-film photovoltiac (PV) solar cells from 2% to over 15%. The chemical, which is difficult to manufacture and handle, is coated onto the cells during a complex step in the manufacturing process.
But researchers at the University of Liverpool have found that the chemical can be substituted for magnesium chloride to enable cheaper and safer manufacturing of thin-film PV solar cells.
The discovery is a boost for ultra-thin photovoltaics, particularly those based on cadmium telluride. Despite using less material and offering the opportunity to use flexible backings, the use of cadmium telluride PV cells has not increased because of the reduction in cost of silicon cells in recent years.
Dr Jon Major, a physicist at the University of Liverpool's Stephenson Institute for Renewable Energy, said: “We hope that this discovery can make a significant impact on the cost and safety of solar power production. It's low cost and non-toxic, vital attributes for a renewable energy technology.”
The first step in the process uses a sputtering deposition system to put a layer of cadmium suplphide onto normal window glass. A close space sublimination system is then used to deposit the cadmium telluride layer. This is the layer that absorbs sunlight.
In a conventional process the next step would be to place cadmium chloride onto the cell structure. Whereas cadmium chloride requires elaborate safety measures to protect workers during manufacture, and specialist disposal when the panels are no longer needed, magnesium chloride can be applied to the cells using a spray gun bought from a model shop.
During the final steps in the manufacturing process, the cell is placed in a furnace to be annealed and the contacts are put onto the cell.
According to the researchers, magnesium chloride costs $0.001 per gram compared to $0.3 per gram for cadmium chloride. Major said: “If renewable energy is going to compete with fossil fuels, then the cost has to come down. Great strides have already been made, but the findings in this paper have the potential to reduce costs further.”