Scientists in the UK have turned to an ingredient commonly used in the manufacture of tofu to dramatically raise the commercial viability of thin film solar cells.
While many have long touted the tremendous potential of cadmium-telluride-based ultra thin photovoltaic cells on the basis of their light weight and adaptability to a broad range of circumstances, the construction of the devices requires the use of cadmium chloride – an ingredient which is both toxic and costly to deploy.
A solution of cadmium chloride is used to coat the cells, greatly heightening their ability to harvest the sun’s energy by depositing a micro layer of cadmium on the surface of the finished device. This layer establishes a semiconductor junction facilitating the passage of electrons across the surface of the cell.
While this cadmium layer itself poses no harm, the usage of a cadmium chloride solution to create it has been described by scientists as “horrendous” given the highly toxic and potentially carcinogenic nature of cadmium ions while in a soluble state.
The production process is also costly, as the toxicity of the material requires the use of special protective gear by workers, and the strict filtration of waste water in order to recover any cadmium ions which may have been washed away during the coating stage.
Scientists from the University of Liverpool have discovered, however, that cadmium chloride can be replaced using an ingredient which is cheap and innocuous enough to be employed in the manufacture of food products such as soy milk and tofu.
The team of researchers, led by physicist Jon Major, scoured the periodic table for salts which could be used to make cheaper and safer coating powders, yet discovered that many of them, such as sodium chloride, failed to work because their ions interfere with the electronic structure of the devices.
They eventually discovered that magnesium chloride was an ideal fit for the production process, resulting in a cell with an efficiency level almost on par with those manufactured using cadmium chloride.
According to Major, the cells made using magnum chloride are “as good as anything we’ve ever made with cadmium chloride,” yet can be safely applied in an open environment, using an instrument as simple as an inexpensive spray coater procured online.
The chemical is extremely safe, being frequently used in Japan for the production of soya milk and tofu. It is also a mere three-hundredth the cost of cadmium chloride, retailing for around US$1 per kilo.
The discovery could bolster the prospects of the thin film solar sector, which has been hampered significantly by the rise of China as a low-cost manufacturer of photovoltaic cells.
The flooding of the market with cheap silicon cells originating from China over the past five years has taken a severe toll on thin-film manufacturers, who now find it even harder to compete with crystalline silicon in terms of cost per watt. As a consequence, cadmium-telluride cells now only have a five per cent share of the global solar market.