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Solar Cell Manufacturing Advance: Expensive, Toxic Metal Replaced By Cheap Food Additive

by on July 1, 2014

A group of condensed matter experimental and theoretical physicists from the University of Liverpool has formulated a new method of manufacturing solar cells which replaces an extremely toxic and expensive chemical, cadmium chloride (CdCl2), with an edible and very cheap one, magnesium chloride (MgCl2).  The switch has no effect on efficiency of the solar cells and moreover is simple to implement by a quick substitution of salts in current manufacturing processes.

Solar cell usage grew by 76% in 2012, helped by improving technology and the entrant of low cost manufacturers from China.  Crucial to the manufacturing of solar cells is the doping of the important cadmium telluride substrate with CdCl2 to form the photovoltaic junction with cadmium sulfate.  Without CdCl2 doping, the efficiency of the cell is about 2%, but with the dopant it shoots up to 20%.

The great drawback of using CdCl2 is that it is comparatively expensive at 30 cents per gram, and moreover, highly toxic.  It is a known irritant that causes shortness of breath, chest pain, edema, liver and kidney damage.  It is also a chronic toxicant, such that long term exposure leads bone softening, increased blood pressure, kidney damage.  Finally it is a carcinogen, able to damage DNA, proximity to it being a known cancer risk.

It is also costly as a salt, at 30 cents per gram the total cost for a Gigawatt of power production is about $1.5 million.  But by far the greatest cost comes from building the capacity to acquire, handle and dispose of the chemical safely.

Professor Ken Durose who led the research.

Professor Ken Durose who led the research.

The Liverpool group led by Professor Ken Durose found that simple substitution with MgCl2 in one swoop was able to duplicate all of the benefits of CdCl2 and at once lowering the cost to less than 1 cent per gram.  The MgCl2 compound is also very safe, used in food preparation such as for coagulation of tofus, and in treating wintry roads such as for deicing.

The researchers say that the two metal salts can be simply exchanged in the manufacturing process.  The only difference being that the handling of the MgCl2 is much simpler and cheaper to carry out.

The solution is not a perfect match though.  At high voltages the maximum current density is less than that of CdCl2 though at lower voltages the two correlate much closer.  The authors proceeded also to show that substitution with other metal salts such as table salt (NaCl) and potassium chloride (KCl) was overall less efficient than MgCl2.

The research was published in Nature.

*Nature (2014) doi:10.1038/nature13435

(Photo Credit: Johan Douma / Creative Commons)


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