Atomic number: 52
Used in: solar cells
Criticality rating: near-critical
In 2009, solar cells made from thin films of cadmium telluride became the first to undercut bulky silicon panels in cost per watt of electricity generating capacity. That points to a cheaper future for solar power – perhaps.
Both cadmium and tellurium are mining by-products – cadmium from zinc, and tellurium from copper. Cadmium's toxicity means it is in plentiful supply: zinc producers are obliged to remove it during refining, and it has precious few other uses. “The people who manufacture cadmium telluride photocells often say one of the best things you can do with cadmium is to put it between two sheets of glass and leave it there,” says Robert Jaffe, a physicist at the Massachusetts Institute of Technology.
For tellurium, the situation is reversed. Because the global market for the element has been minute compared with that for copper – some $100 million against over $100 billion – there has been little incentive to extract it. That will change as demand grows, but better extraction methods are expected to only double the supply, which will be nowhere near enough to cover the predicted demand if the new-style solar cells take off. The US DoE anticipates a supply shortfall by 2025.
The US DoE puts a “critical” alarm on supplies of indium for the next five years, but will reduce this to “near-critical” for the period 2015 to 2025 as we get better at extracting the element or develop indium-free technologies such as conductive polymers or nanowires (New Scientist, 23 October 2010, p 40). Even so, without expanded production after 2015, the DoE says reductions in “non-clean energy demand” will be needed “to prevent shortages and price spikes”. In other words, we might need to choose which is the more important – smartphones or solar cells.