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Cadmium Telluride

Like silicon, cadmium telluride (CdTe) is a crystal. When brought into close contact with cadmium sulfide, the p-n junction needed for a photovoltaic panel to operate is created. CdTe accounts for 6% of all solar panels produced in the world. CdTe comes in a polycrystalline form in most cases, though it is possible to create nanocrystals for use in flexible applications, just as with silicon.

CdTe research began in the 1950s as a result of the understanding of “band gaps.”  A band gap is the amount of energy needed to eject a “loose” electron from an atom so that it can become mobile and participate in electrical phenomena. For CdTe, the band gap is almost exactly the same as the energy in photos from the solar spectrum. In other words, CdTe easily makes electricity when exposed to sunlight.

Cadmium is a relatively rare element and also toxic. Inhalation of cadmium can cause pulmonary edema and death. However, solar panels and batteries are generally not a source of aerosolized cadmium. Rather, cigarette smoke and fossil fuel burning are the major contributors to atmospheric cadmium. Leaking of cadmium into ground water can cause it to build up in plants downstream. This is potentially dangerous if humans consume the plants. The elevated levels of ingested cadmium can lead to kidney damage.

Tellurium is only mildly toxic. However, it is one of the rarest elements in the Earth’s crust with an occurrence similar to that of platinum. Currently there is little demand for tellurium, so it is relatively inexpensive. A substantial increase in the use of CdTe photovoltaic panels would drive up the cost of this element and make CdTe panels much more expensive and probably not competitive with silicon.

CdTe Photovoltaic panels

Solar panels made from CdTe have the advantage of being substantially cheaper than those made from silicon. This results at least partially from the fact that silicon is in much higher demand than either cadmium or tellurium. The largest use of cadmium is in nickel-cadmium rechargeable batteries. Approximately 86% of all cadmium is used for batteries.

In 1992, the efficiency of CdTe panels rose above 15%. This development was necessary to make these panels competitive with other forms of photovoltaic panels. Currently the best efficiency that can be achieved is 16.5%. There are rumors that these panels could reach 20% efficiency, but this is still far behind the current 40% achieved by silicon panels in laboratory settings. For the average consume PV panel, CdTe is about 11% efficient and silicon is 13% to 20% efficient. This means that more CdTe panels are needed to achieve the same power supply as fewer silicon panels. The result is somewhat increased price that reduces the cost benefit that CdTe panels enjoy.
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