Cadmium telluride photovoltaics

[1] Cadmium telluride PV is the only thin film technology with lower costs than conventional solar cells made of crystalline silicon in multi-kilowatt systems.

[1][2][3] On a lifecycle basis, CdTe PV has the smallest carbon footprint, lowest water use and shortest energy payback time of any current photovoltaic technology.

[11][12] The usage of rare materials may also become a limiting factor to the industrial scalability of CdTe technology in the mid-term future.

The abundance of tellurium—of which telluride is the anionic form—is comparable to that of platinum in the Earth's crust and contributes significantly to the module's cost.

With a share of 5.1% of worldwide PV production, CdTe technology accounted for more than half of the thin film market in 2013.

However, this technology suffers from low efficiencies and slow deposition rates (leading to high capital costs).

The latter is beginning to be produced in volumes of 1–30 megawatts per year due to very high small-area cell efficiencies approaching 20% in the laboratory.

[17] Research in CdTe dates back to the 1950s,[18][19][20][21][22][23] because its band gap (~1.5 eV) is almost a perfect match to the distribution of photons in the solar spectrum in terms of conversion to electricity.

A simple heterojunction design evolved in which p-type CdTe was matched with n-type cadmium sulfide (CdS).

[27] An important step forward occurred when cells were scaled-up in size to make larger area products called modules.

CdTe cells achieved above 15% efficiency in 1992 by adding a buffer layer to the TCO/CdS/CdTe stack and then thinned the CdS to admit more light.

[27] Golden Photon held the record for a short period for the best CdTe module measured at NREL at 7.7% using a spray deposition technique.

[28] Antec was able to make about 7%-efficient modules, but went bankrupt when it started producing commercially during a short, sharp market downturn in 2002.

Then, the Cd and Te2 gases flow across a cooler downstream region where they condense on a substrate to form solid CdTe.

CdS is source of inefficient absorption, while MZO has a tunable band gap that can be optimized for high transparency and good alignment with CdSexTe1−x.

CdTe PV modules provide a beneficial and safe use for cadmium that would otherwise be stored for future use or disposed of in landfills as hazardous waste.

A large growth in the CdTe PV sector has the potential to reduce global cadmium emissions by displacing coal and oil power generation.

Te is almost exclusively obtained as a by-product of copper refining, with smaller amounts from lead and gold production.

[57] One gigawatt (GW) of CdTe PV modules would require about 93 metric tons (at current efficiencies and thicknesses).

Cadmium chloride is toxic, relatively expensive and highly soluble in water, posing a potential environmental threat during manufacture.

It is often assumed that the open-circuit voltage gap seen in CdTe, in comparison to both single-crystal GaAs and the theoretical limit, may be in some way attributable to the grain boundaries within the material.

There have however been a number of studies which have suggested not only that GBs are not deleterious to performance but may in fact be beneficial as sources of enhanced carrier collection.

So, the exact role of the grain boundaries in limitation of performance of CdTe-based solar cells remains unclear and the research is ongoing to address this question.

[73] Materials that can be recovered in the recycling process include metals, mounts, glass, and, in high value cases, the whole PV module.

[76] Due to the exponential growth of photovoltaics the number of worldwide installed PV systems has increased significantly.

These reductions show a highly beneficial change in the overall environmental profile of CdTe photovoltaic module.

The LCA also showed that the main contributors to considered environmental impact categories are due to required chemicals and energy within the processing of CdTe modules.

[81] When inhaled or ingested the materials of CdTe cells are considered to be both toxic and carcinogenic by the US Occupational Safety and Health Administration.

Despite the small amounts of Cd that may leach out, CdTe modules have low overall leachability as the hazardous materials within them are encased within two layers of glass.

[83] Utility-scale CdTe PV solutions were claimed to be able to compete with peaking fossil fuel generation sources depending on irradiance levels, interest rates and other factors such as development costs.