CdTe

Cadmium telluride (CdTe) is a binary II-VI semiconductor with a direct bandgap of about 1.45 eV, near the optimum for absorbing sunlight. Its high optical absorption coefficient allows the construction of thin absorber layers, typically a few micrometers thick, which enables lightweight and large-area devices. Crystallographically, CdTe commonly forms a zinc blende (cubic) structure in thin films, though polycrystalline and textured forms are used in devices.

CdTe is produced as both bulk crystals for detectors and as thin-film polycrystalline films for photovoltaics. In solar cells, CdTe is deployed as the absorber layer in a heterojunction with a cadmium sulfide (CdS) window layer, on suitable substrates. Post-deposition treatments, such as CdCl2 annealing, promote grain growth and improve carrier transport. Common thin-film deposition methods include close-spaced sublimation, sputtering, vapor transport, and electrochemical deposition.

The principal applications of CdTe are in solar photovoltaics and radiation detection. CdTe-based solar cells and modules have achieved high efficiency in laboratory settings and are commercially deployed, with major production from companies developing large-area thin-film modules. CdTe detectors are valued for high atomic numbers (Cd and Te) that yield good gamma and x-ray absorption, making them suitable for medical imaging, security, and industrial radiography.

Advantages of CdTe technology include strong light absorption, potential for low-cost, scalable manufacturing, and good long-term stability under outdoor conditions. Limitations involve the toxicity of cadmium, the relatively long-term availability of tellurium, and environmental and recycling concerns associated with cadmium-containing devices. Ongoing research aims to optimize efficiency, reduce material use, and enhance end-of-life recycling for CdTe products.