CopperIndiumGalliumDiselenid

Copper indium gallium selenide, commonly abbreviated as CIGS, is a quaternary compound semiconductor used as an absorber material in thin-film solar cells. The composition Cu(In1−xGax)Se2 forms a continuous solid solution between CuInSe2 (x = 0) and CuGaSe2 (x = 1). By varying x, the material’s bandgap can be tuned from about 1.0 eV to 1.7 eV, enabling optimization of the solar spectrum response for different device architectures.

The crystal structure of CIGS is chalcopyrite, and thin films of the material can achieve strong light absorption with thicknesses of a few micrometers. Typical CIGS solar cells include a molybdenum back contact, the CIGS absorber, a buffer layer (historically CdS, but increasingly Cd-free options such as Zn(O,S) or In2S3), and a transparent conducting oxide like ZnO or ITO as the front contact. The devices are often built on glass or flexible substrates, enabling large-area processing.

Manufacturing methods for CIGS devices include co-evaporation, sputtering followed by selenization or sulfurization, and various electrodeposition approaches. The technology benefits from high absorption coefficients, enabling high efficiencies with relatively thin absorbers, and from compatibility with flexible and large-area production.

Advantages include strong absorption, a tunable bandgap, and potential for high efficiencies on flexible substrates at comparatively low processing temperatures. Challenges involve precise control of Ga distribution, sodium-related effects from substrates, and environmental and supply-chain considerations associated with indium, gallium, and, in some buffer configurations, cadmium. Ongoing research targets Cd-free buffers, interface optimization, and scalable manufacturing to improve module performance and stability.