CuInGaS2

CuInS2 and its solid solution Cu(In1−xGax)S2 are copper indium sulfide chalcopyrite semiconductors. The composition Cu(In,Ga)S2 (0 ≤ x ≤ 1) is commonly used to describe a tunable absorber material where gallium substitutes for indium and adjusts the optical band gap. The material crystallizes in a tetragonal chalcopyrite structure and is typically p-type due to copper-related vacancies or antisite defects.

The electronic and optical properties are dominated by a direct band gap that can be tuned across a wide range. CuInS2 has a band gap of about 1.5 eV, while CuGaS2 reaches around 2.4 eV; intermediate compositions Cu(In,Ga)S2 allow band gaps between these values. The material exhibits strong optical absorption with coefficients exceeding 10^5 cm−1, enabling thin absorber layers. Defects, especially copper vacancies, contribute to p-type conductivity and influence carrier concentration and recombination.

Synthesis and processing techniques for Cu(In,Ga)S2 include co-evaporation or sputtering of Cu, In, and Ga followed by sulfurization or annealing in a sulfur-containing environment. Alternative scalable approaches such as chemical bath deposition or electrodeposition have been explored for forming sulfide absorber layers. Key challenges involve precise stoichiometry control, phase homogeneity, and junction quality with buffer layers, as well as managing Ga distribution to prevent phase separation and ensure uniform optical properties.

Applications of Cu(In,Ga)S2 are primarily in thin-film photovoltaics as light-absorbing layers. Its tunable band gap and strong absorption make it a candidate for CIS- and CGIS-based solar cells and related optoelectronic devices.