CIGS are one of the most exciting solar material

Copper indium diselenide (CuInSe₂ or "CIS") or CIGS has an extremely high absorptivity, which means that 99% of the light shining on CIS will be absorbed in the first micrometer of the material. Cells made from CIS are usually heterojunction structures—structures in which the junction is formed between semiconductors having different bandgaps. The most common material for the top or window layer in CIS devices is cadmium sulfide (CdS), although zinc is sometimes added to improve transparency. Adding small amounts of gallium to the lower absorbing CIS layer boosts its bandgap from its normal 1.0 electron-volts (eV), which improves the voltage and therefore the efficiency of the device. This particular variation is commonly called a copper indium gallium diselenide or "CIGS" PV cell.