Copper-indium-gallium-diselenide is one of the more promising thin film photovoltaic solar cell technologies. The "gold standard" for depositing the absorber layer in this photovoltaic is evaporation, and the current champion efficiency of 19.9% was achieved by vacuum evaporation of the absorber layer at NREL. Several companies are in pilot production of CIGS thin film photovoltaic solar cells using evaporation as well as sputtering, another physical vapor deposition (PVD) process.
Since both evaporation and sputtering require expensive and complex high vacuum equipment, other CIGS manufacturers are exploring non-PVD processes such as mixed oxide, mixed selenide or metal alloy nanoparticle printing. Another interesting, but less researched non-PVD process is electroplating. Controlled thicknesses of indium, copper, gallium and selenium can be sequentially be deposited onto a substrate using the respective individual plating bath, and the multilayer stack fused to form the CIGS alloy.
However, it would be ideal if the CIGS alloy could be electroplated in a single step from one plating bath containing all metals. Such alloy electroplating is relatively straight forward, if the individual metals have similar electropotentials. For example, tin and lead have similar electropotentials, and the electroplating of 60% tin and 40% lead solder alloy from one solution is routine. However, copper, indium, gallium and selenium all have varying electropotentials. While the development of a CIGS plating bath is technically possible by the proper selection of chelating/complexing agents and other chemical additives, developing the formulation chemistry to produce a stable and robust production electroplating bath presents a challenging task. The company who meets this challenge will have a winning process.