Non-vacuum deposition of CIGS absorber films for low-cost thin film solar cells

Thin film solar cells composed of chalcopyrite Cu(In1-xGax)(Se1-ySy)(2) (CIGSSe) absorbers have gained considerable attention in recent years in an effort to develop sustainable technologies for harnessing clean energy. Non-vacuum solution methods can reduce production costs by replacing vacuum-based deposition methods with large-scale, high-throughput processes. The efficient use of materials can reduce production costs. Non-vacuum processes generally rely on two sequential steps: solution-coating, followed by a post-annealing process. Depending on the point at which the CIGS phase evolves, non-vacuum processes can be categorized as nanoparticle (NP) approaches or molecular precursor approaches. These two types of liquid processes are believed to be compatible with a variety of applications, such as roll-to-roll coating for the production of flexible, portable devices. Additional thermal treatments using a gaseous chalcogen or oxygen can improve the absorber quality. This review describes the current status of chalcopyrite thin film solar cells fabrication methods via low-cost solution routes. An analysis of recently published reports describing liquid-based deposition methods is introduced, and the features of the development steps are compared. Finally, a discussion and future outlook are offered.