Effective Ga incorporation for 2SSS CIGS manufacturing

Although CIGS technology has not yet demonstrated large volume commercial success, ongoing investment in manufacturing facilities is being made because of its outstanding potential. It is clearly not straightforward to transfer a high performance laboratory process to a manufacturing line. Manufacturing issues such as throughput, yield and materials utilization are not typical metrics in developing lab scale processes, and new ways of meeting these demands of the manufacturing line while keeping the lab scale performance must be found. We are developing a large area roll-to-roll piloting facility whose primary objective is to meet these demands. In support of this objective we are conducting lab-scale experiments which are guided by commercialization driven parameters. The deposition process which we favor is a 2-step process using solid Se which we designate as 2SSS. Our approach is to make side-by-side comparisons of films and devices made with this process and the ideal co-evaporation process and to demonstrate equivalent properties with a more manufacturable process. In this paper we report results on effective incorporation of Ga. We demonstrate that film properties are equivalent to those produced by co-deposition, and in particular that the processing time and use of raw materials is the same. A key finding is that selective precursor films can be configured to reduce the formation of volatile Ga x Se y species responsible for the loss of Ga and excessive use of Se.