Thin film Cu(In,Ga)(Se,S)2 (CIGSSe) solar cells exhibit conversion efficiencies that are at the same level as those based on multi-crystalline silicon wafers. Therefore CIGSSe technology has a large potential to become a significant part of the large scale production of photovoltaic energy. However, several of fabrication steps leading to CIGSSe solar modules rely on relatively slow vacuum processes and/or involve material inefficient toxic gases. This increases considerably the costs of module fabrication reducing the competitiveness of this technology. The introduction of high through-put in-line processes using non-toxic gases will lead to a significant cost reduction. Provided that the respective power conversion efficiencies can be maintained or increased, the cost of PV-generated electricity produced with this technology can be significantly reduced.

The objectives of this project were the combined reduction of CIGSSe processing cost and the improvement of the conversion efficiency. Since the CIGSSe absorber layer has the highest cost and the highest efficiency impact on the finished CIGSSe module, this project focused on improving sequential CIGSSe absorber formation by rapid thermal processing, the commercially and industrially most attractive process for the fabrication of CIGSSe absorbers. In this sequential process, stacks of Cu-In-Ga metallic films are transformed into the active absorber CIGSSe layer in a high-throughput in-line reactive thermal process by gaseous S and Se compounds. To reduce the costs involved in handling and safety measures related to toxic H2S and H2Se gases, elemental selenium (Se) and sulphur (S) vapours are used for the reaction. Furthermore, the thermal process occurs at atmospheric pressures eliminating the costs of vacuum equipment.

• Prof. Dr. Rutger Schlatmann (Projektleitung)

Bundesministerium für Wirtschaft und Energie (BMWi)