RbF-PDT induced sodium displacement in Cu(In, Ga)Se2 absorbers grown under high substrate temperatures

Alkali metals play a crucial role in the performance and growth of polycrystalline CIGSe solar cells. Here solar cells are investigated, that were grown in a high substrate temperature co-evaporation process with a focus on the depth distribution of Na at very high process temperatures. Devices with and without RbF post deposition treatment are characterized with the goal of understanding how the two alkali metals interact. It can be shown that at high process temperatures only very little Na is present in the films and located only at the absorber surface. After a RbF-PDT even the superficial Na disappears in all finished devices. The strong influence of the temperature on the Na content in the films needs to be accounted for and optimized for high efficiency solar cells grown above 600°C.