Introduction of the distribution of Cs in Cu(In,Ga)Se2 photovoltaic absorbers following post-deposition treatment with CsF

In recent years, the device performance of Cu(In,Ga)Se2 (CIGS) solar cells has been improved by heavy alkali element post-deposition treatment (Alkali-PDT). Therefore, it is of great significance to study the mechanism of enhancing CIGS device performance through Alkali-PDT. One aspect to be studied is the distribution of heavy alkali elements in the absorber. In this work, the distribution of the heavy alkali element Cs in the absorber after post deposition treatment of CsF (CsF-PDT) and its effect on the device performance are investigated. The experimental results indicate that Cs can enter both the grain interior (GI) and grain boundaries (GB) via the Cu vacancy (V Cu ). By comparing the distribution of Na and Cs in the film, it can be noticed that Na is mainly distributed at the GB, while Cs is not differently distributed between the GB and GI. This is mainly due to the fact that the presence of Na at GB inhibits the accumulation of Cs there. The distribution of Cs is beneficial in improving the device’s performance by passivating defects, such as In Cu .