Cu(In,Ga)Se2 solar cells with improved current based on surface treated stoichiometric absorbers

Cu(In,Ga)Se2 (CIGS) solar cells based on Cu-rich instead of Cu-poor absorbers are investigated. Despite superior bulk transport properties and lower defect density, Cu-rich CIGS performances are strongly reduced due to unfavorable features at the grain boundaries and CIGS/CdS interface. A very thin (<10 nm) gallium post-deposition treatment followed by an annealing step is used to solve these issues. Such a treatment is found to efficiently passivate the grain boundaries when performed under low-selenium flux, resulting in an improved short-circuit current compared to Cu-poor references. Under higher selenium flux, the grain boundaries are no more passivated, but the CIGS/CdS interface can be strongly improved, leading to an open-circuit voltage approaching that of Cu-poor. Succession of both treatments if finally performed, improves efficiency from 7.5 to 14.4%, with higher short-circuit current (+6%) compared to Cu-poor reference. These results show that the short-circuit current of CIGS solar cells can be improved by an adequate metal-chalcogen treatment of Cu-rich absorbers, and paves the way for efficiency enhancement.