Cu(In, Ga)Se2 solar cells with improved current based on surface treated stoichiometric absorbers. Issue 1 (26th September 2016) - Choubrac, Léo
Abstract : 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.