Absorber-Doping Electrical Trade-off and MgF 2 Optical Enhancement in CIGS/In 2 S 3 Thin-Film Solar Cells: A TCAD Analysis

Abstract

Thin-film Cu(In,Ga)Se2 (CIGS) solar cells with a non-toxic In 2 S 3 buffer are a credible alternative to CdS-based devices. This work investigates an Al-Ni/MgF₂/ZnO:Al/i-ZnO/In₂S₃/CIGS/Mo solar-cell architecture using Silvaco ATLAS, with particular emphasis on the influence of CIGS absorber acceptor concentration (N A , 1×10 14 –1×10 17 cm -3 ) on J sc , V oc , FF, η, and the apparent series (R s ) and shunt (R sh ) resistances, with and without an MgF₂ antireflection coating. V oc rises almost monotonically with N A (+32%) while J sc falls (−6.6%), so the pronounced non-monotonic evolution of FF primarily determines the location of the efficiency maximum. The highest simulated efficiency occurs at N A = 3×10 16 cm -3 (η = 23.65% with MgF 2 versus 20.99% without), but this maximum sits inside a fairly flat doping window (1×10 16 -6×10 16 cm -3 , η ≥ 95% of the peak) rather than a single sharp optimum. The resulting data reveal a strong association between the FF collapse and the increase in apparent R s (r ≈ −0.99 overall, ≈ −0.999 above 3×10 16 cm -3 ), linking the efficiency roll-off to degraded resistive transport without proving a single cause. The MgF 2 layer delivers a nearly constant J sc gain (12.16%), a marginal V oc effect (0.4-0.5%), and a negligible FF effect, so its efficiency gain (12.3-12.8%) is almost entirely inherited from J sc . Together, these results distinguish the electrical trade-off associated with absorber doping from the predominantly optical contribution of MgF₂ and provide a practical doping window for CIGS/In₂S₃ device design.