Optimization and Simulation of CIGS Thin-Film Solar Cells Using Cd-Free Buffer Layers

In this work, we propose and evaluate four alternative buffer materials Zn₂SnO₄, ZnS, ZrSₓSe₁₋ₓ, and SnS₂ as substitutes for CdS in CIGS thin-film solar cells. The numerical simulations were performed using SCAPS-1D to study the effect of absorber (CIGS) and buffer layer thickness on the overall photovoltaic performance. The CIGS absorber thickness was varied from 1 µm to 3.5 µm, while the buffer thickness ranged between 0.01 µm and 0.06 µm. The results show that increasing the absorber thickness enhances Voc, Jsc, and η, with optimal values obtained for 3.0–3.5 µm. The influence of buffer thickness was relatively small, with the best performance achieved for 0.04–0.05 µm. Among the proposed Cd-free buffer layers, ZrSₓSe₁₋ₓ demonstrated the best performance, achieving results nearly identical to those of the conventional CdS buffer. It exhibited slightly higher Voc and comparable efficiency (η ≈ 22.4%), indicating better band alignment and interface properties.Therefore, ZrSₓSe₁₋ₓ appears to be a strong environmentally friendly alternative to CdS for high-efficiency CIGS solar cells. The optimized device structure Al/ZnO:Al/ZrSₓSe₁₋ₓ/CIGS/Mo achieved a maximum simulated efficiency of approximately 22.4%, confirming its potential for next-generation thin-film photovoltaic applications.