Optimization of CZTS Absorber Layer for Enhanced Efficiency in CZTS/CIGS Tandem Solar Cells: A Comprehensive Loss Analysis

This study numerically optimizes Cu2ZnSnS4 (CZTS)/Cu(In,Ga)Se2 (CIGS) tandem solar cells (TSCs) with a ZnS buffer layer using Silvaco-Atlas software, achieving a record simulated efficiency of 29.41% (AM1.5G), a 4.14% improvement over the baseline (25.27%). Critical loss mechanisms are addressed through systematic parameter optimization: a CZTS absorber thickness of 0.18 µm balances photon absorption and transmission, while a doping density of 3×1016 cm-3 minimizes recombination losses by optimizing the depletion width. Comprehensive loss analysis reveals that excessive CZTS thickness (> 0.18 µm) obstructs low-energy photons from reaching the CIGS subcell, while overdoping (> 3×1016 cm-3) narrows the depletion region, elevating recombination. Temperature-dependent simulations (260 – 380 K) demonstrate a 12.83% efficiency decline at 380 K, driven by bandgap narrowing (Varshni’s Effect) and increased recombination. This work resolves critical challenges in optical losses and thermal instability, providing a roadmap for eco-friendly, high-efficiency tandem photovoltaics.