Optimization of CZTS absorber layer for enhanced efficiency in CZTS/CIGS tandem solar cells: A comprehensive loss analysis

Abstract This study numerically optimizes Cu 2 ZnSnS 4 (CZTS)/Cu(In,Ga)Se 2 (CIGS) tandem solar cells (TSCs) with a ZnS buffer layer using Silvaco-Atlas software, achieving a record simulated efficiency of 29.41% (AM1.5 G), 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 × 10 16 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 × 10 16 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.