The Impact of Ag Substitution on the Structural and Optoelectronic Properties of Cu₂ZnSnS₄ and Cu₂CdSnS₄ for Photovoltaic Applications

The pursuit of eco-friendly and cost-effective photovoltaic (PV) technologies has driven significant interest in high-bandgap thin-film solar cells, such as kesterite, chalcopyrite, and perovskite materials [1]. Among them, Cu₂ZnSnS₄ (CZTS) stands out as a highly promising candidate due to its composition of Earth-abundant, non-toxic elements. CZTS combines an optimal bandgap with a high absorption coefficient, offering excellent optical and electronic properties that are ideal for single-junction and tandem solar cell applications [1]. Cu₂CdSnS₄ has emerged as a promising thin-film solar cell material, demonstrating excellent photovoltaic potential and device efficiency [2]. Cation substitution, particularly with Ag and Cd, is an effective strategy for enhancing Cu₂ZnSnS₄ solar cell performance. Ag reduces the open-circuit voltage deficit and defect density, and Ag substitution in Cu₂ZnSnS₄ reduces the open-circuit voltage deficit by limiting radiative and non-radiative recombination [2]. In this study, we investigate the structural, electronic, and optical properties of Ag-doped Cu₂ZnSnS₄ and Cu₂CdSnS₄ using density functional theory with a hybrid functional approach. Our primary objective is to understand how Ag substitution influences the lattice geometry, electronic bandgap, and optical absorption characteristics of these chalcogenide compounds. To gain deeper insights into the doping mechanisms, we analyze the electronic structure through the density of states (DOSs), partial DOSs (PDOSs), and electron density difference maps. Additionally, device-level simulations are conducted to assess the photovoltaic performance of Ag-doped materials, further evaluating their potential as efficient absorber layers in thin-film solar cells.

References

[1] A. Wang et al. Sustain. Energy Fuels 2021, 5, 1044−1058

[2] A Ibrahim, et al, Mater. Chem. A, 2024, 12, 2673