Photon cascade engineering in AgCdF₃/Cu₂GeSiS₄ dual-absorber solar cells: from spectral complementarity to device...

This work presents a comprehensive numerical analysis of high-performance thin-film solar cells utilizing AgCdF₃ and Cu₂GeSiS₄ as absorber materials through SCAPS-1D simulations. To evaluate their photovoltaic potential, four device configurations were examined: FTO/SnS₂/AgCdF₃/Au, FTO/SnS₂/Cu₂GeSiS₄/Au, the dual-absorber structure FTO/SnS₂/AgCdF₃/Cu₂GeSiS₄/Au, and FTO/SnS₂/AgCdF₃/Cu₂GeSiS₄/SnSe/Au. A systematic optimization of critical device parameters, together with absorber thickness, acceptor concentration, and bulk defect density, was performed to maximize solar-cell performance. The optimal absorber thicknesses were found to be 800 nm for AgCdF₃ and 1100 nm for Cu₂GeSiS₄, while the corresponding acceptor concentrations and defect densities were determined to be 8.36 × 10⁷ cm^-3 and 1 × 10¹³ cm^-3 for AgCdF₃, and 1 × 10¹⁹ cm^-3 and 1 × 10¹⁴ cm^-3 for Cu₂GeSiS₄. These optimized conditions significantly suppressed Shockley-Read-Hall recombination, improved carrier mobility, and enhanced charge-collection efficiency. Among all investigated architectures, the dual-absorber device with SnSe HTL exhibited the most outstanding photovoltaic characteristics, delivering a short-circuit current density (J _SC) of 43.836 mA cm^-2, an open-circuit voltage (V _OC) of 0.819 V, a fill factor (FF) of 86.18%, and a maximum power conversion efficiency (PCE) of 30.94%. The remarkable enhancement originates from the synergistic combination of broad-spectrum light harvesting, favorable energy-band alignment, efficient charge separation, and reduced interfacial recombination losses. These findings demonstrate that integrating AgCdF₃ and Cu₂GeSiS₄ in a dual-absorber configuration offers a promising way toward next-generation, high-performance, and cost-effective thin-film photovoltaic technologies.