This study delineates an extensive numerical investigation of a dual absorber solar cell architecture integrating Cs₂BiAgI₆ and CZTS to enhance charge transport, optical absorption, and overall photovoltaic performance. Device simulations reveal that the stacked configuration generates a strong built-in potential of 1.2 V, significantly higher than that of the individual single absorber structures. This enhanced internal field promotes efficient charge separation, suppresses interfacial recombination, and enables effective carrier extraction even in a relatively thick (1000 nm + 1000 nm) absorber stack. The dual absorber device achieves a short circuit current density of 25.13 mA cm⁻², a high open circuit voltage of 1.33 V, and a power conversion efficiency of 29%. Electrochemical impedance spectroscopy further confirms the improved charge transfer characteristics, with the dual absorber cell exhibiting lower impedance than the CZTS PSC and comparable performance to the Cs₂BiAgI₆ DPSC. These results demonstrate that combining wide band gap and narrow band gap absorbers in a vertically stacked configuration offers a potentially advantageous avenue for enhanced efficiency in lead-free photovoltaic devices.
