Unraveling high-efficiency lead-free perovskite solar cells using a CsSnGeI₃/CsGeI₃ dual absorber and a Cu₂O HTL

This study examines the efficiency enhancement of lead-free perovskite solar cells using a dual absorber layer design. Through Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D), the performance of a CsSnGeI₃/CsGeI₃ heterojunction with a Cu₂O hole transport layer under AM1.5G illumination is evaluated. Key factors analyzed include absorber layer thickness, doping concentration, defect density, temperature, series resistance, and shunt resistance. The results reveal that the dual absorber design with the structure FTO/SnS₂/ CsGeI₃/CsSnGeI₃/Cu₂O/Au significantly improves the power conversion efficiency to 34.18%, achieving a short-circuit current density of 32.67 mA/cm², open-circuit voltage of 1.25 V, and fill factor of 83.64%. Each absorber layer is optimized to a thickness of 0.8 μm, leading to superior performance compared to single-layer perovskite solar cells (PSCs). The optimal doping concentrations are approximately 1 × 10¹⁷ cm⁻³ for CsGeI₃ and 1 × 10¹⁶ cm⁻³ for CsSnGeI₃, while the defect densities are minimized to about 1 × 10¹² cm⁻³ for both layers. Furthermore, maximum efficiency is achieved by optimizing additional key parameters, including an operating temperature of 300 K, and a series resistance of 0 Ωcm². This improvement stems from a broader absorption spectrum and enhanced charge separation facilitated by the heterojunction. The study provides critical insights into dual absorber configurations for advancing PSC photovoltaic performance.