Performance Impact of Lead-Free CsSn0.5Ge0.5I3 Based Perovskite Solar Cells with HTL-Free Incorporation

Lead-containing halide perovskites show promise for solar energy but pose ecological and health risks. To address these, researchers are exploring inorganic binary metal perovskites. This study proposes an eco-friendly, durable hole transport layer (HTL)-free design of CsSn_0.5Ge_0.5I₃ with high power conversion efficiency (PCE). Using the SCAPS-1D simulator, we assessed the efficiency of an HTL-free planar heterojunction, while the Density Functional Theory (DFT)-based CASTEP simulator evaluated the optical properties of CsSn_0.5Ge_0.5I₃ in an orthorhombic structure. Key findings highlight enhanced performance under 100 Wm⁻² AM 1.5G illumination by optimizing absorber layer thickness to 800 nm and reducing defect densities in both the perovskite absorber layer and interfaces to 1 × 10¹⁴ cm⁻³.Additonally, the effects of different electron transport materials (ETMs), optimization of electron transport layer (ETL) thickness (30-50 nm), and back contact design improvements were examined. The simulation's results included an increase over the highest values reported in the literature: an open circuit voltage (Voc) of 1.06 V, a short circuit current density (Jsc) of 28.52 mA/cm², a fill factor (FF) of 86.57%, and a PCE of 26.18% for the FTO/Zn_0.875Mg_0.125O/CsSn_0.5Ge_0.5I₃/Se perovskite solar cell (PSC). This research provides theoretical insights for developing high-efficiency power modules without HTLs with significant industrial and research potential.