Performance Impact of Lead-Free CsSnGeI 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 CsSnGeI 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 CsSnGeI in an orthorhombic structure. Key findings highlight enhanced performance under 100 Wm 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 × 10 cm.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/cm, a fill factor (FF) of 86.57%, and a PCE of 26.18% for the FTO/ZnMgO/CsSnGeI/Se perovskite solar cell (PSC). This research provides theoretical insights for developing high-efficiency power modules without HTLs with significant industrial and research potential.