Optimizing Charge Transport Layers to Enhance the Performance of Lead-Free RbGeI₃ Perovskite Solar Cells: A Comprehensive Analysis of ETL and HTL Engineering

This study investigates innovative hybrid perovskite solar cells using rubidium-germanium-iodide (RbGeI₃) as the substrate, incorporating various hole transport layers like Cu₂O, CuO, and SnSe, and wide-bandgap chalcogenide electron transport layers (ETLs) like IGZO, WS₂, In₂S₃, and ZnSe. After selecting IGZO as the optimal ETL, its depth was optimized using the SCAPS-1D simulator to evaluate device performance. Three device configurations were examined: device-I (Al/FTO/IGZO/RbGeI₃/Cu₂O/Ni), device-II (Al/FTO/IGZO/RbGeI₃/CuO/Ni), and device-III (Al/FTO/IGZO/RbGeI₃/SnSe/Ni), with a detailed analysis of the doping concentration, thickness of the layer, density of defect, operational temperature, and interface defects. Benchmarks for efficient RbGeI₃-based SCs were set, with device I achieving the highest power conversion efficiency of 33.84%, fill factor of 86.78%, open-circuit voltage (<i>V</i>_OC) of 1.13 V, and short-circuit current density (<i>J</i>_SC) of 34.54 mA/cm². Devices II and III recorded PCEs of 25.91% and 25.21%, respectively. Additionally, series-shunt resistances, generation-recombination rates, carrier dynamics, and quantum efficiency (QE %) were analyzed. Device I shows substantial potential for high-efficiency hybrid perovskite photovoltaic systems based on RbGeI₃.