Optimization of multiple ETL and HTL layers for high-performance lead-free CsSnGeI₃-based perovskite solar cells: a simulation study

Lead-based perovskite solar cells (PSCs) offer high efficiencies but pose environmental and stability challenges due to lead toxicity. Cesium tin-germanium tri-iodide (CsSnGeI₃) emerges as a promising lead-free absorber, combining favorable band alignment and improved stability. In this work, we use SCAPS‑1D solar cell simulator to systematically optimize CsSnGeI₃-based PSCs by varying multiple electron transport layers (ETLs: PCBM, ZnO, TiO₂) and hole transport layers (HTLs: PTAA, NiO, PEDOT: PSS). Each device (ITO/ETLs/CsSnGeI₃/HTLs/Au) is illuminated under standard AM1.5G (1000 W/m²) conditions, and key photovoltaic parameters- short-circuit current density (J SC ), open-circuit voltage (V OC ), fill factor (FF), and power conversion efficiency (PCE) are observed. Our simulations reveal that inorganic transport layers yield superior performance: notably, the device structure ITO/ZnO/CsSnGeI₃/NiO/Au achieves the highest simulated PCE of 32.41%, with J SC of 28.38 mA/cm², V OC of 1.35 V, and FF of 84.54%. These findings highlight optimized architectures for lead-free CsSnGeI₃ PSCs, guiding experimental efforts toward high-efficiency, stable devices.