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

Abstract 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,