Lead-free hydrogenated Cs2AgBiBr6 enters perovskite/Si tandem photovoltaics: SCAPS-1D simulation-driven thickness optimization for 2T and 4T configurations

Perovskite/silicon tandem solar cells (TSCs) have progressed rapidly in recent years, achieving power conversion efficiency (PCE) surpassing the Shockley-Queisser (SQ) limit of single-junction cells. However, their development remains constrained by toxicity and stability issues in conventional organic-inorganic halide perovskites (OIHPs). Hydrogenated Cs2AgBiBr6 (HCABB), a perovskite material with enhanced stability and reduced toxicity, presents a promising solution. Nevertheless, its application in perovskite/Si TSCs remains unexplored. Utilizing an advanced single-junction HCABB PSC architecture, we modeled 2-terminal (2T) and 4-terminal (4T) perovskite/Si TSCs using SCAPS-1D, systematically investigating HCABB absorber thickness effects. After optimization, 2T and 4T configurations achieved PCEs of 24.98% (390 nm HCABB) and 24.75% (700 nm HCABB), respectively. The 4T configuration demonstrated greater thickness variation tolerance than the 2T, potentially enhancing fabrication yield. This work confirms the photovoltaic (PV) potential of HCABB in perovskite/Si TSCs and provides critical design guidelines for high-efficiency stable tandem devices.