Comprehensive TCAD study of two-terminal MAPbI 3 /Sb 2 Se 3 tandem solar cells: HTL architecture, ETL engineering, and defect-tolerance analysis achieving 27.31% efficiency

Two-terminal (2-T) perovskite (MAPbI₃)/Sb₂Se₃ monolithic tandem solar cells are investigated via Silvaco Atlas TCAD simulations under AM1.5G illumination. Four architectures, combining NiO or PTAA and Spiro-OMeTAD or PEDOT:PSS hole-transport layers (HTLs), are optimized for absorber thickness, doping, and C₆₀ electron-transport layer (ETL) geometry and doping, using sub-cells calibrated against experimental data. The NiO/Spiro-OMeTAD architecture is superior, reaching a peak power conversion efficiency (PCE) of 27.31% (Jsc = 15.15 mA cm⁻², Voc = 2.0485 V, FF = 88%), to our knowledge the highest reported for MAPbI₃/Sb₂Se₃ in a 2-T TCAD study with conventional organic HTLs. Optimal absorber thicknesses are 200 nm each, with Sb₂Se₃ remaining current-limiting; thinning the C₆₀ ETL to 10-20 nm and doping it to 10¹⁹ cm⁻³ reduces parasitic absorption and improves FF by 6.4 percentage points via ohmic contacts. PCE stays above 97% of its peak up to perovskite doping of 10¹⁶ cm⁻³. Defectdensity mapping shows series resistance follows a sub-linear power law (α ≈ 0.45) and shunt resistance a percolation-like threshold (β ≈ 19), giving a theoretical ceiling of 29.45% with both sub-cells' defects minimized. Over 25-85 °C, PCE falls at -0.266%/°C, matching state-of-the-art perovskite tandems. These results offer quantitative design guidelines for efficient, low-cost perovskite/Sb₂Se₃ tandem photovoltaics.