Systematic Optimization of Electron and Hole Transport Layers for Double Perovskite Solar Cells Using SCAPS-1D Software

Abstract Cs₂CuBiBr₆, a lead-free double perovskite of the A₂B⁺B³⁺X₆ family, has emerged as a promising absorber material for sustainable photovoltaic applications owing to its tunable bandgap (1.24–1.80 eV), intrinsic chemical stability, and environmental compatibility. This study presents a comprehensive SCAPS-1D numerical simulation of Cs₂CuBiBr₆-based solar cells, systematically screening 42 electron transport layer (ETL)/hole transport layer (HTL) combinations to identify high-performance charge-selective contacts. The simulation framework was validated against previously reported experimental data for a reference IFTO/WS₂/Cs₂CuBiBr₆/spiro-OMeTAD/Ag device, yielding a relative deviation below 7% across all key photovoltaic parameters. Multi-parameter optimization of the Al/ITO/ETL/ Cs2CuBiBr6/Cu2O Au architecture, encompassing absorber thickness, defect density, transport layer doping, series resistance, shunt resistance, and operating temperature, identifies WS₂ and PCBM as the optimal ETLs, achieving maximum power conversion efficiencies (PCE) of 22.49% and 22.44%, respectively, with open-circuit voltages of 0.83 V and short-circuit current densities of ~35.3 mA cm⁻². The superior performance of WS₂ is attributed to near-zero conduction band offset (CBO ≈ 0 eV) at the ETL/absorber interface, which suppresses interfacial Shockley–Read–Hall recombination. The reported PCE values represent theoretical upper bounds under idealized simulation conditions; practical loss mechanisms including grain boundary recombination, ion migration, and optical parasitic losses would reduce performance in fabricated devices. These results provide quantitative design guidelines for lead-free double perovskite photovoltaics and identify the optimal operating window for Cs₂CuBiBr₆-based device architectures