Numerical Simulation and Optimization of a Lead-Free FTO/ZnO/BaCoCl3/Cu2O/Au Heterojunction Solar Cell Using SCAPS-1D

We report a comprehensive numerical investigation of a lead-free, inorganic heterojunction photovoltaic device based on the half-metallic ferromagnetic perovskite BaCoCl₃ as an absorber layer, sandwiched between a zinc oxide (ZnO) electron transport layer (ETL) and a cuprous oxide (Cu₂O) hole transport layer (HTL), with fluorine-doped tin oxide (FTO) as the front transparent electrode and gold (Au) as the back ohmic contact. All simulations were performed using Solar Cell Capacitance Simulator in one dimension (SCAPS-1D, version 3.3.10) under AM1.5G illumination (100 mW cm^-2) at 300 K. The baseline device (500 nm BaCoCl₃ absorber, intrinsic doping, defect density ~10¹⁶ cm^-3) yields an open-circuit voltage (V_oc) of 1.293 V, short-circuit current density (J_sc) of 12.07 mA cm^-2, fill factor (FF) of 85.14%, and power conversion efficiency (PCE) of 13.29%. Systematic optimization of absorber thickness (25–800 nm), donor doping (10¹⁰–10²² cm^-3), and bulk trap density (10¹⁰-10²² cm^-3) yields an optimized device with V_oc = 1.477 V, J_sc = 13.25 mA cm^-2, FF = 91.18%, and PCE = 17.84%, representing a 34.2% relative efficiency improvement over the baseline. The quantum efficiency (QE) spectrum confirms a sharp band-edge onset near 620 nm (~2.0 eV), consistent with the BaCoCl₃ bandgap. The effects of operating temperature (300–400 K), series resistance (R_s), shunt resistance (R_sh), and back-contact work function are systematically analyzed. The dominant loss mechanism in the baseline device is bulk Shockley–Read–Hall (SRH) recombination in the absorber, responsible for 7.67 mA cm^-2 integrated recombination current. Shunt resistance below 10³ Ω cm² catastrophically degrades performance (PCE < 4.4%). The Au back contact (work function 5.1 eV) is shown to provide near-ideal ohmic behaviour for Cu₂O. Our results demonstrate the photovoltaic potential of the novel FTO/ZnO/BaCoCl₃/Cu₂O/Au architecture as a viable inorganic, lead-free alternative to emerging perovskite solar cell technologies.

 Keywords: BaCoCl₃, lead-free perovskite, ZnO electron transport layer, Cu₂O hole transport layer, SRH recombination, heterojunction solar cell, band alignment, defect engineering.