Ba- and Mg-Doped Perovskites on Engineered TiO2 Interfaces for Efficient HTL-Free Solar Cells

<title>Abstract</title> <p> We report a synergistic material-to-device framework utilizing a low-temperature processed, amorphous TiO₂ electron transport layer (ETL) combined with cationic doping (Mg ²⁺ and Ba ²⁺ ) of the perovskite absorber. X-ray diffraction (XRD) confirms the amorphous nature of the TiO₂ scaffold, providing a pinhole-free conformal interface that suppresses shunting. UV-Vis spectroscopy reveals bandgap engineering of the perovskite upon dopant incorporation. SCAPS-1D numerical modeling demonstrates that Ba-doping can yield a predicted short-circuit current density (J _SC ) of ~ 23.6 mA/cm², while Mg-doping optimizes the open-circuit voltage (V _OC ) to ~ 1.16 V. Simulations reveal that enhanced performance is primarily driven by a substantial reduction in bulk defect density (Nt), decreasing from 5 × 10¹⁶ cm⁻³ in the pristine device to 8 × 10¹⁴ cm⁻³ in the doped variants. The amorphous ETL facilitates high shunt resistance, while cation engineering effectively passivates interfacial traps, resulting in reduced hysteresis. These findings provide a computational framework for optimizing HTL-free heterojunction PSCs through combined structural engineering and electronic defect reduction. </p>