Lead-Free Sr₃MCl₃ (M = Sb, P) Perovskite Solar Cells: from First-Principles Calculations to Recombination-Aware...

In this study, first-principles calculations were performed to explore structural, mechanical, electronic, carrier transport, and optical properties of strontium-based perovskites (Sr₃MCl₃ (M = Sb, P)) using density functional theory (DFT). These calculations reveal that both materials are thermodynamically and mechanically stable. Employing the GGA-PBE functional, they possess a direct-band-gap semiconductor behavior with an energy of 1.704 eV (Sr₃SbCl₃) and 1.677 eV (Sr₃PCl₃). The analysis of the density of states (DOS) further corroborates the semiconducting behavior. Carrier mobility calculations indicate that electron/hole mobilities of 89.15/110.52 cm²/V·s are achieved for Sr₃SbCl₃ and 137.16/100.60 cm²/V·s for Sr₃PCl₃. In the visible region, a light absorption coefficient above 10⁵ cm^-1 is reached for both materials, highlighting their suitability as an absorber layer (AL) in perovskite solar cells (PSCs). Considering band-to-band recombination (radiative and Auger), SCAPS-1D was used to conduct an inquiry into the photovoltaic performance of various devices, integrating different electron and hole transport layers (ETL/HTL): Ag/FTO/ETL/uniform-AL/HTL/Ni. Among all configurations examined in this study, the Ag/FTO/IGZO/uniform-AL/Cu₂O/Ni architecture achieves the highest photovoltaic performance parameters, upon optimization of AL thickness, AL-doping concentration, AL-bulk and interface defect densities, radiative recombination coefficient, and series/shunt resistances. The Sr₃SbCl₃-based PSC (Device I) attains a power conversion efficiency (PCE) of ∼25.80%, with an open-circuit voltage (V _OC) of 1.31 V, a short-circuit current density (J _SC) of 21.82 mA/cm², and a fill factor (FF) of 90.27%, whereas the Sr₃PCl₃-based PSC (Device II) achieves a PCE of approximatively 26.22%, with V _OC = 1.28 V, J _SC = 22.71 mA/cm², and FF = 90.09%. Finally, replacing the single uniform-AL with a graded-Sr₃Sb_1-x P _x Cl₃ AL (Device III), adopting linear and parabolic graded physical parameters, does not demonstrate marked improvements in device performance. Consequently, this study positions Sr₃MCl₃ (M = Sb, P) perovskites as alternatives to lead-based ALs, which can constitute a suitable pathway for real-time experimentation of PSC.