All-inorganic layered pseudo-halide perovskites with enhanced photovoltaic performance

Recently, two-dimensional (2D) layered halide perovskites have emerged as promising photovoltaic (PV) candidates since they are more stable and have favorable electronic properties. In the present study, we used first-principles calculations based on density functional theory (DFT) to investigate the all-inorganic 2D pseudo-halide perovskites Cs₂PbPs₂XY (Ps = SCN and SeCN and X/Y = I and Br). The 3D crystal structure of these compounds is composed of 2D perovskite layers, which serve as quantum wells for electrons and holes, and 1D spacer slabs, which form an energy barrier and trap carriers in the wells. The incorporation of a pseudo-ion reduces not only the quantum confinement but also the binding energy, which enhances the PV response. These compounds have direct band gaps in the energy range of 2.28-2.51 eV. Among the studied compounds, Cs₂Pb(SeCN)₂I₂ has a suitable band gap of 2.28 eV, a small binding energy (E _b) of 114 meV, a reduced interlayer distance (d) of 1.88 Å, and effective light absorption in the visible spectra for solar cell applications. These optical characterization outcomes represent its potential in optoelectronics, including light-emitting diodes and photo-detectors. The simulated device structure FTO/SnO₂/Cs₂Pb(SeCN)₂I₂/Spiro-MeOTAD/Cu was optimized to evaluate its PV performance. SnO₂ was used as the ETL, and Spiro-MeOTAD as the HTL. The optimal state of the device exhibited an open-circuit voltage (V _oc) of 1.91 V, a fill factor (FF) of 91.2, a short-circuit density (J _sc) of 10.2 mA cm^-2, and a power conversion efficiency (PCE) of 18.12%. This work presents a robust foundation for future studies on all-inorganic layered pseudo-halide perovskites, therefore making it possible to design improved PV devices through both theoretical and experimental approaches.