Plasmonically Engineered All-Inorganic Lead-Free Tin-Doped High Performance Perovskite Solar Cells

Lead-free all-inorganic perovskite solar cells are gaining significant attention owing to their improved operational stability and nontoxicity. One such promising perovskite material is CsGeCl3; however, its high bandgap renders it unsuitable for use in single-junction perovskite solar cells (PSCs). This study employs first-principles density functional theory (DFT) calculations to explore the effects of tin (Sn) doping to reduce the bandgap and consequently enhance optical performance. Incorporation of 67% Sn atoms with 33% germanium (Ge), a bandgap of 1.58 eV was observed, making it suitable for a single-junction PSC. The absorption coefficient, complex refractive index, and band structures of both pristine and doped perovskite absorbers have been analyzed. Subsequently, an all-inorganic PSC with the optimized absorber layer (CsSn0.67Ge0.33Cl3) was designed to evaluate the device’s performance. Optical simulations were employed through the finite-difference time-domain (FDTD) technique. To further enhance performance, a hole transport layer (HTL) grating with a thin plasmonic metal over-layer was incorporated. Various structural parameters of the grating were adjusted, and different plasmonic metals were tested for the thin layer. The highest short-circuit current density (JSC) was achieved with aluminum (Al). The optimized nanograting PSC yielded a JSCof 28.14 mA/cm2compared to 23.63 mA/cm2for bare CsSn0.67Ge0.33Cl3PSC, and a power conversion efficiency (PCE) of 30.07% in comparison to 25.32% for bare CsSn0.67Ge0.33Cl3PSC resulting in a 18.75% increase in PCE. This computational study underscores the potential of bandgap engineering and optical manipulation using nanogratings to enhance the optical performance of stable and environmentally sustainable PSCs.