SCAPS simulation and DFT study of ultra-thin lead-free perovskite solar cells based on RbGeI3

To reduce fossil fuel usage and mitigate greenhouse effects, we have developed an ultra-thin, more stable, and environmentally friendly all-inorganic perovskite solar cell (PSC). We demonstrated the excellent stability of the perovskite absorption layer (RbGeI3) at both micro-and macroscales. The SCAPS software optimized a range of parameters, such as initial structure thickness, bandgap, and defect density, based on continuity equations, Poisson's equation, and transport equations, investigating their impact on device performance. Compared to the pre-optimized state, the optimized fill factor (FF) increased by 26%, and power conversion efficiency (PCE) improved by 34%, while the total thickness was only 700 nm, indicating lower overall stress and increased stability of the device. Additionally, we conducted density functional theory studies on RbGeI3. State density indicated a high hybridization between Ge and I atoms, aiding in forming stable chemical bonds, which was further supported by electron configuration. Charge difference density revealed charge transfer between I and Ge, enhancing the performance of PSCs. Elastic properties demonstrated that RbGeI3 not only exhibited good mechanical stability but also had good toughness, reducing stress during PSCs operation, which is crucial for long-term stability. Our study offers guidance for the development of more stable PSCs.