Enhanced Photovoltaic Performance in Cs-Rb Dual-Absorber Solar Cells via Synergistic Band Engineering and 2D Buffer Optimization

Lead-free and environmentally robust perovskite solar cells (PSCs) have emerged as a promising pathway for next-generation photovoltaic technologies. In this study, high-efficiency single- and dual-absorber PSC structures are designed and numerically investigated using Cs₂AgInBr₆ and RbPbBr₃ as complementary absorber materials, incorporating a two-dimensional buffer layer within the SCAPS-1D simulation framework. Two device architectures are examined: Device I (ITO/WS₂/Cs₂AgInBr₆/Pt) and Device II (ITO/WS₂/Cs₂AgInBr₆/RbPbBr₃/Pt). The introduction of the RbPbBr₃ secondary absorber in Device II significantly expands the optical absorption range and enhances charge transport through favorable energy band alignment. Comprehensive optimization of key parameters—including absorber thickness, acceptor concentration, defect density, and operating temperature—demonstrates that device performance is strongly influenced by recombination mechanisms and interfacial transport barriers. The dual-absorber Device II achieves outstanding power conversion efficiency (PCE) of 33.17%, with short-circuit current density (J_SC) of 34.784 mA/cm², open-circuit voltage (V_OC) of 1.104 V, and a fill factor (FF) of 86.36%, surpassing the single-absorber Device I, which achieves PCE of 28.24%. This enhanced performance is attributed to suppressed recombination, more efficient carrier extraction, and improved quantum efficiency across a wide spectral window (350–900 nm). The findings of this study provide valuable insights for PSC optimization and offer a foundation for future experimental and theoretical efforts focused on enhancing device stability, interface engineering, and material development.