Solar brilliance unleashed: Maximizing performance of novel carbon-based Rb-doped CsSnI3 perovskite solar cells by gradient doping

The commercialization of state-of-the-art perovskite solar cells (PSCs) is hindered by lead toxicity, high production costs, and stability issues. The current study addresses these challenges by exploring lead-free Rb-doped CsSnI₃ perovskite with carbon-based materials. Herein, the impact of Rb-doping in CsSnI₃ perovskite has been thoroughly investigated on its structural, electrical, and optical properties via DFT studies. The results show that the incorporation of Rb-cation into CsSnI₃ significantly enhances the stability of the perovskite active layer (PAL), addressing the major challenge of degradation under environmental conditions. Further, DFT results are used to investigate the potential of Cs_0.75Rb_0.25SnI₃ as a PAL in device architecture FTO/ETL/Cs_0.75Rb_0.25SnI₃/CNTs/C via SCAPS-1D with different electron transport layer (ETL) and carbon-based hole transport layer and back contact. Simulation results show that among different ETLs, WO₃ demonstrates the best performance. Further, we have employed a gradient doping (GD) strategy in PAL, dividing it into two sub-layers of thickness 200 nm each with different doping concentrations in the simulated device FTO/WO₃/CsRbSnI₃/CNTs/C. The aim of implementing GD is to strengthen the electric field and improve the energy band alignments which helps in reducing interfacial recombination. Besides, the impact of band-gap, interfacial defects, hysteresis effect, and C–V and C–F analysis are examined. The results reveal that at doping gradient G = 300, the device attains the best PCE of 19.05% with E_g of 1.32 eV (PAL-1) and 1.22 eV (PAL-2). This study can serve as a benchmark for developing high-performance and low-cost CsRbSnI₃-based PSCs utilizing a gradient doping strategy.