Unveiling the impact of cesium doping and functionalized carbon nanotubes on CsxFA1-xPbI3 performance: Insights from SCAPS-1D simulations

The incorporation of cesium (Cs) into formamidinium lead iodide (FAPbI₃) is widely explored to enhance the phase stability and optoelectronic properties of perovskite solar cells (PSCs). This study employs a simulation-driven optimization approach to evaluate the effects of varying Cs doping (5%, 10%, and 15%) and functionalized carbon nanotubes (f-CNTs) on the photovoltaic performance of FAPbI₃-based perovskite solar cells. Among the compositions tested, Cs_0.1FA_0.9PbI₃ (10% Cs doping) emerges as the optimal composition. It achieves the highest power conversion efficiency (PCE) owing to the ideal balance of bandgap tuning, phase stabilization, and defect passivation. In addition to compositional tuning, pristine and f-CNTs are incorporated into the Cs_0.1FA_0.9PbI₃ perovskite absorber layer (PAL) to enhance the PCE further. A comparative simulation study of pristine, carboxyl (–COOH)- functionalized, and amine (–NH₂)- functionalized CNTs shows that COOH-CNTs deliver superior charge transport properties, effectively suppress recombination losses and significantly boost efficiency. The optimized PSC configuration FTO/SnO₂/Cs_0.1FA_0.9PbI₃-COOH-CNTs/Cu:NiOx/Ag achieves an impressive PCE of 25.58%, with an open-circuit voltage (Voc) of 1.14 V, a short-circuit current density (Jsc) of 25.93 mA/cm², and a fill factor (FF) of 86.26%. These results underscore the crucial role of f-CNTs in enhancing charge separation and offer a promising route for next-generation high-performance perovskite photovoltaics.