Comprehensive numerical analysis of doping controlled efficiency in lead-free CsSn${}_{1-x}$Ge${}_x$I${}_3$ perovskite solar cell

One effective way to prevent toxicity and improve the stability of materials for photovoltaic applications is to exclude lead and organic molecules from perovskite materials. Specifically, the CsSn${}_{1-x}$Ge${}_x$I${}_3$ appears to be a promising contender; nonetheless, it requires optimization, particularly bandgap tuning by doping concentration modifications. In this study, density functional theory (DFT) was employed to comprehensively analyze the electronic properties of CsSn${}_{1-x}$Ge${}_x$I${}_3$ that influenced light-matter interactions tuning of the perovskite materials by varying composition in B site atoms. We use the solar cell capacitance (SCAPS-1D) simulator to compute device performance; however, it computes the absorption spectrum using a simplified mathematical function that approximates the actual spectrum. To achieve a quantum-mechanical level of accuracy DFT extracted parameters like absorption spectra and bandgap were fed into SCAPS-1D. We find that increasing the Ge concentration leads to a higher bandgap and improved absorption profile, thereby enhancing solar energy conversion efficiency. Thermal and field distribution analyses were also done for the optimized device through a finite-difference time-domain (FDTD) framework. By optimizing the absorber layer with a 75% Ge concentration, we achieve a remarkable PCE of 23.55%. Our findings guide future research in designing high-performance non-leaded halide PSCs, paving the way for low-cost, stable, and highly efficient solar cells through atomic doping-tuned perovskite absorber layers.