In this work, a lead-free, high-efficiency device structure design, FTO/ \(\hbox {WS}_2\) / \(\hbox {MgHfS}_3\) / \(\hbox {Cs}_2\hbox {PtI}_6\) /Spiro-OMeTAD, termed transition-chalcogenide-based multijunction architecture (TCBMA), is designed, modeled, and optimized using the SCAPS-1D simulator, which focuses primarily on investigating the influence of various parameters on the solar cell. The simulated device achieves a high power conversion efficiency of 38.83% with Jsc = 32.40 mA/ \(\hbox {cm}^2\) , Voc = 1.3498 V, and FF = 88.78%. The optimized performance parameters are achieved by careful selection and stacking of functional layers. Fluorine-doped tin oxide (FTO) provides transparency and conductivity, \(\hbox {WS}_2\) functions as a robust electron transport layer, \(\hbox {MgHfS}_3\) offers strong optical absorption and thermal stability, Cs2PtI6 enhances structural and electronic quality, and Spiro-OMeTAD ensures efficient hole transport. Collectively, these features enable superior charge extraction, reduced recombination, and enhanced durability. The proposed device structure ensures sustainable, high-efficiency photovoltaics and offers a roadmap for advanced experimental validation and simulation of high-efficiency and stable TCBMA solar cells for next-generation photovoltaic technology.
