Lead-free perovskite-type materials, renowned for their easy processing and tunable bandgaps, have emerged as a cost-effective alternative for fabricating high-efficiency tandem solar cells. Utilizing density functional theory (DFT) combined with the full-potential linearized augmented plane wave (FP-LAPW) method and the modified Becke-Johnson exchange potential (TB-mBJ), this study investigates the potential of CaBS (B = Zr, Hf, and Sn) compounds as promising absorbers for next-generation tandem applications. Our results demonstrate that CaBS compounds exhibit semiconducting properties with direct bandgaps. This study investigates the unique properties of CaBS perovskites, revealing their potential to enhance the efficiency of next-generation photovoltaic devices. Our findings demonstrate that CaZrS exhibits a remarkable Seebeck coefficient of up to 3200 V/K, indicating superior p-type conduction and enhanced thermoelectric efficiency. Furthermore, the direct bandgaps and ambipolar conductive behavior of these materials position them as strong candidates for photovoltaic applications. Notably, a four-terminal tandem solar cell configuration comprising CaZrS and CaSnS achieves a peak conversion efficiency of 55.5% at an absorber thickness of 500 nm, surpassing the traditional Shockley–Queisser limit. These results underscore the promising capabilities of CaBS perovskites in advancing renewable energy technologies, paving the way for innovative designs in solar energy solutions. This investigation lends empirical credence to the optimization of tandem cell designs, thus catalyzing advancements in next-generation photovoltaic technologies.