Tandem solar cells employing lead-free perovskite materials offer a compelling pathway to simultaneously achieve high power conversion efficiency (PCE) and improved environmental sustainability. In this work, we present a comprehensive numerical simulation study of monolithic and mechanically stacked tandem solar cells based on the chalcogenide perovskite BaZrS3 as the top subcell and Cu(In,Ga)Se2 (CIGS) as the bottom subcell. For the four-terminal (4-T) configuration, a systematic optimization workflow was implemented, encompassing the thickness of absorber and carrier-transport layers, doping concentrations, and the introduction of a LiF anti-reflection coating. This approach led to a marked reduction in parasitic absorption and reflection losses, ultimately yielding a champion PCE of 34.7%. In the two-terminal (2-T) series-connected tandem, current matching was achieved by tuning the Ga content in the CIGS bottom absorber, which adjusts its bandgap and spectral response. Further co-optimization of doping profiles in the transport layers and the CIGS absorber resulted in a maximum PCE of 32.65%. Our analysis also highlights that the defect density within the BaZrS3 layer is a critical performance governor; increasing trap densities severely degrade open-circuit voltage and fill factor, underscoring the importance of high-quality perovskite film synthesis. The results demonstrate the considerable potential of the eco-friendly BaZrS3/CIGS tandem architecture for next-generation photovoltaics.
Zhang et al. (Thu,) studied this question.