This paper uses 3D finite element method (FEM) to investigate the optoelectrical properties of a four terminal (4T) lead-free all perovskite tandem solar cell (AP-TSC). The plasmonic nanoparticles (NPs)-free structure serves as a reference structure. In this structure, the top/bottom sub-cells’ power conversion efficiency (PCE) as well as the total PCE are 19.59% (12.64%) and 32.23%, respectively. Next, an approach to enhance PCE is proposed: NPs-based structure. After the results for the reference structure are confirmed, the impacts of adding plasmonic NPs assisted light scattering mechanism to the narrow bandgap (NBG) absorber layer on the suggested structure’s electrical and optical characteristics are examined. We investigate the effects of the NPs’ size (R), periodicity (P), material, and location on the proposed structure’s optoelectrical characteristics. The highest total PCE was obtained by adding Ag NPs to the middle part of NBG absorber layer under the optimal conditions of (R, P) (120, 300) nm. The final NPs-based structure with optimal conditions is proposed as 4T AP-TSC that is environmentally friendly, with bottom sub-cell and total PCEs of 13.94% and 33.53%, 1.3% more PCE than the reference structure.
