In this paper, a new Se/CZTSSe tandem solar cell architecture is proposed as a viable approach to reach ultrahigh efficiency values at low fabrication cost. The proposed tandem design consists of a Se-based top cell with Ti intermediate ultra-thin metallic layers (MLs) and a CZTS bottom cell with graded band-gap aspect. The role of the introduced design amendments in achieving the dual-benefit of enhanced optical behavior and reduced recombination losses is investigated by means of an accurate numerical modeling. Moreover, a comprehensive study which involves the impact of design parameters such as the MLs position and the CZTSSe band-gap profile on the device performance is carried out. Moreover, Particle Swarm Optimization (PSO)-based metaheuristic technique is used to boost up the Se/CZTSSe tandem cell efficiency by identifying both the suitable position of the introduced ultrathin MLs and the appropriate CZTSSe band-gap profile. It is found that the adopted optimization approach pinpoints a new path toward achieving over 30% efficiency, not only it provides the possibility to reduce interface recombination effects by optimizing the band offset at the buffer/absorber interfaces but also enables selecting the most favorable design configuration associated with enhanced optical behavior. This makes the optimized Se/CZTSSe tandem solar cell potential alternative for providing high-efficiency and stable tandem solar cell.

In this paper, a new Se/CZTSSe tandem solar cell architecture is proposed as a viable approach to reach ultrahigh efficiency values at low fabrication cost. The proposed tandem design consists of a Se-based top cell with Ti intermediate ultra-thin metallic layers (MLs) and a CZTS bottom cell with graded band-gap aspect. The role of the introduced design amendments in achieving the dual-benefit of enhanced optical behavior and reduced recombination losses is investigated by means of an accurate numerical modeling. Moreover, a comprehensive study which involves the impact of design parameters such as the MLs position and the CZTSSe band-gap profile on the device performance is carried out. Moreover, Particle Swarm Optimization (PSO)-based metaheuristic technique is used to boost up the Se/CZTSSe tandem cell efficiency by identifying both the suitable position of the introduced ultrathin MLs and the appropriate CZTSSe band-gap profile. It is found that the adopted optimization approach pinpoints a new path toward achieving over 30% efficiency, not only it provides the possibility to reduce interface recombination effects by optimizing the band offset at the buffer/absorber interfaces but also enables selecting the most favorable design configuration associated with enhanced optical behavior. This makes the optimized Se/CZTSSe tandem solar cell potential alternative for providing high-efficiency and stable tandem solar cell.