Exploring the potential of lead-free ASnI2Br-based tandem 4 T and 2 T configurations: a comprehensive TCAD analysis

To meet the growing demand for eco-friendly solar technologies, lead-free perovskite (PVK) materials are emerging as promising alternatives to their lead-based counterparts. Among these, ASnI₂Br stands out due to its suitable wide bandgap, making it a strong candidate for integration into both 4T and 2T tandem configurations. In pursuit of a fully eco-friendly solar cell design, we present the development of lead-free ASnI₂Br/Si tandem solar cells, offering a sustainable approach with high potential for efficiency improvements. First, the advancement of 4 T tandem cell efficiency is discussed. The main structure consists of FTO/PEDOT:PSS/ASnI₂Br-PVK/C₆₀/BCP/Ag inverted structure as the top cell and an n-type Si as the rear cell. Based on the simulation findings, the suggested top cell structure performs much better when TiO₂ is substituted as the electron transport layer instead of C₆₀, while CuSCN is found to be a good replacement for PEDOT:PSS as a hole transport layer. With these changes, the top cell's efficiency becomes 15.29%. In addition, optimizations for the bottom cell are carried out. Efficiencies for bare and filtered bottom cells reaching 23.97 and 12.53% are achieved, respectively, at 30 µm absorber thickness and 1 ms lifetime. With only two terminals, the 2 T cell has fewer manufacturing costs for the photovoltaic module than the 4 T cell. Thus, we introduce a design for a 2 T cell by converting the enhanced 4 T cell, while inverting the top cell to be compatible with the rear cell n-p structure. To ensure current matching, the correct thickness must be established for both sub-cells, where the thickness of the perovskite absorption layer rises from 200 to 545 nm. This led to reaching the matching point at a current equal to 16.35 mA/cm², and our simulation for the monolithic stacked 2T TSC produced a PCE of 24.28%.