A numerical approach for optimization of bismuth-based photo absorbers for solar cell applications

The present study focuses on the potential of utilizing bismuth (Bi)-based materials as alternate lead (Pb)-free and environmentally stable photo absorbers in single and multi-junction solar cells. In this work, using SCAPS-1D simulation software, the performance of Bi-based materials: AgBiS₂ (bandgap (E_g) = 1.32 eV), Cs₂AgBiBr₆ (E_g = 2.03 eV), MA₃Bi₂I₉ (E_g = 2.26 eV), and bismuth triiodide (BiI₃) (E_g = 1.8 eV) are analyzed in planar single-junction solar cell configuration by employing different electron transport layers (ETLs) namely TiO₂, SnO₂, ZnO, and PCBM and different hole transport layers (HTLs) like Spiro-OMeTAD, PEDOT: PSS, PTAA, Cu₂O, CuSCN, and NiO. The simulations achieved promising power conversion efficiencies (PCEs) of 11.33% and 14.87% for the AgBiS₂ and Cs₂AgBiBr₆ solar cells respectively. Thereafter, we optimized the thickness of the absorber layer and examined the mechanisms of charge carrier transport and recombination processes by analyzing the effects of varying temperatures and light intensity on the device’s performance. Finally, with the help of script setup in SCAPS-1D, a two-terminal tandem solar cell (2T-TSC) was designed by connecting the Cs₂AgBiBr₆ and AgBiS₂ solar cells in series as the top and bottom subcell respectively which showed a promising PCE of over 27%.