High-efficiency design of non-toxic Cs₂TiF₆ double perovskite absorbers: optimized single absorber, bilayer absorber, and top cell for two-terminal tandems

In the present work, the feasibility of a lead-free double perovskite Cs₂TiF₆ as a replacement for lead-based perovskite materials in solar cell applications is investigated. This double perovskite material exhibits noteworthy benefits, including a high absorption coefficient, enhanced stability, reduced reflectivity, and an optimal bandgap, thus stands as an alluring option for efficient photovoltaic applications. This investigation employed SCAPS-1D software for the modeling and simulation of the FTO/ZnOS/Cs₂TiF₆/Cu₂O structure. The primary objective was to assess the photovoltaic properties of the material in relationship to a wide range of physical parameters, especially absorber thickness, interface defect density, metal work function, acceptor concentration, shunt resistance and series resistance, operating temperature, and quantum efficiency. Upon parameter optimization, the proposed single-halide Cs₂TiF₆-based structure obtains a short-circuit current density of 15.06 mA/cm², an open-circuit voltage of 1.52 V, maximum power conversion efficiency of 20.42%, and a fill factor of 88.81%. The potential of Cs₂TiF₆ in bilayer heterojunction structure was also investigated, achieving an impressive power conversion efficiency of 21.22% and 24.24% for Cs₂TiF₆/CsPbI₃ and Cs₂TiF₆/CsSnI₂Br based perovskite solar cells. In addition, the two terminal tandem devices based on c-Si as bottom cell and Cs₂TiF₆ as the top cell exhibited impressive PCE. Thus, the research implies that Cs₂TiF₆ double perovskites could be an essential absorber layer for solar cell technology.