  The significant surge in energy use and escalating environmental concerns
have sparked worldwide interest towards the study and implementation of solar
cell technology. Perovskite solar cells (PSCs) have garnered remarkable
attention as an emerging third-generation solar cell technology. This paper
presents an in-depth analysis of lead-free mixed halide double perovskites in
the context of their potential uses in solar cell technology. Through the
previous studies of various mixed halide double perovskite materials as
potential absorber layer materials, it has been observed that
Cs$_2$TiI$_{6-x}$Br$_x$ possesses promising characteristics. In this study,
simulations were conducted using SCAPS-1D software to explore all possible
combinations for x= 0 to 6. The materials for the Hole Transport Layer (HTL)
and Electron Transport Layer (ETL) and absorber layer, along with their optimal
thicknesses, are selected to yield the most promising results in terms of
open-circuit voltage (V$_{oc}$), short-circuit current density (J$_{sc}$), fill
factor (FF), and power conversion efficiency. A novel tolerance factor is
employed to assess structural stability of perovskites.
FTO/Cu$_2$O/Cs$_2$TiI$_5$Br$_1$/WS$_2$ emerges as the best combination in terms
of the efficiency with 19.03% but FTO/Cu$_2$O/Cs$_2$TiI$_2$Br$_4$/WS$_2$ shows
good stability with 13.31% efficiency.
