Because
of its thermal stability, lead-free composition, and nearly
ideal optical and electronic properties, the orthorhombic CsSnI3 perovskite is considered promising as a light absorber for
lead-free all-inorganic perovskite solar cells. However, the susceptibility
of this three-dimensional perovskite toward oxidation in air has limited
the development of solar cells based on this material. Here, we report
the findings of a computational study which identifies promising RbyCs1–ySn(BrxI1–x)3 perovskites for solar cell applications, prepared by substituting
cations (Rb for Cs) and anions (Br for I) in CsSnI3. We
show the evolution of the material electronic structure as well as
its thermal and structural stabilities upon gradual substitution.
Importantly, we demonstrate how the unwanted yellow phase can be suppressed
by substituting Br for I in CsSn(BrxI1–x)3 with x ≥ 1/3. We predict that substitution of Rb for Cs results
in a highly homogeneous solid solution and therefore an improved film
quality and applicability in solar cell devices.