Stabilizing lead-free all-inorganic tin halide Perovskites by ion exchange

Due to its thermal stability, lead-free composition and nearly ideal optical and electronic properties, orthorhombic CsSnI3 perovskite is considered promising as a light absorber for lead-free all-inorganic perovskite solar cells (PSCs) [1,2]. However, the susceptibility of this 3-dimensional perovskite towards oxidation in air has limited the development of solar cells based on this material [1]. 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 [3, 4]. We show the evolution of the electronic structure, as well as 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 for x>=1/3. We predict that substitution of Cs with Rb results in a highly homogeneous solid solution and therefore an improved film quality and applicability in solar cell devices. These predictions point the way to the realization of air-stable all-inorganic tin halide perovskites for both single and tandem junction solar cell applications.