Degradation Studies of Cs₃Sb₂I₉: A Lead-Free Perovskite

Lead-free halide perovskites have attracted interest in the photovoltaic industry out of concern for the toxic nature of the lead. Antimony-based perovskite, cesium antimony iodide (Cs3Sb2I9), is one such material proposed to substitute the lead-based perovskites, as it has a high absorption coefficient, nearly direct bandgap, and low effective mass. A clear understanding of the stability of this material will bring out its efficient use in photovoltaics. Here we have studied the degradation of both the polymorphs of Cs3Sb2I9 (dimer and layer forms) in water, light, and elevated temperature—the well-known factors causing degradation in perovskites using X-ray diffraction and thermogravimetric analysis. The layered polymorph is found to be more stable compared to the dimer polymorph. The dimer form completely degrades in ∼49 days and the layer form in ∼88 days, although both polymorphs of Cs3Sb2I9 are relatively more stable than the established organic–inorganic halide perovskites. We found that the diffusion of iodine from the system is the prime reason for the degradation in Cs3Sb2I9. Also, the reactivity of antimony iodide (SbI3) in oxygen adds up to accelerate the degradation process. Light, water, and heat equally cause the degradation of Cs3Sb2I9, and hence, use of this material for application in the ambient atmosphere would need proper encapsulation or necessary measures.