Study of the Long-Term Ambient Stability of Perovskite Alloys MAPb(I1−xBrx)3: Identification of the Optimal Halide Ratio

Hybrid halogenated perovskites MAPb(I1−xBrx)3 are attracting increasing interest due to their remarkable optoelectronic performance, particularly in solar cells. However, their instability under ambient conditions remains a major obstacle to their commercialization. This work presents a systematic study of the structural, morphological, and optical properties of perovskite thin films MAPb(I1−xBrx)3 (x = 0 to 0.15) as well as their stability under ambient conditions. The main objective is to identify the optimal I/Br ratio that maximizes structural and optical stability without compromising electronic properties. The films were prepared by centrifugation with toluene as an antisolvent, followed by controlled thermal annealing. Degradation was monitored over several weeks using characterization techniques such as X-ray diffraction (XRD), UV-Visible spectroscopy, and photoluminescence. X-ray diffraction (XRD) and UV-Visible spectroscopy analyses confirm the efficient incorporation of bromine, resulting in lattice contraction and a controlled band gap widening from 1.60 eV to 1.68 eV. The degradation evolution over 28 days shows that while the MAPbI3 pure form amorphizes in less than a week, the addition of bromine significantly delays this process. The sample with 10% Br is identified as the optimum, exhibiting exceptional electronic resilience with a fourfold increase in photoluminescence intensity during aging.