Unveiling Pressure-Driven Transitions in Cs₂AgBiBr₆: Insights from DFT into a Lead-Free Solar Perovskite
Abstract
Using the Vienna Ab initio Simulation Package, we investigate the lead-free double perovskite Cs₂AgBiBr₆. We used first-principles density functional theory under pressures up to 30 GPa. Optimization of the structure proves an obvious cubic symmetry in the ambient environment. However, compression appears to promote transitions to lower-symmetry phases, and we observe that the bulk and Young's moduli increase, followed by a decrease in Poisson's ratio. This implies more stiffness but reduced ductility. It is concluded that, as temperature increases, the Debye temperature rises and the thermal expansion decreases. Thus, higher temperature stability is suggested. The electronic bandgap becomes even thinner. It spans 1.95 eV to 1.12 eV, making it more or less direct, which may enhance its optoelectronic usability. Above 15 GPa, we observe a weak magnetic moment, apparently due to Bi–Ag hybridization, and a higher density of states at the Fermi level. Cs₂AgBiBr₆ combines these characteristics, making it a potential material for pressure-tuned photovoltaics and potentially for magneto-optoelectronic applications.
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