Elastic Properties of Photovoltaic Single Crystal Cs₂AgBiBr₆

Background: Halide double perovskite Cs₂AgBiBr₆ shows promising potential applications in next-generation photovoltaic devices. The strain engineering strategy has been proven as a reliable method to improve its performance. The fundamental physical tensor of elastic constants C_ij has not been accurately measured yet, due to the limited size of samples. Objective: The aim of this work is to measure its full elastic tensor C_ij using various techniques. Methods: We utilized nanoindentation and contact resonance atomic force microscopy (CR-AFM) techniques to measure the elastic modulus on an as-grown facet, which is along the [111] direction. Then, the inelastic X-ray scattering (IXS) approach and density functional theory were introduced to obtain the accurate full elastic constant C_ij of single crystal Cs₂AgBiBr₆. Results: The full elastic constants were measured as C₁₁ = 44.52 GPa, C₁₂ = 17.63 GPa and C₄₄ = 8.56 GPa. The results for the modulus along the [111] direction reveal that nanoindentation and CR-AFM are sufficiently reliable for quantitative measurements of small single crystals Cs₂AgBiBr₆. Conclusions: The results provide guidelines for strain engineering in the photovoltaic applications using Cs₂AgBiBr₆ and for elastic property measurements in nanomaterials.