Mechanical properties of organic–inorganic halide perovskites, CH3NH3PbX3 (X = I, Br and Cl), by nanoindentation

Abstract

We report an experimental study of the mechanical properties of the organic–inorganic halide perovskites, CH₃NH₃PbX₃ (X = I, Br and Cl). Nanoidentation on single crystals was used to obtain Young's moduli (E) and hardnesses (H) of this class of hybrid materials, which have attracted considerable attention for photovoltaic applications. The measured Young's moduli of this family lie in the range 10–20 GPa and a trend of E_Cl > E_Br > E_I is observed. The physical properties are consistent with the underlying crystal structure. In particular, the results are in reasonable agreement with recent calculations using density functional theory and align with expectations based upon bond energy, packing, and hydrogen-bonding considerations. The anisotropy in these systems is quite small, with E₁₀₀ > E₁₁₀ for the cubic bromide and chloride cases and E₁₁₂ ≈ E₁₀₀ for the tetragonal iodide perovskites. Interestingly, CH₃NH₃PbI₃ is harder than the Br- and Cl-based perovskites.