Understanding the relationship between the crystal structure elastic–plastic properties of discrete-molecule organic–inorganic halide perovskites†

Abstract

Discrete-molecule hybrid perovskites with different organic and inorganic molecules can provide a wide array of tunable optoelectronic and piezoelectronic properties. In this study, we report the elastic modulus and hardness, obtained from instrumented indentation measurements, of three new and three known discrete-molecule single crystal halide metalates, with an aim towards understanding the relationship between their microstructure and mechanical properties. We find a correlation in the mechanical properties and the density of the crystal structure, as well as with the number of hydrogen bonding sites available on the organic cation. These two observations suggest that denser crystal structures with more hydrogen bonding sites lead to stronger intermolecular interactions, thereby increasing the elastic modulus. Contrary to previous findings in the literature, we also find that the metal–halide bond strength does not significantly influence the elastic modulus in this set of data. We rationalize this observation by the differences in supramolecular network dimensionality between the literature reports and the crystals presented in this study, thus concluding that the metal–halide bond strength plays an insignificant role in determining the elasticity of discrete-molecule single crystal hybrid perovskites.