title: Probing the Soft and Nanoductile Mechanical Nature of Single and Polycrystalline Organic-Inorganic Hybrid Perovskites for Flexible Functional Devices.
abstract: Although organic-inorganic hybrid perovskites have been extensively investigated for promising applications in energy-related devices, their mechanical properties, which restrict their practical deployment as flexible and wearable devices, have been largely unexplored at the atomistic level. Toward this level of understanding, we predict the elastic constant matrix and various elastic properties of CH3NH3PbI3(MAPbI3) using atomistic simulations. We find that single-crystalline MAPbI3is much stiffer and exhibits higher ultimate tensile strength than polycrystalline samples, but the latter exhibit unexpected, greatly enhanced nanoductility and fracture toughness, resulting from the extensive amorphization during the yielding process. More interestingly, polycrystalline MAPbI3exhibits inverse Hall-Petch grain-boundary strengthening effect, in which the yield stress is reduced when decreasing the grain size, due to amorphous grain boundaries. By monitoring the centro-symmetry parameter and local stress evolution, we confirm the soft and nanoductile nature of defective MAPbI3with a crack. By conducting atomic stress decomposition, we attribute such fracture toughness primarily to the strong electrostatic interactions between the ionic components. The observed limited brittle fracture behavior is attributed to the transformation of partial edge dislocations to disordered atoms (nanovoid formation). A significant plastic deformation region is observed when nanovoids enlarge and coalesce with adjacent ones, which ultimately leads to crack propagations via ionic-chain breaking. After comparing with traditional inorganic energy-related materials, we find that hybrid perovskites are more compressible and can absorb more strain energy before fracture, which makes them well suited for wearable functional devices with high mechanical flexibility and robustness.
authors.affiliation: Department of Mechanical Engineering, Materials Science and Engineering Program, FAMU-FSU College of Engineering, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: Jingui
authors.initials: J
authors.lastname: Yu
authors.affiliation: Department of Mechanical Engineering, Materials Science and Engineering Program, FAMU-FSU College of Engineering, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: Mingchao
authors.initials: M
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, Materials Science and Engineering Program, FAMU-FSU College of Engineering, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: Shangchao
authors.identifier: 0000-0002-6810-1380
authors.initials: S
authors.lastname: Lin
keywords: crack propagation; fracture mechanics; hybrid perovskite; microstructural evolution; molecular dynamics; polycrystalline thin films