Probing the Soft and Nanoductile Mechanical Nature of Single and Polycrystalline Organic–Inorganic Hybrid Perovskites for Flexible Functional Devices

详细信息    查看全文

• 作者：Jingui Yu ; Mingchao Wang ; Shangchao Lin
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：December 27, 2016
• 年：2016
• 卷：10
• 期：12
• 页码：11044-11057
• 全文大小：965K
• ISSN：1936-086X

文摘

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 MAPbI₃ is 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 MAPbI₃ exhibits 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 MAPbI₃ with 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.