Rahman Muhammad Akif, Giri Ashutosh
Department of Mechanical, Industrial, and Systems Engineering, University of Rhode Island, Kingston, Rhode Island 02881, USA.
J Chem Phys. 2021 Sep 28;155(12):124703. doi: 10.1063/5.0065207.
The complete understanding of the mechanical and thermal responses to strain in hybrid organic-inorganic perovskites holds great potential for their proper functionalities in a range of applications, such as in photovoltaics, thermoelectrics, and flexible electronics. In this work, we conduct systematic atomistic simulations on methyl ammonium lead iodide, which is the prototypical hybrid inorganic-organic perovskite, to investigate the changes in their mechanical and thermal transport responses under uniaxial strain. We find that the mechanical response and the deformation mechanisms are highly dependent on the direction of the applied uniaxial strain with a characteristic ductile- or brittle-like failure accompanying uniaxial tension. Moreover, while most materials shrink in the two lateral directions when stretched, we find that the ductile behavior in hybrid perovskites can lead to a very unique mechanical response where negligible strain occurs along one lateral direction while the length contraction occurs in the other direction due to uniaxial tension. This anisotropy in the mechanical response is also shown to manifest in an anisotropic thermal response of the hybrid perovskite where the anisotropy in thermal conductivity increases by up to 30% compared to the unstrained case before plastic deformation occurs at higher strain levels. Along with the anisotropic responses of these physical properties, we find that uniaxial tension leads to ultralow thermal conductivities that are well below the value predicted with a minimum thermal conductivity model, which highlights the potential of strain engineering to tune the physical properties of hybrid organic-inorganic perovskites.
全面理解有机-无机杂化钙钛矿对应变的机械和热响应，对于其在一系列应用（如光伏、热电和柔性电子）中的正常功能具有巨大潜力。在这项工作中，我们对典型的有机-无机杂化钙钛矿甲基碘化铅进行了系统的原子模拟，以研究其在单轴应变下机械和热输运响应的变化。我们发现，机械响应和变形机制高度依赖于所施加单轴应变的方向，单轴拉伸时伴有典型的韧性或脆性破坏。此外，虽然大多数材料在拉伸时会在两个横向方向收缩，但我们发现杂化钙钛矿中的韧性行为会导致一种非常独特的机械响应，即由于单轴拉伸，在一个横向方向上应变可忽略不计，而在另一个方向上发生长度收缩。这种机械响应的各向异性在杂化钙钛矿的各向异性热响应中也有体现，在较高应变水平发生塑性变形之前，与未受应变的情况相比，热导率的各向异性增加高达30%。伴随着这些物理性质的各向异性响应，我们发现单轴拉伸会导致超低的热导率，远低于用最小热导率模型预测的值，这突出了应变工程调控有机-无机杂化钙钛矿物理性质的潜力。
