Organic–inorganic halide perovskites (OIHPs) have the typical composition of APbX₃, in which A is a cation such as methlyamine (MA) and formamidine (FA) and X is a halide anion such as Cl, Br, or I. The mixture at the A or X site in OIHPs provides greatly improved versatility in their compositions and therefore allows the enhancement of their performance in LEDs and solar cells. In real application circumstances and deformable devices, the mechanical properties of OIHPs are of great importance. In this work, the mechanical properties of three series of mixed OIHP single crystals, MAPbI_xBr_3−x, MAPbBr_xCl_3−x, and FA_yMA_1−yPbBr₃, are studied by nanoindentation. The results are summarized according to the composition of these mixtures. With the increase in the FA content at the A site, the average Young’s modulus (E) of FA_yMA_1−yPbBr₃ decreases greatly from 19.2 GPa to 11.5 GPa, which indicates that the influence of organic cations on the mechanical properties of OIHPs is as important as that of Pb-X bonds. The mixture at the A or X site could also increase the hardness (H) and the wear resistance (H/E ratio). The average values of hardness and wear resistance of MAPbI_0.1Br_2.9 are almost double (0.63 GPa, 0.033) the values for undoped MAPbBr₃ (0.32 GPa, 0.017). The dynamic mechanical responses of the OIHP single crystals show reduced creep stress exponents and thus increased strain rate sensitivities in the mixture at the X site, thereby improving the ductility. The nanoindentation sites are characterized using a scanning electron microscope and slip bands are observed, suggesting the plastic deformation mechanism governed by the activation of dislocations.

中文翻译：

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A或X位点混合物对APbX3钙钛矿单晶力学性能的影响

有机-无机卤化物钙钛矿（OIHPs）具有典型的A Pb X _3组成，其中A是阳离子，例如甲胺（MA）和甲am（FA），X是卤化物阴离子，例如Cl，Br或I。OIHP中A或X位置的混合物极大地提高了其组成的多功能性，因此可以增强其在LED和太阳能电池中的性能。在实际应用环境和可变形设备中，OIHP的机械性能非常重要。在这项工作中，三个混合的OIHP单晶MAPbI _x Br _{3- x}，MAPbBr的力学性能通过纳米压痕研究了_x Cl _{3- x}和FA _y MA _{1- y} PbBr ₃。根据这些混合物的组成总结了结果。随着A部位FA含量的增加，FA _y MA _{1 － y} PbBr ₃的平均杨氏模量（ E）从19.2 GPa大大降低至11.5 GPa，这表明有机阳离子对A的力学性能的影响。 OIHP与Pb- X键一样重要。在A或X位置的混合物也会增加硬度（H）和耐磨性（H / E比）。MAPbI _0.1 Br _2.9的硬度和耐磨性平均值几乎是未掺杂MAPbBr ₃（0.32 GPa，0.017）的两倍（0.63 GPa，0.033 ）。OIHP单晶的动态力学响应显示出降低的蠕变应力指数，从而提高了X位置处混合物的应变速率敏感性，从而提高了延展性。使用扫描电子显微镜对纳米压痕部位进行表征，并观察到滑移带，这表明由位错激活控制的塑性变形机制。