Liu Yongtao, Trimby Patrick, Collins Liam, Ahmadi Mahshid, Winkelmann Aimo, Proksch Roger, Ovchinnikova Olga S
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States.
Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States.
ACS Nano. 2021 Apr 27;15(4):7139-7148. doi: 10.1021/acsnano.1c00310. Epub 2021 Mar 26.
Metal halide perovskite (MHP) solar cells have attracted worldwide research interest. Although it has been well established that grain, grain boundary, and grain facet affect MHPs optoelectronic properties, less is known about subgrain structures. Recently, MHP twin stripes, a subgrain feature, have stimulated extensive discussion due to the potential for both beneficial and detrimental effects of ferroelectricity on optoelectronic properties. Connecting the ferroic behavior of twin stripes in MHPs with crystal orientation will be a vital step to understand the ferroic nature and the effects of twin stripes. In this work, we studied the crystallographic orientation and ferroic properties of CHNHPbI twin stripes, using electron backscatter diffraction (EBSD) and advanced piezoresponse force microscopy (PFM), respectively. Using EBSD, we discovered that the orientation relationship across the twin walls in CHNHPbI is a 90° rotation about ⟨1̅1̅0⟩, with the ⟨030⟩ and ⟨111⟩ directions parallel to the direction normal to the surface. By careful inspection of CHNHPbI PFM results including in-plane and out-of-plane PFM measurements, we demonstrate some nonferroelectric contributions to the PFM responses of this CHNHPbI sample, suggesting that the PFM signal in this CHNHPbI sample is affected by nonferroelectric and nonpiezoelectric forces. If there is piezoelectric response, it is below the detection sensitivity of our interferometric displacement sensor PFM (<0.615 pm/V). Overall, this work offers an integrated picture describing the crystallographic orientations and the origin of PFM signal of MHPs twin stripes, which is critical to understanding the ferroicity in MHPs.
金属卤化物钙钛矿（MHP）太阳能电池已引起全球研究关注。尽管人们已经充分认识到晶粒、晶界和晶面会影响MHP的光电性能，但对于亚晶粒结构的了解却较少。最近，MHP孪晶条纹作为一种亚晶粒特征，因其铁电性对光电性能可能产生的有益和有害影响而引发了广泛讨论。将MHP中孪晶条纹的铁性行为与晶体取向联系起来，将是理解孪晶条纹铁性本质及其影响的关键一步。在这项工作中，我们分别使用电子背散射衍射（EBSD）和先进的压电响应力显微镜（PFM）研究了CHNHPbI孪晶条纹的晶体取向和铁性特性。通过EBSD，我们发现CHNHPbI中孪晶界两侧的取向关系是绕〈1̅1̅0〉旋转90°，〈030〉和〈111〉方向平行于表面法线方向。通过仔细检查CHNHPbI的PFM结果，包括面内和面外PFM测量，我们证明了该CHNHPbI样品的PFM响应存在一些非铁电贡献，这表明该CHNHPbI样品中的PFM信号受到非铁电和非压电作用力的影响。如果存在压电响应，其低于我们的干涉式位移传感器PFM的检测灵敏度（<0.615 pm/V）。总体而言，这项工作提供了一幅描述MHP孪晶条纹晶体取向和PFM信号起源的综合图景，这对于理解MHP中的铁性至关重要。
