Lead halide perovskites are mixed electronic–ionic semiconductors that have recently revolutionized the photovoltaics field. The physical characterization of the ionic conductivity has been rather elusive because of the high intermixing of ionic and electronic current. In this work, the synthesis of low defect density monocrystalline MAPbBr₃ (MA = methylammonium) solar cells free of a hole transport layer (HTL) suppresses the effect of electronic current. Impedance spectroscopy reveals the characteristic signature of ionic diffusion (the Warburg element and transmission line equivalent circuit) and ion accumulation at the interface of MAPbBr₃ with the external contacts. Diffusion coefficients are calculated based on a good correlation between thickness of MAPbBr₃ and characteristic diffusion transition frequency. In addition, reactive external interfaces are studied by comparison of polycrystalline MAPbBr₃ devices prepared either with or without a HTL. The low-frequency response in impedance spectroscopy measurements is correlated with the chemical reactivity of moving ions with the external interfaces and diffusion into the HTL.

中文翻译：

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卤化钙钛矿型单晶中离子扩散的定量

卤化钙钛矿是混合的电子离子半导体，最近已彻底改变了光伏领域。由于离子电流和电子电流的高度混合，所以离子电导率的物理表征难以捉摸。在这项工作中，无空穴传输层（HTL）的低缺陷密度单晶MAPbBr ₃（MA =甲基铵）太阳能电池的合成抑制了电流的影响。阻抗谱揭示了离子扩散（Warburg元件和传输线等效电路）和MAPbBr ₃与外部触点的界面处的离子积累的特征标记。基于MAPbBr _3的厚度之间的良好相关性来计算扩散系数和特征扩散跃迁频率。此外，通过比较在有无HTL的情况下制备的多晶MAPbBr ₃器件，研究了反应性外部界面。阻抗谱测量中的低频响应与移动离子与外部界面以及扩散到HTL中的化学反应性相关。