Mixed-cation mixed-halide perovskites have gained a lot of attention due to their superior device properties, optoelectronic properties, and improved structural stabilities over methyl ammonium lead trihalide-based devices. However, understanding the interfacial charge and ion transport kinetics remains elusive. In this article, we have synthesized (MA)_x(FA)_x−1Pb(Br)_2+x(I)_1–x stoichiometric compositions by varying x between 0.2 and 1.0. We have chosen two compositions with x = 0.6 and 0.8 due to their similar morphologies and optical absorption properties. We have demonstrated that increasing MA⁺ for x = 0.6–0.8 can reduce the ion migration by a factor of two while the activation energy for ion migration is increased from 0.36 eV to 0.47 eV. The ideality factor can be reduced upon increasing methylammonium bromide concentrations. We have measured ionic conductivity as a function of frequency to demonstrate that the interplay between A-site cation and X-site halide ion leads to opposite behavior in the low-frequency regime upon increasing bias voltage. This could be due to two competing processes; interfacial polarization and cation-halide hydrogen bonding in two samples. MA⁺ and FA⁺ migration lead to Jonscher’s power law at the mid-frequency regime. High-frequency AC conductivity follows the nearly constant (dielectric) loss regime with exponent (slope) exceeding one due to the presence of multiple ions in the systems. This kind of super-linear power law behavior of AC ionic conductivity at operating temperature is reported for the first time in these perovskite materials.

中文翻译：

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A-位阳离子和X-位卤化物相互作用在混合阳离子混合卤化物钙钛矿中确定工作温度下AC离子电导率的异常高理想因子和超线性幂律的作用

混合阳离子混合卤化物钙钛矿因其优越的器件性能，光电性能以及与基于甲基铵三卤化铅的器件相比更高的结构稳定性而倍受关注。但是，了解界面电荷和离子传输动力学仍然很困难。在本文中，我们通过在0.2和1.0之间改变x来合成（MA）_x（FA）_{x -1} Pb（Br）_{2+ x}（I）_{1– x}化学计量组成。由于它们具有相似的形态和光吸收特性，我们选择了x = 0.6和0.8的两种成分。我们已经证明，增加MA ⁺为X= 0.6–0.8可以将离子迁移减少两倍，而离子迁移的激活能从0.36 eV增加到0.47 eV。增加甲基溴化铵浓度可以降低理想因子。我们已经测量了离子电导率随频率的变化，以证明A位阳离子和X位卤化物离子之间的相互作用在增加偏置电压的情况下在低频范围内导致相反的行为。这可能是由于两个相互竞争的过程所致；两个样品中的界面极化和阳离子卤化物氢键。MA ⁺和FA ⁺迁移导致中频政权的琼斯幂律。高频交流电导率遵循几乎恒定的（介电）损耗方式，由于系统中存在多个离子，因此指数（斜率）超过1。这些钙钛矿材料中首次报道了这种交流离子电导率在工作温度下的超线性幂律行为。