We show for the first time that the frontier orbital energetics (conduction band minimum (CBM) and valence band maximum (VBM)) of device-relevant, methylammonium bromide (MABr)-doped, formamidinium lead trihalide perovskite (FA-PVSK) thin films can be characterized using UV-vis spectroelectrochemistry, which provides an additional and straightforward experimental technique for determining energy band values relative to more traditional methods based on photoelectron spectroscopy. FA-PVSK films are processed via a two-step deposition process, known to provide high efficiency solar cells, on semitransparent indium tin oxide (ITO) and titanium dioxide (TiO2) electrodes. Spectroelectrochemical characterization is carried out in a nonsolvent electrolyte, and the onset potential for bleaching of the FA-PVSK absorbance is used to estimate the CBM, which provides values of ca. -4.0 eV versus vacuum on both ITO and TiO2 electrodes. Since electron injection occurs from the electrode to the perovskite, the CBM is uniquely probed at the buried metal oxide/FA-PVSK interface, which is otherwise difficult to characterize for thick films. UPS characterization of the same FA-PVSK thin films provide complementary near-surface measurements of the VBM and electrode-dependent energetics. In addition to energetics, controlled electrochemical charge injection experiments in the nonsolvent electrolyte reveal decomposition pathways that are related to morphology-dependent heterogeneity in the electrochemical and chemical stability of these films. X-ray photoelectron spectroscopy of these electrochemically treated FA-PVSK films shows changes in the average near-surface stoichiometry, which suggests that lead-rich crystal termination planes are the most likely sites for electron trapping and thus nanometer-scale perovskite decomposition.

中文翻译：

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使用光谱电化学和光电子能谱测定甲脒铅钙钛矿薄膜的带边能量和形态依赖性稳定性

我们首次展示了器件相关的甲基溴化铵 (MABr) 掺杂的甲脒三卤化铅钙钛矿 (FA-PVSK) 薄膜的前沿轨道能量学（导带最小值 (CBM) 和价带最大值 (VBM)）可以使用紫外-可见分光电化学进行表征，相对于基于光电子能谱的更传统方法，它提供了一种额外且直接的实验技术来确定能带值。FA-PVSK 薄膜通过两步沉积工艺在半透明的氧化铟锡 (ITO) 和二氧化钛 (TiO2) 电极上进行处理，已知可提供高效太阳能电池。光谱电化学表征在非溶剂电解质中进行，FA-PVSK 吸光度漂白的起始电位用于估计 CBM，它提供了 ca 的值。在 ITO 和 TiO2 电极上，相对于真空 -4.0 eV。由于电子从电极注入钙钛矿，CBM 在掩埋金属氧化物/FA-PVSK 界面处被独特地探测，否则很难表征厚膜。相同 FA-PVSK 薄膜的 UPS 表征提供了 VBM 和电极相关能量的补充近表面测量。除了能量学之外，非溶剂电解质中的受控电化学电荷注入实验揭示了与这些膜的电化学和化学稳定性的形态依赖性异质性相关的分解途径。这些经电化学处理的 FA-PVSK 薄膜的 X 射线光电子能谱显示平均近表面化学计量的变化，