Mitigating Measurement Artifacts in TOF-SIMS Analysis of Perovskite Solar Cells
Mitigating Measurement Artifacts in TOF-SIMS Analysis of Perovskite Solar Cells
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DOI：
10.1021/acsami.9b09445
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发表时间：
2019-08-28
影响因子：
9.5
通讯作者：
Berry, Joseph J.
中科院分区：
文献类型：
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作者：
Harvey, Steven P.;Zhang, Fei;Berry, Joseph J.
飞行时间二次离子质谱法（TOF-SIMS）是为数不多的能够明确区分有机阳离子（如甲基铵和甲脒）的技术之一。区分这两种物质可以导致对卤化物钙钛矿太阳能电池中成分不均匀性和化学梯度的起源和演变的具体见解，这似乎是推进该技术的关键。TOF-SIMS可以从混合有机-无机钙钛矿太阳能电池（PSCs）中获得三维的化学信息，而不是简单地将有机成分分解成它们的分子成分（甲基铵和甲脒的C， H和N），这与其他表征方法不同。在这里，我们报告了在对PSC薄膜进行TOF-SIMS深度剖析时测量到的明显普遍存在的a位有机阳离子梯度。利用热机械方法在埋藏的玻璃/透明导电氧化物界面处切割钙钛矿样品，可以实现与常规深度剖面相反方向的深度剖面（背面深度剖面）。当将背面深度剖面与传统的正面剖面进行比较时，在每种情况下都观察到a位有机阳离子信号的轻微梯度相同。这表明，明显的a位阳离子梯度是一个测量伪影，由于原离子束的束损伤导致甲基铵和甲脒的二次离子的离子产量不断下降。这是由于在数据密度过高的情况下，30 keV的铋初级离子束撞击会造成亚表面注入和键断裂。在这里，我们展示了与这种损害相关的波束产生的伪影可以通过改变测量条件来减轻。我们还报道了一种应用于PSC薄膜的深度剖面的新方法，该方法可以增强对正测量极性的卤化物离子的灵敏度，从而在大多数情况下可以消除对负极性的第二次测量的需要。
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is one of the few techniques that can specifically distinguish between organic cations such as methylammonium and formamidinium. Distinguishing between these two species can lead to specific insight into the origins and evolution of compositional inhomogeneity and chemical gradients in halide perovskite solar cells, which appears to be a key to advancing the technology. TOF-SIMS can obtain chemical information from hybrid organic- inorganic perovskite solar cells (PSCs) in up to three dimensions, while not simply splitting the organic components into their molecular constituents (C, H, and N for both methylammonium and formamidinium), unlike other characterization methods. Here, we report on the apparently ubiquitous A-site organic cation gradient measured when doing TOF-SIMS depth-profiling of PSC films. Using thermomechanical methods to cleave perovskite samples at the buried glass/transparent conducting oxide interface enables depth profiling in a reverse direction from normal depth profiling (backside depth profiling). When comparing the backside depth profiles to the traditional front side profiled devices, an identical slight gradient in the A-site organic cation signal is observed in each case. This indicates that the apparent A-site cation gradient is a measurement artifact due to beam damage from the primary ion beam causing a continually decreasing ion yield for secondary ions of methylammonium and formamidinium. This is due to subsurface implantation and bond breaking from the 30 keV bismuth primary ion beam impact when profiling with too high of a data density. Here, we show that the beam-generated artifact associated with this damage can mostly be mitigated by altering the measurement conditions. We also report on a new method of depth profiling applied to PSC films that enables enhanced sensitivity to halide ions in positive measurement polarity, which can eliminate the need for a second measurement in negative polarity in most cases.