Preferred orientations of organic cations at lead-halide perovskite interfaces revealed using vibrational sum-frequency spectroscopy
Preferred orientations of organic cations at lead-halide perovskite interfaces revealed using vibrational sum-frequency spectroscopy
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DOI：
10.1039/c9mh01394f
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发表时间：
2020-05
影响因子：
13.3
通讯作者：
Woongmo Sung;C. Müller;S. Hietzschold;R. Lovrinčić;Nathaniel P. Gallop;A. Bakulin;S. Nihonyanagi;T. Tahara
中科院分区：
文献类型：
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作者：
Woongmo Sung;C. Müller;S. Hietzschold;R. Lovrinčić;Nathaniel P. Gallop;A. Bakulin;S. Nihonyanagi;T. Tahara
卤化铅钙钛矿的界面层的结构预计将在载流子动力学和基于钙钛矿的器件的性能中起关键作用。然而，在分子水平上对钙钛矿界面的结构和动力学知之甚少。在这项研究中，我们通过监测甲基铵（MA）溴化铅钙钛矿中阳离子的排列来访问钙钛矿界面的分子动力学。为此，我们应用外差检测的振动和频产生（HD-VSFG）光谱与DFT计算的帮助下，一系列的薄膜钙钛矿活性层与几种有机和氧化物半导体材料的接口。在与空气，玻璃，TiO 2和NiO传输层和苯基-C61-丁酸甲酯（PCBM）的界面处，我们没有观察到阳离子振动的特征，表明阳离子的随机排列。另一方面，2，2 ′，7，7 ′-四[N，N-二（4-甲氧基苯基）氨基]-9，9 ′-螺二芴（Spiro-MeOH 4）/钙钛矿界面的HD-VSFG光谱显示出对应于铵反对称弯曲模式的清晰峰，表明MA的铵部分优先朝向Spiro-MeOH 4层取向，大部分MA阳离子远离表面法线倾斜。所观察到的界面各向异性是在对比与一般图片接受散装钙钛矿材料。我们讨论了在钙钛矿太阳能电池内的各种界面处的局部场和载流子注入的背景下所观察到的现象的潜在后果。
The structure of the interfacial layers of lead halide perovskites is expected to play a crucial role in carrier dynamics and in the performance of perovskite-based devices. However, little is known about the structure and dynamics of perovskite interfaces at the molecular level. In this study, we access molecular dynamics at perovskite interfaces by monitoring the alignment of cations in methylammonium (MA) lead bromide perovskite. For this we apply heterodyne-detected vibrational sum-frequency generation (HD-VSFG) spectroscopy with the help of DFT calculations to a range of thin-film perovskite active layers interfaced with several organic and oxide semiconducting materials. At interfaces with air, glass, TiO2 and NiO transport layers and phenyl-C61-butyric acid methyl ester (PCBM), we observed no signature of cation vibrations, indicating a randomized arrangement of cations. On the other hand, HD-VSFG spectra of 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-MeOTAD)/perovskite interfaces exhibited a clear peak corresponding to the ammonium antisymmetric bending mode, indicating that the MA's ammonium moiety is preferentially oriented towards the Spiro-MeOTAD layer with a large portion of MA cations are tilted away from the surface normal. The observed interfacial anisotropy is in contrast with the general picture accepted for bulk perovskite materials. We discuss the potential consequences of the observed phenomena in the context of the local field and carrier injection at the various interfaces within the perovskite solar cells.