Preferred orientations of organic cations at lead-halide perovskite interfaces revealed using vibrational sum-frequency spectroscopy

Sung, Woongmo; Müller, Christian; Hietzschold, Sebastian; Lovrinčić, Robert; Gallop, Nathaniel P.; Bakulin, Artem A.; Nihonyanagi, Satoshi; Tahara, Tahei

doi:10.1039/c9mh01394f

Cited by 17 publications

(13 citation statements)

References 59 publications

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“…Such selection rules make SFG show powerful potential in the research of nanomaterials. In fact, SFG has been applied to probe molecular conformation of the organic cations of lead-halide perovskite 23 , 56 and the capping ligands on nanoparticle surfaces 24 , 25 , 30 .…”

Section: Resultsmentioning

confidence: 99%

Conformational disorder of organic cations tunes the charge carrier mobility in two-dimensional organic-inorganic perovskites

Jin

et al. 2020

Nat Commun

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The chemical nature of the organic cations governs the optoelectronic properties of two-dimensional organic-inorganic perovskites. But its mechanism is not fully understood. Here, we apply femtosecond broadband sum frequency generation vibrational spectroscopy to investigate the molecular conformation of spacer organic cations in two-dimensional organic-inorganic perovskite films and establish a correlation among the conformation of the organic cations, the charge carrier mobility, and broadband emission. Our study indicates that both the mobility and broadband emission show strong dependence on the molecular conformational order of organic cations. The gauche defect and local chain distortion of organic cations are the structural origin of the in-plane mobility reduction and broad emission in two-dimensional organic-inorganic perovskites. Both of the interlayer distance and the conformational order of the organic cations affect the out-of-plane mobility. This work provides molecular-level understanding of the conformation of organic cations in optimizing the optoelectronic properties of two-dimensional organic-inorganic perovskites.

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Section: Resultsmentioning

confidence: 99%

Conformational disorder of organic cations tunes the charge carrier mobility in two-dimensional organic-inorganic perovskites

Jin

et al. 2020

Nat Commun

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“…A Cs ion is spherical, so it does not break the crystallographic centrosymmetry of the system, so it is isotropic. In contrast, the MA cation is anisotropic and polar, so it can break the crystallographic symmetry of Pm m and induce polarization in the system if specific alignments of MA cations are assumed. − Although it is reported that the MA cation in hybrid perovskite is in a rotationally disordered state at room temperature due to thermal motion of the cation, some evidence suggests that lattice distortions and local field effects permit preferential orientation of the MA cation at interfaces . For the study, we first determined the MA orientation in cubic MASnBr 3 .…”

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confidence: 99%

“…23−25 Although it is reported that the MA cation in hybrid perovskite is in a rotationally disordered state at room temperature due to thermal motion of the cation, 26 some evidence suggests that lattice distortions and local field effects permit preferential orientation of the MA cation at interfaces. 27 For the study, we first determined the MA orientation in cubic MASnBr 3 . Among different MA configurations, an MA cation placed along the diagonal of the cube is most energetically stable (Figure S1); this result agrees with a previous result.…”

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confidence: 99%

A-Site Effect on the Oxidation Process of Sn-Halide Perovskite: First-Principles Calculations

Kim

Lee

Kim

et al. 2021

J. Phys. Chem. Lett.

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Tin-halide perovskite solar cells (Sn-PSCs) are promising candidates as an alternative to toxic lead-halide PSCs. However, Sn2+ is easily oxidized to Sn4+, so Sn-PSCs are unstable in air. Here, we use first-principles density functional theory calculations to elucidate the oxidation process of Sn2+ at the surface of ASnBr3 [A = Cs or CH3NH3 (MA)]. Regardless of the A-site cation, adsorption of O2 leads to the formation of SnO2, which creates a Sn vacancy at the surface. The A-site cation determines whether the created vacancies are stabilized in the bulk or at the surface. For CsSnBr3, the Sn vacancy is stabilized at the surface, so further oxidation is limited. For MASnBr3, the Sn vacancy moves into bulk region, so additional Sn is supplied to the surface; as a result, a continuous oxidation process can occur. The stabilization of Sn vacancy is closely related to the polarization that the A-site cation causes in the system.

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“…VSFG employs a broadband IR pulse (290 fs duration) centered at ~2850 cm -1 to excite CH vibrational modes of the SDS@2β-CD system, which is followed by a narrowband 1025nm near IR pulse to upcovert the vibrational coherence to a higher frequency macroscopic polarization emitted as the VSFG signal. As an even-order nonlinear optical process, only noncentrosymmetric systems produce VSFG responses, such as the air/liquid, air/solid and solid/liquid interfaces 29,31,[40][41][42][32][33][34][35][36][37][38][39] with a powerful demonstration of the techniques capabilities found in its application to the air/water interface. [43][44][45] Another class of systems that can be studied by VSFG that have not been paid much attention are materials without inversion centers.…”

Section: Linescanning Vsfg Imagingmentioning

confidence: 99%

Imaging Orientation of a Single Molecular Hierarchical Self-Assembled Sheet: The Combined Power of a Vibrational Sum Frequency Generation Microscopy and Neural Network

Wagner

Xiong

2022

Preprint

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In this work, we determined the tilt angles of molecular units in hierarchical self-assembled materials on a single-sheet level, which were not available previously. This was achieved by developing a fast linescanning vibrational sum frequency generation (VSFG) hyperspectral imaging technique in combination with neural network analysis. Rapid VSFG imaging enables polarization resolved images on a single sheet level to be measured within a short time period, circumventing technical challenges due to long term optical setup instability. The polarization resolved hyperspectral images were then used to extract the supramolecular tilt angle of a self-assembly through a set of spectra-tilt angle relationships which were solved through neural network techniques. This unique combination of both novel techniques offers a new pathway to resolve molecular level structural knowledge of self-assembled materials. Understanding these properties can further drive self-assembly design from a bottom-up approach for applications in biomimetic and drug delivery researches.

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Preferred orientations of organic cations at lead-halide perovskite interfaces revealed using vibrational sum-frequency spectroscopy

Abstract: Using vibrational sum frequency generation (VSFG) spectroscopy, we investigate the behaviour of organic cations at the surface of a series of multilayer lead halide perovskite systems, finding that the behaviour of the organic cations changes dramatically close to the interface.

Cited by 17 publications

References 59 publications

Conformational disorder of organic cations tunes the charge carrier mobility in two-dimensional organic-inorganic perovskites

Conformational disorder of organic cations tunes the charge carrier mobility in two-dimensional organic-inorganic perovskites

A-Site Effect on the Oxidation Process of Sn-Halide Perovskite: First-Principles Calculations

Imaging Orientation of a Single Molecular Hierarchical Self-Assembled Sheet: The Combined Power of a Vibrational Sum Frequency Generation Microscopy and Neural Network

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