Sarkar Diganta, Stelmakh Andriy, Karmakar Abhoy, Aebli Marcel, Krieg Franziska, Bhattacharya Amit, Pawsey Shane, Kovalenko Maksym V, Michaelis Vladimir K
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1-5, Zurich CH-8093, Switzerland.
ACS Nano. 2024 Aug 20;18(33):21894-21910. doi: 10.1021/acsnano.4c02057. Epub 2024 Aug 7.
Inorganic colloidal cesium lead halide perovskite nanocrystals (NCs) encapsulated by surface capping ligands exhibit tremendous potential in optoelectronic applications, with their surface structure playing a pivotal role in enhancing their photophysical properties. Soy lecithin, a tightly binding zwitterionic surface-capping ligand, has recently facilitated the high-yield synthesis of stable ultraconcentrated and ultradilute colloids of CsPbX NCs, unlocking a myriad of potential device applications. However, the atomic-level understanding of the ligand-terminated surface structure remains uncertain. Herein, we use a versatile solid-state nuclear magnetic resonance (NMR) spectroscopic approach, in combination with dynamic nuclear polarization (DNP) and atomistic molecular dynamics (MD) simulations, to explore the effect of lecithin on the core-to-surface structures of CsPbX (X = Cl or Br) perovskites, sized from micron to nanoscale. Surface-selective (cross-polarization, CP) solid-state and DNP NMR (Cs and Pb) methods were used to differentiate the unique surface and core chemical environments, while the head-groups {trimethylammonium [-N(CH)] and phosphate (-PO)} of lecithin were assigned via H, C, and P NMR spectroscopy. A direct approach to determining the surface structure by capitalizing on the unique heteronuclear dipolar couplings between the lecithin ligand (H and P) and the surface of the CsPbCl NCs (Cs and Pb) is demonstrated. The H-Cs heteronuclear correlation (HETCOR) DNP NMR indicates an abundance of Cs on the NC surface and an intimate proximity of the -N(CH) groups to the surface and subsurface Cs atoms, supported by H{Cs} rotational-echo double-resonance (REDOR) NMR spectroscopy. Moreover, the H-P{Pb} CP REDOR dephasing curve provides average internuclear distance information that allows assessment of -PO groups binding to the subsurface Pb atoms. Atomistic MD simulations of ligand-capped CsPbCl surfaces aid in the interpretation of this information and suggest that ligand -N(CH) and -PO head-groups substitute Cs and Cl ions, respectively, at the CsCl-terminated surface of the NCs. These detailed atomistic insights into surface structures can further guide the engineering of various relevant surface-capping zwitterionic ligands for diverse metal halide perovskite NCs.
由表面封端配体包裹的无机胶体铯铅卤化物钙钛矿纳米晶体（NCs）在光电子应用中展现出巨大潜力，其表面结构在增强光物理性质方面起着关键作用。大豆卵磷脂是一种紧密结合的两性离子表面封端配体，最近它促进了CsPbX NCs稳定的超高浓度和超低浓度胶体的高产率合成，开启了众多潜在的器件应用。然而，对配体终止的表面结构的原子级理解仍不明确。在此，我们使用一种通用的固态核磁共振（NMR）光谱方法，结合动态核极化（DNP）和原子分子动力学（MD）模拟，来探究卵磷脂对从微米到纳米尺度的CsPbX（X = Cl或Br）钙钛矿的核到表面结构的影响。表面选择性（交叉极化，CP）固态和DNP NMR（Cs和Pb）方法用于区分独特的表面和核心化学环境，而卵磷脂的头基{三甲基铵[-N(CH)]和磷酸根(-PO)}通过H、C和P NMR光谱进行归属。展示了一种利用卵磷脂配体（H和P）与CsPbCl NCs表面（Cs和Pb）之间独特的异核偶极耦合来确定表面结构的直接方法。H-Cs异核相关（HETCOR）DNP NMR表明NC表面存在大量Cs，并且-N(CH)基团与表面和次表面Cs原子紧密相邻，这得到了H{Cs}旋转回波双共振（REDOR）NMR光谱的支持。此外，H-P{Pb} CP REDOR去相位曲线提供了平均核间距信息，可用于评估-PO基团与次表面Pb原子的结合情况。配体封端的CsPbCl表面的原子MD模拟有助于解释这些信息，并表明配体-N(CH)和-PO头基分别在NCs的CsCl终止表面取代Cs和Cl离子。这些对表面结构的详细原子见解可进一步指导为各种金属卤化物钙钛矿NCs设计各种相关的表面封端两性离子配体。
