Nanoscale Phase Segregation in Supramolecular π-Templating for Hybrid Perovskite Photovoltaics from NMR Crystallography

Abstract

The use of layered perovskites is an important strategy to improve the stability of hybrid perovskite materials and their optoelectronic devices. However, tailoring their properties requires accurate structure determination at the atomic scale, which is a challenge for conventional diffraction-based techniques. We demonstrate the use of nuclear magnetic resonance (NMR) crystallography in determining the structure of layered hybrid perovskites for a mixed-spacer model composed of 2-phenylethylammonium (PEA + ) and 2-(perfluorophenyl)ethylammonium (FEA + ) moieties, revealing nanoscale phase segregation. Moreover, we illustrate the application of this structure in perovskite solar cells with power conversion efficiencies that exceed 21%, accompanied by enhanced operational stability.

Interfaces in metal halide perovskites probed by solid-state NMR spectroscopy

“…2b). [231][232][233][234] During polycrystalline lm growth, phase segregation between regions with different 2D connement indices (the n value from the formula unit R 2 A nÀ1 B n X 3n+1 ) can occur. Layered MHPs with a nominal stoichiometry of n greater than 2 typically segregate into regions of higher and lower n-values due to solution-processing kinetics.…”

“…ssNMR spectroscopy is a powerful characterization tool to understand the local molecular structures of spacer cations, and their interactions with A sites and X sites within the perovskite slabs. 232,309,374,375 One notable example is the use of 1 H- 207 Pb heteronuclear correlation NMR to gain insights into the octahedral structures of 2D BA 2 MA nÀ1 Pb n I 3n+1 (n ¼ 1 to n ¼ 4, a value determining the thickness of the lead halide octahedral layer) Ruddlesden-Fig. 9 Layer-by-layer identification of 2D RP phases: 2D 1 H-detected 207 Popper phases with butylammonium (BA) spacers (Fig.…”

“…10 Protocols that combine ssNMR spectroscopy, X-ray scattering and modelling approaches (i.e., NMR crystallography) have been employed to characterize the structures and intermolecular interactions in MHPs and other perovskite materials. 232,376 Development of such integrated methods are important to understand the chemical nature of mixed spacer cations in layered MHPs at the atomic scale, which is a challenge for conventional diffraction-based techniques or ssNMR spectroscopy alone. Hope et al applied an NMR crystallography approach to elucidate the supramolecular structure of the mixed cation organic spacers in layered hybrid perovskites.…”

“…Hope et al applied an NMR crystallography approach to elucidate the supramolecular structure of the mixed cation organic spacers in layered hybrid perovskites. 232 By using this approach, 3D structures of layered hybrid perovskites consisting of 2-phenylethylammonium (PEA + ) and 2-(per-uorophenyl)ethylammonium (FEA + ) moieties have been proposed. This study revealed that the spacer cations in a mixed arene-uoroarene model system most closely resemble those of phase-segregated PEA + /FEA + compositions, rather than a solid solution (Fig.…”

Direct Investigation of the Reorientational Dynamics of A-site Cations in 2D Organic-Inorganic Hybrid Perovskite by Solid-State NMR

“…Recently, another new class of two-dimensional organic-inorganic hybrid perovskites (2D OIHPs) have attracted great attention owing to their superior ambient stability, as well as their promising optoelectronic properties [21][22][23][24] . Ruddlesden-Popper perovskites (RPPs) are typical examples of this class of layered 2D organic-inorganic hybrid perovskites (2D OIHPs), having the generic chemical formula A′ 2 A n−1 M n X 3n+1 , where A′ represents an organic spacer, such as long chain alkylammonium cation (1butylammonium, BA + ) or phenyl alkylammonium cation (2-phenethylammonium, PEA + ), A is an organic cation, M is a metal, X is a halide, and n is the number of octahedral slabs per unit cell [25][26][27][28] .…”