Researchers from Duke University, University of Colorado - Boulder, Israel's Weizmann Institute of Science, Polish Academy of Sciences and University of Lille CNRS have examined the local structure of halide perovskites in their molten and glassy states, revealing the critical connection between these structures and the contrasting properties observed in their crystalline vs glassy states.
The findings of this work enhance scientists' understanding of the diverse structural motifs in perovskites and how structural changes in perovskite glass impact their properties, paving the way for advancements in next-generation phase change materials and devices.
In an earlier study from 2020, the Duke team sought to gain better understanding of glassy halide perovskites - somewhat of a departure from the traditionally studied crystalline halide perovskites. Since 2021, their work has inspired interest, resulting in the establishment of a novel research domain centered around glass-forming hybrid perovskite semiconductors and related glassy hybrid metal halides.
In this recent work, the team made use of a combination of Raman spectroscopy, solid-state nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy, in situ X-ray diffraction (XRD) and pair distribution function (PDF) analysis to investigate the coordination environment in crystalline, glass and melt states of the 2D MHP [(S)-(−)-1-(1-naphthyl)ethylammonium]2PbBr4.
While crystalline SNPB shows polarization-dependent Raman spectra, the glassy and melt states exhibit broad features and lack polarization dependence. Solid-state NMR reveals disordering at the organic−inorganic interface of the glass due to significant spatial disruption in the tethering ammonium groups and the corresponding dihedral bond angles connecting the naphthyl and ammonium groups, while still preserving substantial naphthyl group registry and remnants of the layering from the crystalline state (deduced from XRD analysis). Moreover, PDF analysis demonstrates the persistence of corner-sharing PbBr6 octahedra in the inorganic framework of the melt/glass phases, but with a loss of structural coherence over length scales exceeding approximately one octahedron due to disorder in the inter- and intraoctahedra bond angles/lengths.
This study represents the first comparison of the local structure within a molten and glassy MHP (relative to the crystalline state), achieved through a comprehensive integration of Raman spectroscopy, solid-state NMR, FTIR, and XRD coupled with PDF measurements. These findings aid in comprehending the structural distinctions among different states of MHPs and shed light on the structure induced property changes that can be leveraged in the development of next generation energy storage, memory and computing devices.
