Polymorphism in metal halide perovskites

Abstract

Metal halide perovskites (MHPs) are frontrunners among solution-processable materials for lightweight, large-area and flexible optoelectronics. These materials, with the general chemical formula AMX3, are structurally complex, undergoing multiple polymorph transitions...

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

“…Polymorphism in MHPs is well-documented across different temperatures and pressures. 55 MHP phase transformations are oen displacive, without any bonds forming or breaking. As a result, the interfaces that form during displacive transformations are more like the bulk chemical environment than during reconstructive transformations.…”

“…4a), which can be separately excited and detected. The MHPs and the contact layers contain several NMR active nuclei: 1 H, 7 Li, 11 B, 13 C, 14 N, 15 N, 19 F, 27 Al, 33 S, 35 Cl, 37 Cl, 39 K, 41 K, 49 Ti, 55 Mn, 63 Cu, 65 Cu, 67 Zn, 73 Ge, 79 Br, 81 Br, 85 Rb, 87 Rb, 107 Ag, 109 Ag, 113 Cd, 119 Sn, 121 Sb, 123 Sb, 123 Te, 125 Te, 127 I, 133 Cs, 207 Pb, and 209 Bi. A wide variety of NMR interactions such as chemical shi (characterized by chemical shi anisotropy, CSA), dipole-dipole couplings, quadrupolar interactions, knight shis, hyperne interactions and paramagnet-induced interactions can be used to characterize local bonding environments and inter-and intramolecular interactions at the sub-nanometer to nanometer length scales.…”

“…CSA scales linearly with B 0 , whereas quadrupolar interaction is inversely proportional to B 0 . In this respect, a combination of high B 0 and fast MAS are expected to help to enhance the resolution in the NMR spectra of quadrupolar nuclei ( 11 B, 14 N, 27 Al, 33 S, 35 Cl, 37 Cl, 39 K, 41 K, 49 Ti, 55 Mn, 63 Cu, 65 Cu, 67 Zn, 73 Ge, 79 Br, 81 Br, 85 Rb, 87 Rb, 121 Sb, 123 Sb, 127 I, 133 Cs and 209 Bi), and the resolution in 207 Pb and 119 Sn NMR spectra can be improved using fast MAS at relatively low B 0 .…”

“…44,45 The defect tolerance of lead halide perovskites has enabled the manufacture of high-performance devices through a variety of scalable solution-phase processes, [46][47][48][49][50][51] solidphase mechanochemical syntheses, 52,53 and vapor-phase approaches. 54 MHPs have relatively low formation energies and exhibit low-temperature phase transformations 55 compared to other semiconductors for optoelectronic applications. The substantially ionic character of bonds in MHPs renders them simple to form but also quick to degrade.…”

Dynamics & Spectroscopy with Neutrons—Recent Developments & Emerging Opportunities

“…Among the OHPs studied to date, the ones containing methylammonium (MA + ) and formamidinium (FA + ) moieties confined in iodo- and bromoplumbate frameworks are the most archetypal ones, and as such they will be used as a guide for further discussion below. This hybrid organic-inorganic chemical composition also translates into an unusual softness and flexibility, which gives rise to a rich polymorphism [ 71 ]. In terms of elastic properties, Figure 2 serves to illustrate where OHPs sit relative to other classes of materials [ 72 , 73 ], essentially at the cross-roads between the ‘ soft ’ and ‘ hard ’ worlds, and comparable to typical polymer or macromolecular systems of an organic nature.…”