New Variants of (110)‐Oriented Layered Lead Bromide Perovskites, Templated by Formamidinium or Pyrazolium

Abstract

Four new hybrid lead(II) halide perovskites, γ-(FA) 2 PbBr 4 , (FA) 1.5 (AA) 0.5 PbBr 4 , (PY)(GA)PbBr 4 and (PY)(TZ)PbBr 4 ((FA) = formamidinium, (AA) = acetamidinium, (PY) = pyrazolium, (GA) = guanidinium and (TZ) = 1,2,3-triazolium), adopt (110)-oriented layered perovskite structures. While (PY) is found to template the formation of 'conventional' (110)-oriented structure types (i. e. containing staggered [PbBr 4 ] 1 layers), (FA) is shown to facilitate formation of much less common variants based 3 : 1 ordering of the interlayer species or 3 × 2 step-like corrugation of the perovskite-like layers themselves.

Acetamidinium bromoplumbate CH3C(NH2)2PbBr3 with 4H BaRuO3 structure

“…The angles of Br(1)–Pb–Br(1) are largely reduced from 90° indicating strong distortion from the ideal octahedral geometry. Similar octahedral distortion of [PbBr 6 ] 4− was also observed in the 1D Pb–Br network of (ACA) 2 PbBr 4 20,21 …”

“…The hexagonal channels align unobstructed along the c-axis due to absence of the lone octahedral [PbBr 6 ] 4À building unit, which is occupied by half of the total ACA ions as shown in Figure 3. Pb, Br, and ACA have 20,21 The acetamidinium cations were refined anisotropically by applying constrains in the bond lengths and thermal ellipsoids. Although the distances between the C-C and C-N distances are rather distinct (1.314, 1.317, 1.307 Å for C-N and 1.40, 1.45, 1.477 Å for C-C bonds), 22,23 the C-N bond restraints were set to 1.40 (0.05).…”

Crystallization Pathways of FABr-PbBr2-DMF and FABr-PbBr2-DMSO Systems: The Comprehensive Picture of Formamidinium-Based Low-Dimensional Perovskite-Related Phases and Intermediate Solvates

“…There are three layered perovskite-derived phases with the FA 2 PbBr 4 stoichiometry corresponding to different crystal structures. The crystal structures of these polymorphs have already been published earlier [ 19 , 20 ]. The t -FA 2 PbBr 4 and m -FA 2 PbBr 4 compounds crystallize from DMF solution [ 19 ] while γ -FA 2 PbBr 4 forms under distinctly different synthetic conditions precipitating under cooling from concentrated aqueous HBr [ 20 ].…”

“…The crystal structures of these polymorphs have already been published earlier [ 19 , 20 ]. The t -FA 2 PbBr 4 and m -FA 2 PbBr 4 compounds crystallize from DMF solution [ 19 ] while γ -FA 2 PbBr 4 forms under distinctly different synthetic conditions precipitating under cooling from concentrated aqueous HBr [ 20 ]. Two of the FA 2 PbBr 4 polymorphs have the crystal structure of (110)-oriented layered perovskite with ‘2 × 2’ arrangement of the inorganic layers whereas the third polymorph γ -FA 2 PbBr 4 adopts a ‘3 × 2’ arrangement of the inorganic layers (see Figure 1 ).…”

“…Unlike methylammonium and cesium the flat FA + cation is considered to form plenty of layered two-dimensional (2D) polymorphs in the presence of organic halide excess [ 19 , 20 ] which can form multiphase heterostructures with FAPbBr 3 3D perovskite with highly tunable and improved optical properties such as enhanced EQE and reversed photochromism [ 21 , 22 , 23 ] of hybrid materials since it can form phases with different inorganic substructure dimensions (3D and 2D) [ 19 , 20 ]. Additionally, two adducts of formamidinium bromoplumbates with DMSO were recently discovered (FA 2 PbBr 4 ·DMSO and FAPbBr 3 ·DMSO) [ 17 , 24 ].…”