The Tetrel Bond and Tetrel Halide Perovskite Semiconductors

Abstract

The ion pairs [Cs+•TtX3−] (Tt = Pb, Sn, Ge; X = I, Br, Cl) are the building blocks of all-inorganic cesium tetrel halide perovskites in 3D, CsTtX3, that are widely regarded as blockbuster materials for optoelectronic applications such as in solar cells. The 3D structures consist of an anionic inorganic tetrel halide framework stabilized by the cesium cations (Cs+). We use computational methods to show that the geometrical connectivity between the inorganic monoanions, [TtX3−]∞, that leads to the formation of the TtX64− octahedra and the 3D inorganic perovskite architecture is the result of the joint effect of polarization and coulombic forces driven by alkali and tetrel bonds. Depending on the nature and temperature phase of these perovskite systems, the Tt···X tetrel bonds are either indistinguishable or somehow distinguishable from Tt–X coordinate bonds. The calculation of the potential on the electrostatic surface of the Tt atom in molecular [Cs+•TtX3−] provides physical insight into why the negative anions [TtX3−] attract each other when in close proximity, leading to the formation of the CsTtX3 tetrel halide perovskites in the solid state. The inter-molecular (and inter-ionic) geometries, binding energies, and charge density-based topological properties of sixteen [Cs+•TtX3−] ion pairs, as well as some selected oligomers [Cs+•PbI3−]n (n = 2, 3, 4), are discussed.

Methylammonium Tetrel Halide Perovskite Ion Pairs and Their Dimers: The Interplay between the Hydrogen-, Pnictogen- and Tetrel-Bonding Interactions

“…Metal halide perovskite semiconductors are an important class of hybrid chemical systems [ 1 , 2 , 3 ]. They have been synthesized as either organic–inorganic hybrid perovskites [ 4 , 5 , 6 ] or all-inorganic perovskites [ 7 , 8 , 9 ]. Compounds of the first type have often been referred to as organometallic halide perovskites [ 10 , 11 , 12 ].…”

“…In organic–inorganic hybrid perovskites [ 4 , 5 , 6 ], the organic cation couples with the inorganic anion to form an ion pair [ 20 , 21 , 22 , 23 , 24 ]; applying periodic boundary conditions leads to the formation of a bulk material [ 25 , 26 ]. In the case of all-inorganic perovskites, an inorganic cation couples with another inorganic anion to form an ion pair [ 9 , 20 ]. Both types of metal-based halide perovskites have been synthesized as crystalline materials in a variety of dimensions (i.e., 0D, 1D, 2D and 3D) [ 27 , 28 , 29 , 30 ].…”

“…Similar views have been provided on the interionic intermolecular interactions that act as the glue that holds the organic and inorganic materials together in organic–inorganic hybrid materials. The importance of organic cations as additives in organic–inorganic halide perovskites has been demonstrated [ 65 , 66 ], but there seems to be some controversy concerning the role they play in triggering their optoelectronic properties [ 9 , 19 , 21 , 67 , 68 , 69 ].…”

“…A point of much discussion is the nature of the chemical bonding in organic–inorganic hybrids, for example, in FAPbI 3 [ 70 ] and MATtX 3 (Tt = Pb; X = I, Br) [ 9 , 22 , 23 , 71 , 72 , 73 ]. Contrary to views that there is no hydrogen bonding in hybrid lead halide perovskites at room temperature [ 74 ], which is curious given that these systems have no geometric stability without the intermolecular interactions, we and others have stressed that the N–H···X hydrogen bonds hold the ion pairs MA CH 3 NH 3 + ) and TtX 3 − together in a well-defined structure of organic–inorganic hybrids, both in the low-temperature (orthorhombic [ 22 , 75 , 76 ]) and the room-temperature (tetragonal [ 23 , 77 ]) phases.…”

“…The C–N···X pnictogen bonds are non-negligible contributors to the tilting of the TtX 6 4− octahedra of the low-temperature orthorhombic phase ( Figure 1 c) and the X–Tt···X tetrel bonds are the key geometric players in the formation of the TtX 6 4− octahedra and the resultant cage-like structure that hosts the organic cation (see polyhedral models in Figure 1 a–c). The definition and characteristic features of the hydrogen bond [ 78 ], pnictogen bond [ 79 , 80 ] and tetrel bond [ 9 , 81 , 82 ] have been discussed elsewhere, which we outline in a following section, and a discussion of the physical chemistry of charge-assisted non-covalent interactions can be found elsewhere [ 82 , 83 , 84 , 85 , 86 ]. We utilize Density Functional Theory (DFT) calculations at the ω B97X-D [ 87 ] level of theory, together with the Quantum Theory of Atoms in Molecules (QTAIM) [ 88 ], Molecular Electrostatic Surface Potential (MESP) [ 89 , 90 , 91 , 92 ] and Independent Gradient Model (IGM) [ 93 , 94 ] approaches, to validate our conclusions.…”