Abstract:Hybrid perovskite crystals with organic and inorganic structural components are able to combine desirable properties from both classes of materials. Electronic interactions between the anionic inorganic framework and functional organic cations (such as chromophores or semiconductors) can give rise to unusual photophysical properties. Cyanine dyes are a well known class of cationic organic dyes with high extinction coefficients and tunable absorption maxima all over the visible and near-infrared spectrum. Here … Show more
“…Their configurations can be either linear or zigzag, and their chemical formulae are variable depending on the connecting methods and the organic cations chosen 224 . Although many recent examples of this are available 225–227 , we note in particular that CsPbI 3 adopts a distorted nanowire-like structure in one dimension that unambiguously does not involve H-bonding 228 .Figure 12The orthorhombic ( Pmna ) geometry of WO 3 , showing a perovskite-like architecture without the presence of any B-site cation inside the cage. The tilting angles and lattice constants are shown.…”
The CH3NH3PbI3 (methylammonium lead triiodide) perovskite semiconductor system has been viewed as a blockbuster research material during the last five years. Because of its complicated architecture, several of its technological, physical and geometrical issues have been examined many times. Yet this has not assisted in overcoming a number of problems in the field nor in enabling the material to be marketed. For instance, these studies have not clarified the nature and type of hydrogen bonding and other noncovalent interactions involved; the origin of hysteresis; the actual role of the methylammonium cation; the nature of polarity associated with the tetragonal geometry; the unusual origin of various frontier orbital contributions to the conduction band minimum; the underlying phenomena of spin-orbit coupling that causes significant bandgap reduction; and the nature of direct-to-indirect bandgap transition features. Arising from many recent reports, it is now a common belief that the I···H–N interaction formed between the inorganic framework and the ammonium group of CH3NH3+ is the only hydrogen bonded interaction responsible for all temperature-dependent geometrical polymorphs of the system, including the most stable one that persists at low-temperatures, and the significance of all other noncovalent interactions has been overlooked. This study focussed only on the low temperature orthorhombic polymorph of CH3NH3PbI3 and CD3ND3PbI3, where D refers deuterium. Together with QTAIM, DORI and RDG based charge density analyses, the results of density functional theory calculations with PBE with and without van der Waals corrections demonstrate that the prevailing view of hydrogen bonding in CH3NH3PbI3 is misleading as it does not alone determine the a−b+a− tilting pattern of the PbI64− octahedra. This study suggests that it is not only the I···H/D–N, but also the I···H/D–C hydrogen/deuterium bonding and other noncovalent interactions (viz. tetrel-, pnictogen- and lump-hole bonding interactions) that are ubiquitous in the orthorhombic CH3NH3PbI3/CD3ND3PbI3 perovskite geometry. Their interplay determines the overall geometry of the polymorph, and are therefore responsible in part for the emergence of the functional optical properties of this material. This study also suggests that these interactions should not be regarded as the sole determinants of octahedral tilting since lattice dynamics is known to play a critical role as well, a common feature in many inorganic perovskites both in the presence and the absence of the encaged cation, as in CsPbI3/WO3 perovskites, for example.
“…Their configurations can be either linear or zigzag, and their chemical formulae are variable depending on the connecting methods and the organic cations chosen 224 . Although many recent examples of this are available 225–227 , we note in particular that CsPbI 3 adopts a distorted nanowire-like structure in one dimension that unambiguously does not involve H-bonding 228 .Figure 12The orthorhombic ( Pmna ) geometry of WO 3 , showing a perovskite-like architecture without the presence of any B-site cation inside the cage. The tilting angles and lattice constants are shown.…”
The CH3NH3PbI3 (methylammonium lead triiodide) perovskite semiconductor system has been viewed as a blockbuster research material during the last five years. Because of its complicated architecture, several of its technological, physical and geometrical issues have been examined many times. Yet this has not assisted in overcoming a number of problems in the field nor in enabling the material to be marketed. For instance, these studies have not clarified the nature and type of hydrogen bonding and other noncovalent interactions involved; the origin of hysteresis; the actual role of the methylammonium cation; the nature of polarity associated with the tetragonal geometry; the unusual origin of various frontier orbital contributions to the conduction band minimum; the underlying phenomena of spin-orbit coupling that causes significant bandgap reduction; and the nature of direct-to-indirect bandgap transition features. Arising from many recent reports, it is now a common belief that the I···H–N interaction formed between the inorganic framework and the ammonium group of CH3NH3+ is the only hydrogen bonded interaction responsible for all temperature-dependent geometrical polymorphs of the system, including the most stable one that persists at low-temperatures, and the significance of all other noncovalent interactions has been overlooked. This study focussed only on the low temperature orthorhombic polymorph of CH3NH3PbI3 and CD3ND3PbI3, where D refers deuterium. Together with QTAIM, DORI and RDG based charge density analyses, the results of density functional theory calculations with PBE with and without van der Waals corrections demonstrate that the prevailing view of hydrogen bonding in CH3NH3PbI3 is misleading as it does not alone determine the a−b+a− tilting pattern of the PbI64− octahedra. This study suggests that it is not only the I···H/D–N, but also the I···H/D–C hydrogen/deuterium bonding and other noncovalent interactions (viz. tetrel-, pnictogen- and lump-hole bonding interactions) that are ubiquitous in the orthorhombic CH3NH3PbI3/CD3ND3PbI3 perovskite geometry. Their interplay determines the overall geometry of the polymorph, and are therefore responsible in part for the emergence of the functional optical properties of this material. This study also suggests that these interactions should not be regarded as the sole determinants of octahedral tilting since lattice dynamics is known to play a critical role as well, a common feature in many inorganic perovskites both in the presence and the absence of the encaged cation, as in CsPbI3/WO3 perovskites, for example.
“…Although the properties of these materials are intriguing, a major challenge complicating the study of ''complex-organic perovskites'' (COPs) is thin film deposition. Most investigations into the properties of perovskites or related hybrids incorporating truly large cations, particularly those large enough for the organic singlet state to lie within the inorganic band gap and exhibit fluorescence, 20,21,26,27 resort to single crystals or powders. However, bulk samples are often inadequate for sensitive and powerful techniques such as transient absorption spectroscopy (TAS), which can provide a wealth of information about excited state dynamics, but require films thin enough to provide a meaningful signal.…”
“…These analyses have allowed to estimate for HP1 a composition of PbI2.510.5. This composition does not agree with the expected formula for 3D, 2D or 1D hybrid lead perovskites that are PbI3X, [31][32] PbI4X2, [33][34] and PbI3X (facetsharing), [35][36] respectively (in which X represents the organic ammonium cation). It could be that the defects on the structure are responsible for the deviation of the empirical formula from the ideal composition expected for these 2D materials.…”
A hybrid lead iodide material (HP1) having 4-vinylphenylene ammonium as the organic cation allows post-synthetic modification by radical copolymerization with styrene.
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