Dipolar Materials Research Articles

Dipolar Interlayers in Perovskite Solar Cells

A typical perovskite solar cell (PSC) is composed of a perovskite layer, electron/hole transport layer(s), cathode, and anode, producing several interfaces between these functional layers. These interfaces undoubtedly have great influence on the device performance. Introducing the dipolar interlayer is one of the most significant interface engineering strategies in PSCs, which helps to improve the charge extraction and collection and has made critical contribution to the fast development of PSC technology. Herein, the progress in the use of dipolar interlayers to promote the performance of PSCs is summarized. The dipolar interlayers in PSCs based on the device structure are categorized and the effect of each type of dipolar interlayer on the interface energy‐level structure, interface charge transport and recombination, the interface defect passivation, perovskite morphology, and the device performance is discussed. A perspective on how to develop more effective dipolar interlayer materials and further enhancing the device performance from the viewpoint of the interface and dipolar interlayers is given.

Spin-ice behavior of mixed pyrochlore Dy2GaSbO7 exhibiting enhanced Pauling zero-point entropy

Herein, the low-temperature magnetothermal properties and spin-ice physics of a mixed pyrochlore, Dy2GaSbO7 (DGS), are investigated through dc magnetization, ac susceptibility, and heat capacity experiments, and crystal-field computation. A Curie-Weiss (CW) fit to the dc susceptibility data yields effective magnetic moment, μeff = 10.0 μB/Dy3+ and CW temperature, θCW = +1.62 K. Magnetization attains a saturation value of Msat = 5.06μB/Dy above H ≈ 8 T and at T = 2 K, which is half of the μeff due to the effective Ising-type anisotropy along local 〈111〉 axes of the elementary Dy4O′ tetrahedron, illustrating DGS as an effective spinS∼ = 1/2 system. The dc susceptibility data are interpreted satisfactorily within the framework of a crystal-field theory and a mean-field approximation taking account of long-range dipolar interactions and anisotropic exchange interactions between the nearest-neighbor Dy3+-ions. AC susceptibility exhibits anomaly at a temperature Tice ≈ 3.13 K at frequency of f = 111 Hz, which is a signature of dynamical freezing of spins into a disordered state in compliance with the spin-ice rules. Heat capacity at zero field also shows a peak at 1.36 K and a low kink at 3.25 K which smears out on application of the magnetic field. The calculated magnetic entropy of DGS at zero field is 2.82 J K−1(mol-Dy)−1, which is much less than the Pauling spin-ice value of 4.1 J K−1mol−1. The spin-ice entropy is restored with a value of 4.50 J K−1(mol-Dy)−1 at a field of 1 T. The zero-point entropy of DGS becomes 2.94 J K−1(mol-Dy)−1 which is larger than Pauling zero-point entropy of 1.686 J K−1mol−1 for cannonical dipolar spin-ice materials, e.g., Dy2Ti2O7 and Ho2Ti2O7. The enhanced entropy of DGS may be induced due to random chemical disorder and varied chemical pressure of B-site (GaSb tetrahedra) ions. Thus, the present study creates a new pathway to extend the horizon of spin-ice physics.

Phenanthroimidazole substituted imidazo[1,2-a]pyridine derivatives for deep-blue electroluminescence with CIEy ∼ 0.08

Blue emitting materials with balanced charge carrying capacity are crucial for effective OLED. Phenanthroimidazole based deep blue materials are developed with a donor–acceptor configuration to optimize charge balance in OLEDs. In this work, three new dipolar materials based on the phenanthroimidazole-imidazopyridine conjugated system were synthesized and characterized. The position and number of phenanthroimidazole substituents are changed to study structure property relationships. All derivatives carried superb thermal stability and high photoluminescence quantum yield. Dyesin which phenanthroimidazole chromophore linked at thepara-position of C2 phenyl ring showed the red-shifted emission band. The positive solvatochromism was observed with the increase of solvent polarity, associated with the intramolecular charge transfer at excited state. The electrochemical measurement revealed that the fluorophores have low-lying LUMO energy levels. Further, doped devices were fabricated with these emitters to estimate the EL performances. Among all the emitters, the doped device fabricated with a dye containing phenanthroimidazole chromophore at para-position of C2 phenyl showed superior electroluminescence performance with CIE coordinates (0.16, 0.08).

A reciprocal relation with application in the study of the dislocations

In our article, we deduce a reciprocal relation in the context of dipolar porous materials. As an application, we analyze the effect of the dipolar structure on bodies charges which are similar to a dislocation of seismic type. Our results appear as generalizations of equivalent statements from the simpler theory of classical elastic bodies and they cover the more complicated theory of thermoelastic bodies with a dipolar structure.

Dipolar HCP materials as alternatives to DMF solvent for azide-based synthesis

Hypercrosslinked polymers HCP-DMF and HCP-DMF-SO3H containing abundant and flexible DMF moieties were designed and synthesized.

Conformational transitions and helical structures of a dipolar chain in external electric fields.

The conformational behavior of a single dipolar chain in a uniform electric field is investigated by molecular dynamics simulations. The dipolar chain is modeled as a backbone bead-on-spring chain of equally charged beads, each connected by a rigid spring with an oppositely charged side bead that can freely rotate around the backbone bead. In the strong coupling regime, when the dipolar chain is in the globular state due to a strong electrostatic correlational attraction, the application of an electric field causes the chain swelling and elongation along the field direction. In the weak coupling regime, a qualitatively new regime is found when the swollen dipolar chain shrinks along the field direction adopting flattened conformations due to the field-induced anisotropy of the chain rigidity and the head-to-tail attraction of the dipoles orienting along the field lines. A novel helical conformation is detected for low-polar media and strong electric fields. An increasing rigidity of the backbone chain leads to some stabilization of the helical conformation and the formation of double and triple helices as well as flat spread springs. Fine tuning of the interplay between dipolar and volume interactions by external electric fields induces re-orientation of rod-like dipolar chains in dilute solutions. The obtained results can provide new ways to control dipolar polymer conformations and design materials with responsive properties.

On-Surface Chemistry Induced by Long-Lived Excitons: (NO)2 Dissociation on C60.

Solid-state excitonic excitations play an increasingly important role in optoelectronic and light harvesting processes due to their ubiquitous presence in dipolar two-dimensional materials. Here we show that long-lived solid-state excitons induce chemical reactions in adsorbed molecules and thus convert light into chemical energy. For the model system (NO)2 dimer adsorbed on ordered c(4×4) C60 films, time-of-flight measurements following UV laser excitation reveal a slow and a fast dissociative desorption channel, which are assigned to intersystem crossing and internal conversion, respectively, by time-dependent density functional theory calculations.

Johari-Goldstein relaxation in glass electrets

We investigate the dielectric response in the glass-electret state of two dipolar glass-forming materials. This unusual polar glassy state of matter is produced when a dipolar liquid is supercooled under the influence of a high electric dc field, which leads to partial orientational order of the molecules carrying a dipole moment. Investigation of the prepared glass-electrets by using low-field dielectric spectroscopy reveals a clear modification of their dielectric response in the regime of the Johari-Goldstein beta-relaxation, pointing to a small but significant increase of its relaxation strength compared to the normal glass. We discuss the implications of this finding for the still controversial microscopic interpretation of the Johari-Goldstein relaxation, an inherent property of glassy matter.

A study on the thermoelasticity of three-phase-lag dipolar materials with voids

With a wide applicability in solid state mechanics, the theory of continuous dipolar materials with voids is a distinctive part of microstructure theory, a theory that emerged with the necessity of eliminating the discrepancies between the classical theory and its experimental applications. These inconsistencies are caused by the influence of the microstructure of materials on the general deformations of the bodies, such as ceramics, graphite or polymers. In the present work, we study the mixed boundary value problem with initial data for the thermoelasticity of three-phase-lag dipolar materials with voids, in order to obtain the corresponding constitutive laws, using the same method as in the classical elasticity. By going deeper into the study of these materials, we achieve a uniqueness result and a reciprocal relation, using less common methods, like the dissipative inequality regarding the result of uniqueness. Along with these aspects, we demonstrate a variational principle for anisotropic and non-homogeneous materials, derived from a well-known variational principle, but studied in the context of thermoelasticity of three-phase-lag dipolar materials with voids.

On the Partition of Energies for the Backward in Time Problem of Thermoelastic Materials with a Dipolar Structure

We first formulate the mixed backward in time problem in the context of thermoelasticity for dipolar materials. To prove the consistency of this mixed problem, our first main result is regarding the uniqueness of the solution for this problem. This is obtained based on some auxiliary results, namely, four integral identities. The second main result is regarding the temporal behavior of our thermoelastic body with a dipolar structure. This behavior is studied by means of some relations on a partition of various parts of the energy associated to the solution of the problem.

Statistical features of plastic flow localization in materials

We consider the processes of plastic flow localization in dipolar materials undergoing high speed shear deformations. The mathematical model of the processes of plastic flow localization is formulated taking into account dipolar effect. We introduce the numerical algorithm which is based on adaptive mesh refinement technique. We show that this algorithm allows to increase performance of computations. We also studied the statistical properties of shear bands formation. We show that dipolar effect changes average characteristics of the processes considered such as average temperature, stress and etc. Moreover this effect leads to increase in initiation time, changes the widths of localization zones and distances between them.

Zinc(II) as a Versatile Template for Efficient Dipolar and Octupolar Second-Order Nonlinear Optical Molecular Materials §

This short review outlines the main results obtained in the field of molecular materials based on zinc coordination compounds for second-order nonlinear optics. It presents an overview of the main classes of second-order nonlinear optical (NLO) active complexes bearing monodentate, bidentate, tridentate, or tetradentate π-delocalized ligands such as substituted stilbazoles, bipyridines, phenanthrolines, terpyridines, and Schiff bases. Macrocyclic ligands such as porphyrins and phthalocyanines are not covered. This paper shows how coordination to the Zn(II) center of π-delocalized nitrogen donor ligands produces a significant enhancement of their quadratic hyperpolarizability. Dipolar complexes are mainly presented, but octupolar zinc complexes are also presented. The coverage is mainly focused on NLO properties that are measured at the molecular level, working in solution, by means of the electric field-induced second harmonic generation (EFISH) or the hyper-Rayleigh scattering (HRS) techniques.

On the boundary value problem in the nonlinear theory of dipolar elastic materials

In our study, we formulate the boundary value problem in the context of the nonlinear theory of dipolar, porous, and elastic materials. For this problem, some existence and uniqueness results are proven. The results are natural generalizations of the results obtained by Langenbach for the classical elastic bodies.

Bimolecular Recombination of Charge Carriers in Polar Amorphous Organic Semiconductors: Effect of Spatial Correlation of the Random Energy Landscape

We present a simple model of the bimolecular charge carrier recombination in polar amorphous organic semiconductors where the dominant part of the energetic disorder is provided by permanent dipoles and show that the recombination rate constant could be much smaller than the corresponding Langevin rate constant. The reason for the strong decrease of the rate constant is the long range spatial correlation of the random energy landscape in amorphous dipolar materials, without spatial correlation even strong disorder does not modify the Langevin rate constant. Our study shows that the significant suppression of the bimolecular recombination could take place in homogeneous amorphous organic semiconductors and does not need large scale inhomogeneity of the material.

Minimum Principle for a Composite Modeled as Two Interacting Dipolar Continua

The present paper generalizes the results obtained by R. Reiss for classical elastic bodies to composites modeled as mixtures of dipolar elastic materials.

The collective behavior of shear strain localizations in dipolar materials

We study the collective behavior of shear bands in HY-100 steel and OFHC copper taking into account the dipolar effects. Starting from mathematical model, we present new numerical methodology that allows one to simulate the processes of shear strain localization in nonpolar and dipolar materials. The verification procedure was performed to prove the efficiency and accuracy of the proposed method. Using the proposed algorithm we investigate the statistical characteristics of the shear strain localization processes in dipolar materials and compare results with nonpolar case. In particular, we obtain the statistical distributions of the width of localization zones and distance between them.

The theory of generalized thermoelasticity with fractional order strain for dipolar materials with double porosity

This article continues the work on dipolar thermoelastic materials, which are a special case of multipolar continuum mechanics. This theory allows a double-porous structure: a macro-porosity related to pores in the material and a microporosity, which shows fissures in the porous skeleton. This paper constructs a mathematical model for dipolar materials, which have a double-porosity structure by considering a fractional order Duhamel–Neumann stress–strain relation. The heat conduction is described by Cattaneo’s equations. The results are the constitutive equations of the linear theory of thermoelasticity with fractional order strain. The equations are valid for anisotropic materials and are called the Duhamel–Neumann equations with fractional order. Finally, the isotropic case is considered under the conditions of plane strain in order to perform some numerical simulations for samples of porous copper.

Charge transport and exciton dissociation in organic solar cells consisting of dipolar donors mixed withC70

We investigate dipolar donor materials mixed with a ${\mathrm{C}}_{70}$ acceptor in an organic photovoltaic (OPV) cell. Dipolar donors that have donor-acceptor-acceptor (d-a-a\ensuremath{'}) structure result in high conductivity pathways due to close coupling between neighboring molecules in the mixed films. We analyze the charge transfer properties of the dipolar donor:${\mathrm{C}}_{70}$ mixtures and corresponding neat donors using a combination of time-resolved electroluminescence from intermolecular polaron pair states and conductive tip atomic force microscopy, from which we infer that dimers of the d-a-a\ensuremath{'} donors tend to form a continuous network of nanocrystalline clusters within the blends. Additional insights are provided by quantum-mechanical calculations of hole transfer coupling and hopping rates between donor molecules using nearest-neighbor donor packing motifs taken from crystal structural data. The approximation using only nearest-neighbor interactions leads to good agreement between donor hole hopping rates and the conductive properties of the donor:${\mathrm{C}}_{70}$ blends. This represents a significant simplification from requiring details of the nano- and mesoscale morphologies of thin films to estimate their electronic characteristics. Using these dipolar donors, we obtain a maximum power conversion efficiency of $9.6\ifmmode\pm\else\textpm\fi{}0.5%$ under 1 sun, AM1.5G simulated illumination for an OPV comprised of an active layer containing a dipolar donor mixed with ${\mathrm{C}}_{70}$.

Strongly Dipolar Polythiourea and Polyurea Dielectrics with High Electrical Breakdown, Low Loss, and High Electrical Energy Density

Dielectric materials with high electric energy density and low loss are of great importance for applications in modern electronics and electrical systems. Strongly dipolar materials have the potential to reach relatively higher dielectric constants than the widely used non-polar or weakly dipolar polymers, as well as a much lower loss than that of nonlinear high K polymer dielectrics or polymer–ceramic composites. To realize the high energy density while maintaining the low dielectric loss, aromatic polythioureas and polyureas with high dipole moments, high dipole densities, tunable molecular structures and dielectric properties were investigated. High energy density (>24 J/cm3), high breakdown strength (>800 MV/m), and high charge–discharge efficiency (>90%) can be achieved in the new polymers. The molecular structure and film surface morphology were also studied; it is of great importance to optimize the fabrication process to make high-quality thin films.

Colloidal ribbons and rings from Janus magnetic rods

Dipolar particles are fundamental building blocks in nature and technology, yet the effect of particle anisotropy is seldom explored. Here, we fabricate colloidal silica rods coated with a hemicylindrical magnetic layer to satisfy multiple criteria: nearly monodisperse, easily imaged and magnetic interaction that dominates over gravity. We confirm long-predicted features of dipolar assembly and stress the microstructural variety brought about by shape and constituent anisotropy, especially by extrapolating knowledge learned from literal molecules. In this colloidal system, we describe analogies to liquid crystalline deformations with bend, splay and twist; an analogy to cis/trans isomerism in organic molecules, which in our system can be controllably and reversibly switched; and a field-switching methodology to direct single ribbons into not only single but also multiple rings that can subsequently undergo hierarchical self-assembly. We highlight subtle material issues of control and design rules for reconfigurable dipolar materials with building blocks of complex shape.