Dipole Unit Research Articles

Tetrahydrofuran Processable Organic Solar Cells with 19.45% Efficiency Realized by Introducing High Molecular Dipole Unit Into the Terpolymer.

Developing organic solar cells (OSCs) processable with halogen-free, non-aromatic solvents is crucial for practical applications, yet challenging due to the limited solubility of most photoactive materials. This study introduces high-performance terpolymers processable in tetrahydrofuran (THF) by incorporating dithienophthalimide (DPI) into the PM6 backbone. DPI extends the absorption band, lowers HOMO levels, and improves THF solubility and film crystallinity through its large dipole moment effect. Optimal PBD-10:L8-BO devices processed with THF achieved a competitive power conversion efficiency (PCE) of 18.79%, approaching chloroform-processed devices (19.04%). By introducing PBTz-F as a second donor, ternary OSCs reached an impressive 19.45% PCE when processed with THF. This improvement stems from enhanced photon generation, improved morphology, better charge transport, longer exciton lifetimes, efficient charge dissociation and collection, and suppressed recombination. These PCEs of 18.79% and 19.45% for binary and ternary blend OSCs, respectively, represent the highest reported efficiencies for OSCs processed with halogen-free, non-aromatic solvents. This work demonstrates significant progress in eco-friendly OSC fabrication, paving the way for more sustainable and commercially viable organic photovoltaic technologies.

Tradeoff between Intermolecular Interaction and Backbone Disorder by High Molecular Dipole Block for Improving Blend Morphology of Polymer Solar Cells

AbstractConstructing terpolymer has attracted increasing attention as a strategy to improve the performance of polymer solar cell. Terpolymer usually offers an opportunity to lower the frontier molecular orbital energy level, introduces additional absorption band and sometimes optimizes the morphology of the active blend. Generally, the additional segment in terpolymer backbone inevitably introduces backbone disorder, which causes entropy rises. However, selecting a suitable dipole unit introduces extra driving forces for crystallization by enhancing intermolecular interactions. This provides a handy knob for tradeoff between intermolecular interaction and backbone disorder, thus regulating the blend morphology. Herein, a high dipole and electron‐deficient group of pyrrolo[3,4‐f]benzotriazole‐5,7(6H)‐dione (TzBI) is incorporated into the high‐performance donor polymer and a series of terpolymers with different content of TzBI are designed. As expected, the morphology is optimized gradually for improving charge generation and charge transport, also suppressing charge recombination. The champion device with 10% TzBI exhibited a power conversion efficiency (PCE) of 18.36%, which is 5% increase compared to the controlled device. This study presents a charming terpolymer strategy by highly electron‐deficient and high dipole segment to realize a tradeoff between intermolecular interaction and backbone disorder, facilitating the optimization of morphology and elevation of fill factor and device efficiency.

A Millimeter-Wave Ultrawideband Tightly Coupled Dipole Array Antenna for Vehicle Communication

This letter presents a millimeter-wave (mmWave) ultrawideband tightly coupled dipole array (TCDA) for vehicle communication. The designed array antenna has eight dipole unit cells arranged in one dimension. A special Marchand balun with comb-type perforated structure is developed to realize the unbalance-to-balance transformation and match the impedance. The proposed unit cell of the array achieves a 1:7.6 bandwidth (5.7 GHz--43.3 GHz) with active reflection coefficient less than −6 dB during the simulation. Meanwhile, the antenna achieves a low profile of 0.087 λl, where λl is the free-space wavelength at the lower cut-off frequency. Then, a prototype with scanning angle up to 45° is fabricated and measured to validate the proposed structure. The measured realized gain of the array is 8 dBi at the center frequency of 18 GHz. The measured and simulated results are in good agreement, which confirms the simulation results and validate the proposed design.

Three-dimensional accurate modeling of nematic liquid crystal based dipole unit for reconfigurable reflectarray at 100 GHz

In this paper, a three-dimensional accurate modeling of nematic liquid crystal (LC) has been presented for the analysis of reconfigurable reflectarray cells based on LC. Both single-dipole and multiple-dipoles constructed on a LC substrate are designed as the reflectarray unit cell. Considering the inhomogeneous and anisotropic effects, the orientation of the LC molecules at each point of the LC layer involved in the unit cell under the external electrostatic field is obtained by the finite difference numerical modeling method. Utilizing the accurate modeling results of LC, the reflection constants of the reflectarray unit cells have been simulated and also have been compared with that of in the conventional model which usually assumes the LC is homogeneous and isotropic (HOMI). The error of phase range of the unit cell between the two models can exceed 45° in the single-resonant unit cell, and is more than 290° in the multi-resonant unit cell, which will seriously affect the practical application. The permittivity of LC in the unit cells under different applied voltages also has been calculated and given. Moreover, the gain radiation pattern of the reflectarray consisting of the proposed LC based double-dipoles unit cell is simulated in two models. The simulation results show that, in the accurate modeling, the gain and scanning angle range of the reflectarray obtained by the HOMI model change significantly because the phase-shift of the same unit cell for the incident wave is greatly different in the two models, which indicates that the HOMI model can no longer meet the needs of the design of LC based multi-dipoles reflectarray. Therefore, the accurate modeling method needs to be considered and cannot be ignored when studying and designing LC based devices.

10.15507/2079-6900.23.202101.91–109

A hydrodynamic mechanism of movement of a micro/nanomotor with a dipole charge induced by an electro-catalytic reaction on its surface and the formation of charges in the surrounding liquid is proposed. For this, the dynamics of a dipole aggregate in a cloud of small oppositely charged particles in a viscous fluid surrounding it is simulated. Under the action of the field of the aggregate, the particles in the cloud are set in motion, which forms a flow in the surrounding fluid. In turn, the flow creates a hydrodynamic force that moves the aggregate. The hydrodynamic interaction of all particles in the cloud with each other and with the dipole aggregate is taken into account at their different distributions in the liquid around the dipole. The total charge of all small particles can be either equal to zero or have a non-zero value. The calculations carried out confirmed the possibility of the dipole unit to move in all the cases considered as a result of action of the hydrodynamic force created by the formed flow of the surrounding fluid. In this case, the speed and direction of dipole movement significantly depends both on the distribution of small particles in the surrounding liquid and on their total charge. As the result of asymmetry in the distribution of small charged particles in the surrounding fluid, dipole unit will move not only in longitudinal but also in transverse direction. This leads to the need to use some mechanism of controlling its movement. As such a mechanism the action of an external field can be used, orienting the dipole unit in a given direction of motion. It is proposed to use an external magnetic field for such control. In this case, the dipole aggregate must have a magnetic moment due to the presence of a magnetizable nucleus inside the particles.

Characteristic Mode Inspired Dual-Polarized Double-Layer Metasurface Lens

In the following, we propose a dual-polarized double-layer metasurface lens based on split dipole unit cells. The characteristic mode analysis (CMA) of a split electric dipole shows two characteristic modes over the band of interest. By exciting these two modes with a certain phase difference, the reflection at normal incidence can be canceled. Inspired by this idea, a planar dual-polarized unit cell based on four pairs of split electric dipoles is designed on a single-layer substrate. A phase range of 396° and a transmission coefficient with a magnitude higher than 0.8 are achieved. For experimental verification, a metasurface lens with 36×36 elements is designed at 30 GHz with a focal diameter ratio of 0.84. The measured peak gain is 31.6 dBi at 31 GHz with an aperture efficiency of 45% and 1 dB/3 dB gain bandwidth of 7.3%/14%, respectively. Due to the dual-polarized operation, the relative high aperture efficiency, and the low-cost design, the proposed metasurface lens is a promising candidate for millimeter-wave communication, e.g., 5G and satellite communication systems.

Compact folded dipole metasurface for high anomalous reflection angles with low harmonic levels

A dense unit cell array used in a metasurface for a high reflection angle (θr > 50°) leads to high coupling among the unit cells; thus, parasitic reflections are unavoidable. The up-do-date patch-based metasurfaces for high reflection angles were electrically large (> 80 λ2), but for a practical point of view, a more compact metasurface design is needed. As a solution for these issues, we use the folded dipole-based unit cells with closed-loop currents for low near-field coupling and design compact metasurfaces (~ 40 λ2) for high reflection angles (θr = 56° and 70°) at 10 GHz. The folded dipole unit cells are arranged according to the recently developed non-linear phase boundary condition for low harmonic reflections. As a counterpart, we also designed a metasurface using conventional patch-shaped unit cells with the same reflection phases (θr = 70°). In experiments, the folded dipole metasurface shows lower harmonic levels (θr = 0° and − 70°) and a comparable anomalous reflection (θr = 70°) versus the patch-shaped metasurface. The time-domain analysis demonstrates that the low harmonic levels from the folded dipole metasurface are due to low scattering from the guided waves and the edge scattering. The proposed compact folded dipole-based metasurface with low undesired harmonics can be used as a practical reflect-array for millimeter-wave communication links.

Direct visualization of irreducible ferrielectricity in crystals

In solids, charge polarity can one-to-one correspond to spin polarity phenomenologically, e.g., ferroelectricity/ferromagnetism, antiferroelectricity/antiferromagnetism, and even dipole-vortex/magnetic-vortex, but ferrielectricity/ferrimagnetism kept telling a disparate story in microscopic level. Since the definition of a charge dipole involves more than one ion, there may be multiple choices for a dipole unit, which makes most ferrielectric orders equivalent to ferroelectric ones, i.e., this ferrielectricity is not necessary to be a real independent branch of polarity. In this work, by using the spherical aberration-corrected scanning transmission electron microscope, we visualize a nontrivial ferrielectric structural evolution in BaFe2Se3, in which the development of two polar sub-lattices is out-of-sync, for which we term it as irreducible ferrielectricity. Such irreducible ferrielectricity leads to a non-monotonic behavior for the temperature-dependent polarization, and even a compensation point in the ordered state. Our finding unambiguously distinguishes ferrielectrics from ferroelectrics in solids.

Synergistic Effects of External Electric Field and Solvent Vapor Annealing with Different Polarities to Enhance β-Phase and Carrier Mobility of the Poly(9,9-dioctylfluorene) Films

In this work, the synergistic effects of external electric field(EEF) and solvent vapor annealing to enhance β-phase and carrier mobility of poly(9,9-dioctylfluorene)(PFO) films were investigated. It is found that EEF can promote the PFO β-phase conformation transition and orientate the PFO chains along the EEF direction with the assistance of polar solvent vapor annealing. PFO chain orderness is closely related to the solvent polarity. In particular, the β-phase content in the annealed film of strong polar chloroform vapor increases from 18.7% to 34.9% after EEF treatment. Meanwhile a characteristic needle-like crystal is formed in the film, as a result, the hole mobility is enhanced by an order of magnitude. The mechanism can be attributed to the fast polarization of solvent dipole under the action of EEF, thus forming a driving force that greatly facilitates the orientation of PFO dipole unit. Research also reveals that EEF driving of the PFO chains does not occur with an insoluble solvent vapor since the solvent molecules cannot swell the film, thus there is insufficient free volume for PFO chains to adjust their conformation. This research enriches the understanding of the relationship between solvent vapor annealing and EEF in orientation polymers, and this method is simple and controlled, and capable of integrating into large-area thin film process, which provides new insights to manufacture low-cost and highly ordered polymer films, and is of great significance to enhance carrier mobility and efficiency of photoelectric devices based on polymer condensed matter physics.

A Full-Band Digital Television Transmitting Antenna Array With Dual-Layer Bowtie Dipole Unit

A full-band digital television (DTV) transmitting antenna array with dual-layer bowtie dipole unit is proposed in this paper. The dual-layer bowtie dipole is utilized as the antenna unit to broaden the frequency bandwidth, and its key parameters are discussed. Besides, a wideband impedance matching network with stepped complex impedance transformers is designed to achieve the full-band low voltage standing wave ratio (VSWR). For verification, a prototype is designed, fabricated, and measured. The experimental results agree well with the simulations. The measurement shows a relative bandwidth of 62.4% (455 MHz - 868 MHz) under the criterion of VSWR <; 1.15. Particularly, the VSWR is less than 1.13 within the range of 470 MHz - 862 MHz, (i.e. the full band of the DTV transmitting system). And the proposed antenna maintains a stable gain larger than 11.6 dBi over the operating frequency band with the half-power beam width of $70^{\circ } \pm ~3^{\circ }$ in the horizontal plane, which meets the requirements of the full-band signal transmission in the DTV broadcasting system.

Design and fabrication of flexible FSS polarizer

A low profile flexible linear to circular polarizer made of paper substrate is proposed in this paper. The polarizer is constructed from frequency selective surface (FSS) comprising of crossed dipole unit cell elements. The polarizer converts the linearly polarized incident electromagnetic wave to circular polarized wave at 7.0 GHz. The polarizer provides the advantage of use in conformal system, which is substantiated using bending analysis. The proposed reflective polarizer provides a 3 dB axial ratio bandwidth of 13% at the center frequency of 7.0 GHz. In addition, the proposed flexible polarizer provides stable response for angular incidences up to 30°. Prototype of the flexible FSS polarizer is fabricated and its simulation results are validated with experimental measurements.

Cross-Polarization Reduction of Linear-to-Circular Polarizing Reflective Surfaces

This letter proposes an efficient design process to reduce the cross polarization of linear-to-circular reflection polarizers illuminated by practical feeds. In particular, we propose a two-step process, where first a geometrical optimization of the unit cell is applied along one plane of the reflector, followed by a progressive rotation of the unit cell in the orthogonal plane. An offset flat polarizer comprised of dipole unit cells fed by a standard gain horn has been used to illustrate the process. Significant improvements in cross-polarization discrimination are demonstrated by simulation. Two breadboards have been manufactured, and their response is compared in order to demonstrate the validity of the design process. Good agreement with measurements is observed corroborating the proposed technique.

Nonlinear Migration Dynamics of Excess Electrons along Linear Oligopeptides Controlled by an Applied Electric Field.

Migration of an excess electron along linear oligopeptides governed by the external electric field (Eex ) which is against the inner dipole electric field is theoretically investigated, including the effects of Eex on the structural and electronic properties of electron migration. Two structural properties including electron-binding ability and the dipole moment of linear oligopeptides are sensitive to the Eex values and can be largely modulated by Eex due to the competition of Eex and the inner electric field and electron transfer caused by Eex . In the case of low Eex values, two structural properties decrease slightly, while for high Eex values, the electron-binding ability continually increases strongly, with dipole moments firstly increasing significantly and then increasing more slowly at higher Eex . Additionally, linear oligopeptides of different chain lengths influence the modulation extent of Eex and the longer the chain length is, the more sensitive modulation of Eex is. In addition, electronic properties represented by electron spin densities and singly occupied molecular orbital distributions vary with Eex intensities, leading to an unusual electron migration behavior. As Eex increases, an excess electron transfers from the N-terminus to the C-terminus and jumps over a neighboring dipole unit of two termini to other units, respectively, instead of transferring by means of a one-by-one dipole unit hopping mechanism. These findings not only promote a deeper understanding of the connection between Eex and structural and electronic properties of electron transfer behavior in peptides, but also provide a new insight into the modulation of electron migration along the oligopeptides.

A focusing reflectarray and its application in microwave virus sanitizer

AbstractIn this paper, a focusing reflectarray based on the conductor‐backed strip dipole unit cell is proposed and designed for use in the microwave virus sanitizer. Unlike traditional far‐field antennas that form a planar phase front in a specified far‐field direction, the focusing reflectarray is designed to coherently add the fields radiated from the feeding antenna at a predetermined focal point, typically within its radiating near‐field region and to ensure adequate power density to inactivate the H3N2 virus sample. Furthermore, the focusing reflectarray has a simple and planar structure compared with conventional focusing antennas. Since the microwave resonant absorption frequency of the H3N2 virus is at about 8 GHz, an 8 × 8 focusing reflectarray is designed for operation at 8 GHz. A prototype antenna is then fabricated and used for H3N2 virus sanitization. It is demonstrated experimentally that the death rate of the H3N2 virus sample is up to 93%, verifying the feasibility of the microwave virus sanitizer as well as the proposed focusing reflectarray.

Water proton configurations in structures I, II, and H clathrate hydrate unit cells

Position and orientation of water protons need to be specified when the molecular simulation studies are performed for clathrate hydrates. Positions of oxygen atoms in water are experimentally determined by X-ray diffraction analysis of clathrate hydrate structures, but positions of water hydrogen atoms in the lattice are disordered. This study reports a determination of the water proton coordinates in unit cell of structure I (sI), II (sII), and H (sH) clathrate hydrates that satisfy the ice rules, have the lowest potential energy configuration for the protons, and give a net zero dipole moment. Possible proton coordinates in the unit cell were chosen by analyzing the symmetry of protons on the hexagonal or pentagonal faces in the hydrate cages and generating all possible proton distributions which satisfy the ice rules. We found that in the sI and sII unit cells, proton distributions with small net dipole moments have fairly narrow potential energy spreads of about 1 kJ∕mol. The total Coulomb potential on a test unit charge placed in the cage center for the minimum energy∕minimum dipole unit cell configurations was calculated. In the sI small cages, the Coulomb potential energy spread in each class of cage is less than 0.1 kJ∕mol, while the potential energy spread increases to values up to 6 kJ∕mol in sH and 15 kJ∕mol in the sII cages. The guest environments inside the cages can therefore be substantially different in the sII case. Cartesian coordinates for oxygen and hydrogen atoms in the sI, sII, and sH unit cells are reported for reference.

Ferroelectricity and polarity control in solid-state flip-flop supramolecular rotators

Molecular rotation has attracted much attention with respect to the development of artificial molecular motors, in an attempt to mimic the intelligent and useful functions of biological molecular motors. Random motion of molecular rotators--for example the 180 degree flip-flop motion of a rotatory unit--causes a rotation of the local structure. Here, we show that such motion is controllable using an external electric field and demonstrate how such molecular rotators can be used as polarization rotation units in ferroelectric molecules. In particular, m-fluoroanilinium forms a hydrogen-bonding assembly with dibenzo[18]crown-6, which was introduced as the counter cation of [Ni(dmit)(2)](-) anions (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate). The supramolecular rotator of m-fluoroanilinium exhibited dipole rotation by the application of an electric field, and the crystal showed a ferroelectric transition at 348 K. These findings will open up new strategies for ferroelectric molecules where a chemically designed dipole unit enables control of the nature of the ferroelectric transition temperature.

Quantum dynamics of exciton recurrence motion in dendritic molecular aggregates

The quantum master equation approach involving weak exciton–phonon coupling has been applied to the investigation of the exciton recurrence motion in molecular aggregate models with dendritic structures. Each monomer in the models is assumed to be a dipole unit (a two-state monomer) coupled with each other by the dipole–dipole interaction. Two types of the dendritic molecular aggregates, which have mutually different interactions through the branching points, are examined. A generation of one-exciton states by an electric field and its subsequent exciton dynamics with and without relaxation terms have been investigated. It is found that the configuration of each dipole unit significantly affects the coherent motions of the exciton population. We also suggest the possibility of controlling the coherent exciton motions by tuning the frequency of an external electric field.

Exciton migration dynamics in a dendritic molecular aggregate

We investigate exciton migration dynamics in two types of dendritic molecular aggregate models, i.e., Bethe lattice, with mutually distinct intermolecular interaction between adjacent linear legs at the branching points. Each monomer molecule is assumed to be a dipole unit (a two-state model) coupled with each other by the dipole–dipole interaction. The generation of one exciton in the aggregates by the incident laser field and its subsequent dynamical behavior are investigated in a numerically exact manner. The two types of models show different exciton energy structures and distribution. It is also found that relaxation effects in the exciton states are essential for exciton migration from the periphery to the core.

Measurements of polarization reversal current of a ferroelectric liquid crystalline polymer

Abstract The polarization reversal currents of a ferroelectric liquid crystalline polymer were measured. The shape of the current signal was similar to that of low molecular weight ferroelectric liquid crystals. It was found from our calculations that the shape of the current signal was independent of the polydispersity of the polymer. In ferroelectric liquid crystalline polymers, components having different molecular weights respond cooperatively with each other to the applied voltage. From the results of our simultaneous measurements of transmittance and polarization reversal current, the dipole unit and the core moiety in the side chains appear to move in a body.

Molecular linear velocity in dielectric and far-infrared spectroscopy.

In computer simulations of the molecular dynamics of liquid water from 1 bar, 293 K to 200 kbar, 1043 K, direct statistical correlation has been observed in the laboratory frame of reference between the molecular linear center of mass velocity v and (i) the dipole unit vector \ensuremath{\mu}, and (ii) its time derivative. These results imply that dielectric relaxation and far-infrared absorption spectra are incompletely understood with theories which neglect cross correlations.