Dipolar Effects Research Articles

Hexafluoroisopropanol modified MXene for perovskite surface remodeling and interfacial dipole effect enhancement

The development of high-efficiency and stable perovskite (PVK) solar cells (PSCs) still faces the challenge of non-ideal interfaces between PVK and charge transport layers. Herein, the hexafluoroisopropanol (HFIP) modified two-dimensional Ti3C2Tx MXene is custom-made (MX-HFIP) and employed as the interlayer between the PVK and hole transport layer (HTL) interface by forming hydrogen bonds. The MX-HFIP serves to reinforce the interface contact and remodel the surface of PVK, leading to a high-quality PVK film with a significantly reduced defect density, suppressed nonradiative recombination, and inhibited invasion of water and oxygen. Moreover, the synergistic effect of MXene and HFIP results in an enhanced interfacial dipole effect and an optimized energy-level alignment, thereby increasing the driving force for charge extraction and transport at the PVK/HTL interface. Therefore, the MX-HFIP treated PSC achieves a substantially-enhanced power conversion efficiency (PCE) of 22.33 %, as compared to 20.05 % of the untreated device. Besides, the MX-HFIP treated PSC delivers significantly enhanced stabilities, with 88 % of its initial PCE after 1656 h of storage at 25 °C under 30 %⁓40 % relative humidity. These findings demonstrate the advancement using fluorine-rich molecule modified MXene to improve interfacial properties for enhancing performances and stabilities of optoelectronic devices.

Enhanced energy storage performance of 0.85BaTiO3–0.15Bi(Mg0.5Hf0.5)O3 films via synergistic effect of defect dipole and oxygen vacancy engineering

Dielectric capacitors are widely used in electronic devices due to their ultra-fast charge/discharge rate and ultra-high power density, but their lower energy density and poor thermal stability limit their further application. In contrast to the traditional strategy of suppressing defects, this work combines oxygen vacancies with defect dipoles to improve the breakdown strength and polarization behavior of ferroelectric films. Low concentration of oxygen vacancies and defect dipoles can trap charge carriers and increase breakdown strength, but if the concentration is too high, it can easily make films prone to breakdown. Moreover, the defect dipoles can reduce Pr by providing intrinsic restoring force for polarization switching, while excessive defect dipoles and oxygen vacancies can pin domain walls and increase Pr. By delicately controlling the concentration of oxygen vacancies and defect dipoles in the film, the BT-BMH film deposited at 0.135 mbar achieved the maximum breakdown strength and slim P-E loops, inducing the energy density to reach 108.9 J·cm-3 with an efficiency of 79.6 % at room temperature and excellent thermal stability in the wide temperature range of -100∼350 °C with the energy density of 69.1 J·cm-3. This work reveals the important significance of reasonable defect control for improving energy storage performance and provides an effective method for developing high-performance dielectric capacitors.

Quantifying the Effect of Interfacial Dipoles on the Energy Level Alignment of Metal-Halide Perovskites

Quantifying the Effect of Interfacial Dipoles on the Energy Level Alignment of Metal-Halide Perovskites

Investigating thermal conduction dynamics in ternary Carreau–Yasuda nanofluids under convective boundary conditions and exponential heat source/sink effects

The analysis of the Carreau–Yasuda nanofluid (CYNF) across a stretching surface has practical applications in several fields, such as heat exchange, engineering, and material science. Scholars may discover novel perspectives for increasing heat transfer performance, establishing advanced materials, and enhancing the efficiency of multiple engineering systems by studying the behavior of CYNF in this particular instance. The energy transfer through trihybrid CYNF flow with the effect of magnetic dipole across a stretching sheet is examined in the present study. The ternary hybrid nanofluid (THNF) has been prepared by the addition of ternary nanoparticles (NPs) in the water (50%) and ethylene glycol (50%). Titanium dioxide (TiO2), silicon dioxide (SiO2), and aluminum oxide (Al2O3) are used in base fluid. The fluid velocity and heat transfer are examined under the impact of Darcy–Forchheimer, chemical reaction, convective condition, activation energy, and exponential heat source. The fluid flow has been stated in form of velocity, energy, and concentration equations. The set of modeled equations is simplified to non-dimensional form of ordinary differential equations (ODEs) by using similarity substitutions. Numerically, the system of lowest order ODEs is calculated through the parametric continuation method. It has been noticed that the temperature field augments against the variation of viscous dissipation and heat source term. Furthermore, the magnetic dipole has significant impact to enhance the thermal curve of THNF whereas falloffs the velocity profile. It can be noticed that the energy propagation rate enhances with the rising numbers of ternary NPs, from 1.22% to 5.98% (nanofluid), 2.30% to 9.61% (hybrid nanofluid), and 3.23% to 11.12% (trihybrid nanofluid).

Enhanced magnetoelectric response in Sc-doped BiFeO3-BaTiO3 Ceramics

In recent years, the single-phase BiFeO3-BaTiO3 multiferroic ceramics have gained attention for their magnetoelectric response above room temperature, but substantial endeavors to improve the property have yielded modest results. An optimized BiFe(1-x)ScxO3-BaTiO3 composition having magnetoelectric coefficient (αME) ∼ 567 mV/(cm·Oe)) measured at the resonant frequency (∼95 kHz) is reported in this work. The high αME is attributed to the combined effect of improved piezoelectric coefficient and enhanced ferromagnetism. Improved piezoelectricity is attributed to enhanced intrinsic response caused by the octahedral distortions, and enhanced ferromagnetism is induced by the destabilized cycloidal spin structure resulting from the octahedral distortions. Besides, the addition of Sc3+ can exhibit increased resistivity and reduced defect dipole effects, which is conducive to improving electric properties.

Deciphering the Effect of Defect Dipoles on the Polarization and Electrostrain Behavior in Perovskite Ferroelectrics.

Defect dipoles are crucial for regulating electromechanical properties in piezoelectric ceramics, but their effects on polarization and electrostrain behaviors are still unclear. Here, a reasonable theoretical model is proposed and evidenced by experiments to address a long-standing puzzle of the relationship between the internal bias field and defect dipoles. By incorporating the additional polarization induced by defect dipoles, we refine the classical theory to account for the recently reported asymmetric giant-strain behaviors. Phase-field simulation reveals the electrostrain evolution in response to defect dipole elastic distortion and additional polarization. This work not only elucidates the effect of defect dipoles on polarization and electrostrain but also advances the theoretical understanding of defects in piezoelectrics.

A high-power piezoelectric ceramic with great electrical properties and temperature stability

Lead-based Pb(Zr, Ti)O3 ceramics have been widely used in high-power piezoelectric applications, but its stable operation at high temperature is still a grand challenge. In this work, the third element Pb(Mn1/3Sb2/3)O3 (PMS) was incorporated into Pb(Zr0.48Ti0.52)O3 (PZT) to design the xPb(Mn1/3Sb2/3)O3-(1-x)Pb(Zr0.48Ti0.52)O3 (PMS-PZT) ternary ceramics through the phase diagram. The ceramics with morphotropic phase boundary (MPB) structure and uniform grain size were fabricated successfully. The dielectric, ferroelectric and piezoelectric properties of the ceramics were probed respectively. Excellent piezoelectric properties (Qm=1595, kp=0.61, d33=318pC/N, tanδ=0.60 %, Tc=300℃) were obtained in 0.075PMS-0.925PZT ceramic, which can be attributed to its MPB structure and the pinning effect of defect dipoles on domain rotation. Moreover, the T-phase dominated 0.075PMS-0.925PZT ceramic obtains great temperature stability with a low variation of resonant frequency below 2.2 % and no variation of non-resonant frequency in the temperature range from 25°C to 175°C. These results make the ceramic as a good candidate for piezoelectric frequency applications that require constant performance within a wide temperature range.

Multiple enhancement effects of dipoles within polyimide cathode promoting highly efficient energy storage of lithium-ion batteries

Polyimide (PI) has been recognized as a potential organic cathode for Li-ion batteries (LIBs) due to its programmable structural design, high theoretical capacity, and resource availability. However, the poor intrinsic electrical conductivity of PI means that PI-based cathodes of LIBs have inefficient energy storage performance, especially at high current densities. In this work, the molecular structure of PI is optimized to obtain a layer-stacked crystalline PI with significantly enhanced dipoles, denoted NT-B for the first time. The dipoles in this PI are induced by the electronegative carbonyl groups from the monomer biuret and further enhanced via a π-π layer stacking effect. This work is the first to verify that the co-directional dipole enhancement effect of biuret is surprisingly different from that of monomer urea. A series of ex-situ/in-situ and theoretical DFT simulations are carried out to understand the functional mechanism of such effects. The multiple enhancement effects of the dipoles synergistically promoting the generation of a strong built-in electric field (BIEF) within NT-B are proposed based on the results obtained. It is confirmed that this BIEF plays a significant role in accelerating electron transport, which enhances the electrochemical activity of LIB cathodes. This work provides a new idea for the structural design of high-performance PI cathodes for LIBs.

Unraveling the Role of Electron‐Withdrawing Molecules for Highly Efficient and Stable Perovskite Photovoltaic

Electron‐withdrawing molecules (EWMs) have exhibited remarkable efficacy in boosting the performance of perovskite solar cells (PSCs). However, the underneath mechanisms governing their positive attributes remain inadequately understood. Herein, we conducted a comprehensive study on EWMs by comparing 2,2'‐(2,5‐cyclohexadiene‐1,4‐diylidene) bismalononitrile (TCNQ) and (2,3,5,6‐tetrafluoro‐2,5‐cyclohexadiene‐1,4‐diylidene) dimalononitrile (F4TCNQ) employed at the perovskite/hole transport layer (HTL) interfaces. Our findings reveal that EWMs simultaneously enhance chemical passivation, interface dipole effect, and chemically binding of the perovskite to the HTL. Notably, F4TCNQ, with its superior electron‐withdrawing properties, demonstrates a more pronounced impact. Consequently, PCSs modified with F4TCNQ achieved an impressive power conversion efficiency (PCE) of 25.21%, while demonstrating excellent long‐term stability. Moreover, the PCE of a larger‐area perovskite module (14.0 cm2) based on F4TCNQ reached 21.41%. This work illuminates the multifaceted mechanisms of EWMs at the interfaces in PSCs, delivering pivotal insights that pave the way for the sophisticated design and strategic application of EWMs, thereby propelling the advancement of perovskite photovoltaic technology

Unraveling the Role of Electron-Withdrawing Molecules for Highly Efficient and Stable Perovskite Photovoltaics.

Electron-withdrawing molecules (EWMs) have exhibited remarkable efficacy in boosting the performance of perovskite solar cells (PSCs). However, the underneath mechanisms governing their positive attributes remain inadequately understood. Herein, we conducted a comprehensive study on EWMs by comparing 2,2'-(2,5-cyclohexadiene-1,4-diylidene) bismalononitrile (TCNQ) and (2,3,5,6-tetrafluoro-2,5-cyclohexadiene-1,4-diylidene) dimalononitrile (F4TCNQ) employed at the perovskite/hole transport layer (HTL) interfaces. Our findings reveal that EWMs simultaneously enhance chemical passivation, interface dipole effect, and chemically binding of the perovskite to the HTL. Notably, F4TCNQ, with its superior electron-withdrawing properties, demonstrates a more pronounced impact. Consequently, PCSs modified with F4TCNQ achieved an impressive power conversion efficiency (PCE) of 25.21 %, while demonstrating excellent long-term stability. Moreover, the PCE of a larger-area perovskite module (14.0 cm2) based on F4TCNQ reached 21.41 %. This work illuminates the multifaceted mechanisms of EWMs at the interfaces in PSCs, delivering pivotal insights that pave the way for the sophisticated design and strategic application of EWMs, thereby propelling the advancement of perovskite photovoltaic technology.

Organic-Inorganic Interfacial Dipole Induced by Energy Level Alignment for Efficient Photocatalytic Sterilization.

Photocatalytic molecules are considered to be one of the most promising substitutions of antibiotics against multidrug-resistant bacterial infections. However, the strong excitonic effect greatly restricts their efficiency in antibacterial performance. Inspired by the interfacial dipole effect, a Ti3C2 MXene modified photocatalytic molecule (MTTTPyB) is designed and synthesized to enhance the yield of photogenerated carriers under light irradiation. The alignment of the energy level between Ti3C2 and MTTTPyB results in the formation of an interfacial dipole, which can provide an impetus for the separation of carriers. Under the role of a dipole electric field, these photogenerated electrons can rapidly migrate to the side of Ti3C2 for improving the separation efficiency of photogenerated electrons and holes. Thus, more electrons can be utilized to produce reactive oxygen species (ROS) under light irradiation. As a result, over 97.04% killing efficiency can be reached for Staphylococcus aureus (S. aureus) when the concentration of MTTTPyB/Ti3C2 was 50 ppm under 660 nm irradiation for 15 min. A microneedle (MN) patch made from MTTTPyB/Ti3C2 was used to treat the subcutaneous bacterial infection. This design of an organic-inorganic interface provides an effective method to minimize the excitonic effect of molecules, further expanding the platform of inorganic/organic hybrid materials for efficient phototherapy.

Quantitative Decoupling of Strong Mn─Mn Coupling on Photoluminescence of Zero‐Dimensional Hybrid Manganese Chlorides Single Crystals

AbstractStrong Mn─Mn coupling interactions, including dipolar and exchange interactions, significantly affect the photoluminescence quantum yields (PLQYs) in Mn2+‐based luminescent materials. However, clarifying the individual effects of dipole–dipole and exchange interactions on photoluminescence (PL) is challenging because these interactions may have similar effects on PL properties, and there is a lack of materials with precisely tunable Mn─Mn distances over a wide range. In this study, the influence of dipolar and exchange coupling on PLQY is quantitatively decoupled by designing a series of hybrid manganese chlorides single crystals with a wide tuning range of Mn─Mn distances, from 6.0 to 9.5 Å. It is found that the PLQY can be enhanced from 2.1% to 57.1%, and the PL lifetime increased from 0.21 to 3.81 ms as the Mn─Mn distance increased. This enhancement is solely attributed to the decreased energy transfer dominated by dipole–dipole interactions. At the shortest Mn─Mn distance of 6 Å, exchange coupling becomes dominant, resulting in an additional red‐side PL band with negligible effects on PLQY and lifetime. This work provides valuable insights into the mechanisms underlying the regulation of PLQY in Mn2⁺‐based luminescent materials.

Electromagnetic Interference Shielding Properties of SrFe12-2x(Cu0.5Co0.5Ti)xO19 Hexaferrite

Electromagnetic (EM) pollution has become one of the most severe forms of pollution for humans and electronic devices. In order to protect humans and electronic devices from electromagnetic interference (EMI), the material that could shield the EMI should be considered. Hexagonal ferrites are considered as promising candidates for EMI shielding materials. This work fabricated Cu, Co, and Ti co-doped SrFe12O19 (SrFe12–2x(Cu0.5Co0.5Ti)xO19) samples to investigate EMI shielding properties. Among the samples, the doped ones exhibited better EMI shielding performance than the undoped one, which could be judged through total shielding efficiency (SET). In addition, the samples exhibited the best shielding performance in the frequency range of 8–12 GHz (X-band), with the best value of SET = 4.20 dB for the x = 0.20 sample, which could block ~62% of the incident microwave. The x = 0.05 sample also exhibited similar values with SET = 4.17 dB. The enhancement of SET values for doped samples compared to the undoped one could be attributed to the increase in conductivity caused by doping. In addition, the enhancement of SET could also be attributed to the effects of the magnetic dipoles combined with the electric dipoles of ferrites.

Near-infrared TADF-type organic afterglow materials

Because of the energy gap law, as well as the spin-forbidden nature of triplet formation and transformation, it remains formidable task to achieve efficient and long-lived organic afterglow materials with long emission wavelengths, especially in the near-infrared region, under ambient conditions. Here we incorporate TADF-type afterglow mechanism in dopant-matrix systems which features a moderate kRISC of 101-102 s−1 to harvest triplet energies, boost afterglow efficiency and maintain afterglow lifetime. Specifically, we design a series of boron difluoride curcuminoid (CurBF2) compounds to serve as luminescent dopants. Organic matrices of crystalline nature and with carbonyl groups are selected to suppress triplet quenching by their rigid microenvironment and populate triplet states via dipole effect developed in our group. The resultant dopant-matrix systems display near-infrared TADF-type organic afterglow with emission wavelength >700 nm, quantum yield around 10 % and afterglow lifetime >10 ms, which can function as deep-penetrating and background-independent bioimaging probes.

High Open-Circuit Voltage Wide-Bandgap Perovskite Solar Cell with Interface Dipole Layer.

Wide-bandgap perovskite solar cells (PSCs) with high open-circuit voltage (Voc) represent a compelling and emerging technological advancement in high-performing perovskite-based tandem solar cells. Interfacial engineering is an effective strategy to enhance Voc in PSCs by tailoring the energy level alignments between the constituent layers. Herein, n-type quinoxaline-phosphine oxide-based small molecules with strong dipole moments is designed and introduce them as effective cathode interfacial layers. Their strong dipole effect leads to appropriate energy level alignment by tuning the work function of the Ag electrode to form an ohmic contact and enhance the built-in potential within the device, thereby improving charge-carrier transport and mitigating charge recombination. The organic interfacial layer-modified wide-bandgap PSCs exhibit a high Voc of 1.31V (deficit of <0.44V) and a power conversion efficiency (PCE) of 20.3%, significantly improved from the device without an interface dipole layer (Voc of 1.26V and PCE of 16.7%). Furthermore, the hydrophobic characteristics of the small molecules contribute to improved device stability, retaining 95% of the initial PCE after 500h in ambient air.

Local defect structure design enhanced energy storage performance in lead-free antiferroelectric ceramics

Antiferroelectrics (AFEs) are ideal candidates in dielectric, electromechanical, and electrothermal applications. NaNbO3 (NN), as a lead-free antiferroelectric (AFE) material under extensive investigation, exhibits ferroelectric (FE)-like polarization–electric field (P-E) hysteresis loops, characterized by high remnant polarization and large hysteresis. Herein, the local defect structure design is proposed to achieve high energy storage (ES) density in NN-based AFE ceramics. The pinning effect of defect dipoles and the enhancement of local structural disorder stabilize the AFE phase and reduce hysteresis losses. Consequently, an excellent ES performance of large recoverable energy density (Wrec) of 9.70 J/cm3 and high efficiency (η) of 88.75 % is concurrently obtained in NN-based relaxor AFE ceramics, with outstanding charge–discharge performance (PD∼413.2 MW/cm3, WD∼4.47 J/cm3), which are significantly improved compared to other reported values in lead-free ES ceramics. This indicates that NN-based ceramics are candidates for advanced ES capacitors and provides a feasible modulation approach for the development of new lead-free high-performance dielectric materials.

Effect of interparticle and inter-cluster dipole–dipole interactions on dynamic behavior of superparamagnetic iron oxide nanoparticles modified with citric acid

Effect of interparticle and inter-cluster dipole–dipole interactions on dynamic behavior of superparamagnetic iron oxide nanoparticles modified with citric acid

(Invited) Bioinspired Molecular Electrets: “Misbehavior” of Dipoles, Solvation, and Interfaces

Charge transfer (CT) and charge transport are of fundamental importance for sustaining life on Earth and for making our modern ways of living possible (Phys. Chem. Chem. Phys. 2020, 22, 21583-21629). Concurrently, the ubiquitous nature of electric dipoles warrants deep understanding of how they affect CT. Possessing order electric dipoles, electrets are the electrostatic analogues of magnets, and they present outstanding paradigms for exploring dipole effects on CT (Can. J. Chem. 2018, 96, 843-858). Polypeptide α-helices are some of the best-known molecular electrets. These natural structures, however, do not efficiently mediate CT at distances exceeding 2 nm, which limits their utility. Therefore, we undertake the task for developing bioinspired molecular electrets based on synthetic amino acids that provide sites for charge-hopping and allow CT beyond the 2-nm limit. Even a single electret amino-acid residue can rectify CT (Angew. Chem. Int. Ed. 2018, 57, 12365-12369; J. Am. Chem. Soc. 2014, 136, 12966-12973). The molecular macrodipoles and the CT properties of these bioinspired molecular electrets strongly depend on their structure and conformational flexibility. Sinergy between molecular-dynamics (MD) simulations and quantum-mechanical (QM) calculations provides insights into the structural properties of these macromolecules. The structures of the molecular electrets do not fluctuate much. Nevertheless, the macrodipoles of these conjugates show picosecond fluctuations with amplitudes amounting to a factor of two or three from the average values. The structural variations of the electret oligomers cannot account for the dipole fluctuations. The analysis, however, reveals that the solvent dynamics, inducing fast-oscillating Onsager reaction fields in the solvated cavities, is principally responsible for the huge dipole fluctuations. The impact of this discovery extends way beyond the realm of electrets and our explorations show that solvent-induced picosecond dipole fluctuations are a norm, rather than an exception, for solvated species and interfaces. Averaging these dipole fluctuations over 10-ps or 20-ps intervals drastically decreases their amplitudes. It indicates that they would have a minimum effect on nanosecond and sub-nanosecond CT. Nevertheless, these dipole fluctuations may have decisive effects on picosecond and sub-picosecond processes, such as ultrafast CT. These revelations about the dipole dynamics present unexplored paradigms for condensed-phase interfaces and electronic materials.

Quantifying Induced Dipole Effects in Small Molecule Permeation in a Model Phospholipid Bilayer.

The cell membrane functions as a semipermeable barrier that governs the transport of materials into and out of cells. The bilayer features a distinct dielectric gradient due to the amphiphilic nature of its lipid components. This gradient influences various aspects of small molecule permeation and the folding and functioning of membrane proteins. Here, we employ polarizable molecular dynamics simulations to elucidate the impact of the electronic environment on the permeation process. We simulated eight distinct amino-acid side chain analogs within a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer using the Drude polarizable force field (FF). Our approach includes both unbiased and umbrella sampling simulations. By using a polarizable FF, we sought to investigate explicit dipole responses in relation to local electric fields along the membrane normal. We evaluate molecular dipole moments, which exhibit variation based on their localization within the membrane, and compare the outcomes with analogous simulations using the nonpolarizable CHARMM36 FF. This comparative analysis aims to discern characteristic differences in the free energy surfaces of permeation for the various amino-acid analogs. Our results provide the first systematic quantification of the impact of employing an explicitly polarizable FF in this context compared to the fixed-charge convention inherent to nonpolarizable FFs, which may not fully capture the influence of the membrane dielectric gradient.

Nb/Mn co‐doping enhances the pyroelectric properties of Na0.5Bi4.5Ti4O15 ceramics for infrared detection

AbstractThe pyroelectric effect has wide applications in various fields, such as infrared imaging, detection, alarms, and the expanding field of smart homes. The rapid advancement of smart systems, focusing on miniaturization and integration, requires pyroelectric infrared detectors with high pyroelectric coefficients and Curie temperatures to meet the requirements of integrated processes. However, the Curie temperature of commercial lead zirconate titanate is limited to &lt;230°C, urgently looking for a breakthrough. Here, we explore pyroelectricity in Na0.5Bi4.5Ti4O15 (NBT) ceramics, characterized by a high Curie temperature (∼660°C). We systematically examined the crystal structure modifications and defect dipole effects of the Nb/Mn‐co‐doped NBT. The lattice expansion, distortion of the TiO6 octahedra, and structural transformation tendency from the orthorhombic to tetragonal phase facilitate dipole movements with increasing temperature. Furthermore, the Mn and Nb elements result in the formation of MnTi“–VO·· and NbTi·–MnTi” –NbTi· defect dipoles, inducing additional polarization changes in response to temperature variations. Finally, a significantly improved pyroelectric coefficient of 110 µC m2 K–1 and remarkable temperature stability from 25°C to 300°C is achieved in NBTM‐5Nb ceramics. This co‐doping strategy for enhancing pyroelectric performance can be expanded to other systems and substantially contribute to advancing high‐performance materials for infrared detection.