Charge Balance Research Articles

Benzotriazole‐Based 3D Four‐Arm Small Molecules Enable 19.1 % Efficiency for PM6 : Y6‐Based Ternary Organic Solar Cells

AbstractA third component featuring a planar backbone structure similar to the binary host molecule has been the preferred ingredient for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3D‐structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal‐modified (rhodanine, thiazolidinedione, and dicyano‐substituted rhodanine) benzotriazole (BTA) units, affording three four‐arm molecules, SF‐BTA1, SF‐BTA2, and SF‐BTA3, respectively. After adding these three materials to the classical system PM6 : Y6, the resulting ternary devices obtained ultra‐high power‐conversion efficiencies (PCEs) of 19.1 %, 18.7 %, and 18.8 %, respectively, compared with the binary OSCs (PCE=17.4 %). SF‐BTA1‐3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF‐BTA1‐3 also acts to enhance charge generation. Introducing SF‐BTA1‐3 could form acceptor alloys to modify the molecular energy level and inhibit the self‐aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi‐arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi‐arm materials could make OSCs more stable and efficient.

Tunable photoluminescence of intrinsic oxygen vacancies and Bi3+/Eu3+/Li+ tridoped BaZnOS for application in wLEDs

Quaternary wide-band-gap oxychalcogenides (MZnOS, M = Ca, Sr, and Ba) are underexplored inorganic semiconductors compared with pure chalcogenides or oxides, in which more dopants could be simultaneously coordinated by oxide and chalcogenide anions. In this kind of materials, color-tunable photoluminescence (PL) could well be obtained without destructing structure. Due to the need of complex conditions for synthesis compared with Ca(Sr)ZnOS, the unique structure of BaZnOS remains largely unexplored as host for application in lighting/display fields. Spectroscopic measuring combined with XPS and DFT computational studies on pristine BaZnOS reveal that the weak multi-colored self-PL were originated from the intrinsic trap states of oxygen vacancies (VO2+, VO+ and VO0). The crystallographic occupancies of dopants Bi3+/Eu3+ and Li + at Ba2+ and Zn2+ sites, respectively were proved based on the Rietveld refinements and crystal chemistry rules. Tunable and thermally stable PL in the regions of cyan, white and even yellow could be systematically obtained from the BaZnOS: Bi/Eu via changing concentrations of dopants with the help of energy transfer (ET) from the host to dopants as well as Bi to Eu. The effect of unlit Li+ is acting both as charge balancer and fluxing agent for reducing calcination temperature and improving PL efficiency. Finally, as a proof-of-concept experiment, the BaZnOS: Bi/Eu/Li phosphor converted white light emitting diode (pc-wLED) was fabricated and produced attractive performances including high CRI of 82.5, low CCT of 4024 K, CIE coordinates of (0.3462, 0.3531), and luminous efficiency (LE) of 16.5 lm/W. Altogether, the stable Bi/Eu/Li tridoped BaZnOS phosphor is a promising candidate to be applied in lighting/display fields.

Photophysical Properties of Silver Clusters in Faujasite Zeolites: Does the Crystal Size Matter?

Electrostatic interactions between the zeolite cavity and confined noble-metal nanoparticles govern the photophysical properties of these materials. A better understanding of these interactions can afford new perspectives in optoelectronics applications. We investigated this interplay by revealing the peculiar photophysical properties of Ag clusters embedded in nanosized faujasite zeolite structures. Crystal size and steady state optical properties were characterized via integrated light and electron microscopy (ILEM) and steady state spectroscopy. Extensive time-resolved spectroscopy experiments performed on femtosecond to millisecond time scales revealed excited state dynamics that are intriguingly different from those observed for their micrometer sized counterpart. Multiscale modeling investigations were performed to rationalize the effect of the crystal size on the photophysical properties. Our results indicate that for the nanosized crystals, the emissive properties as well as the radiative and nonradiative processes involving the Ag clusters are dramatically dependent on the surface charge density and surface charge balance.

Prolonging blue TADF-OLED lifetime through ytterbium doping of electron transport layer

Balanced charge carrier transport and broad carrier recombination zone are essential features for reducing triplet exciton concentration and suppressing triplet-mediated annihilation processes, which affect the performance and stability of blue-emitting organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) phenomenon. Doping of organic layers is among the most effective methods to control these features. Herein, the impact of ytterbium (Yb) doping of electron transport layer on the TADF-OLED performance, and particularly the lifetime, was thoroughly assessed. It was found that the lower doping concentrations of Yb (<10wt%) cause electron trapping and reduced current density, whereas higher Yb concentrations facilitate electron transport in the device. Although the introduction of Yb somewhat deteriorated device efficiency, it extended operational lifetime of blue-emitting device by 2 orders of magnitude (up to 46 hours at 1000 cd/m2). This was shown to occur as a result of Yb-assisted non-radiative triplet exciton quenching at the electron transport and emission layer interface, thus diminishing detrimental exciton annihilation processes.

EE-ONIOM-CT Method to Efficiently Account for the Missing Interactions in ONIOM: Energies and Analytic Gradients.

Hybrid methods such as ONIOM (QM:QM) are widely used for the study of local processes in large systems. However, the intrinsic need for system partitioning often leads to a less-than-desirable performance for some important chemical processes. This is due to the missing interactions in the chemically important model region (i.e., active site) of the high-level theory. The missing interactions can be categorized into two classes, viz. charge transfer (i.e., charge redistribution) and long-range electrostatic interactions. Our group presented two entirely different methods to treat these deficiencies individually. ONIOM-CT and ONIOM-EE methods have been demonstrated to improve the performance of ONIOM by incorporating charge transfer and missing electrostatic interactions, respectively. In general, the inclusion of the missing interactions separately in two different calculations may not be sufficient to reach a high accuracy. Thus, it is highly desirable to develop a method to correct both deficiencies simultaneously. In this work, we aim to connect the methods ONIOM-CT and ONIOM-EE for a more comprehensive treatment. A "stepwise" model was found to be necessary for a robust performance. This model employs a stepwise procedure by first satisfying the ONIOM-CT condition for charge balance before accounting for the electrostatic interactions from the rest of the system perturbatively. This has the advantage of easy interpretation due to the clear separation of the two effects. We demonstrate the performance of our method using embedding charges determined from a Mulliken population analysis. An efficient analytic gradient expression for this method is derived and implemented by requiring three sets of z-vector self-consistent equations. The performance of our method is assessed against full system calculations in high-level theory for a set of three proton transfer reactions representing different degrees of electrostatic embedding.

Model predictive and SoC balancing control of a CHB inverter in battery energy storage application using reward functions

SummaryThis article presents an improved model predictive current control algorithm combined with a novel state of charge (SoC) balancing approach for a three‐phase cascaded H‐bridge inverter in battery energy storage applications. Based on the model predictive control with elimination of redundant voltage vectors, neighboring vectors of the last voltage vectors are used to find the optimal ones in only one control cycle, which solves the problems of high computational burden and slow dynamic response. To overcome the unsuitability of the conventional cost function in SoC balancing, the reward functions that effectively balance the inter‐phase SoCs, inner‐phase SoCs, and inner‐phase dc voltages are presented respectively. Simulation and hardware‐in‐the‐loop‐based experimental results validate the effectiveness of the proposed strategy.

Fabrication of pH-responsive poly(vinyl alcohol)-based microfibers crosslinked with copolymers containing benzoxaborole and carboxy groups

Water-insoluble pH-responsive poly (vinyl alcohol) (PVA)-based microfibers were prepared using terpolymer of poly ([2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC)-co-methacrylic acid (MAAc)-co-5-methacrylamido-1,2-benzoxaborole (MAAmBO)) (TP) containing a quaternary ammonium cation, as well as carboxy and benzoxaborole groups. The surface of the microfibers could be positively charged by the permanent positive charge of the METAC units owing to the presence of the quaternary ammonium cation. The MAAc units formed a covalent bond with the hydroxy group of the vinyl alcohol unit by thermal treatment at 135 °C for 24 h, and the MAAmBO units formed a dynamic covalent bond with the diol group in PVA. After thermal crosslinking for 24 h, the PVA/TP microfibers exhibited almost 100% of the residual weight after immersion in water at 80 °C for 30 min. The diameters of the dried PVA/TP_25 wt% fibers were 21.4 ± 3.9 μm, and the swelling ratio was 1.65 ± 0.16 after immersing in water for 24 h. All microfibers showed a low degree of hemolysis (<5%). The PVA/TP_25 wt% fibers were strongly dyed with anionic acid red 1 (AR1) molecules at pH 3 and with cationic methylene blue (MB) molecules at pH 12, since the balance of the surface charge depend on the solution pH. These microfibers could be bundled and twisted to improve their mechanical properties; the required fracture energy after twisting was 2.30 ± 0.91 times higher than that before twisting.

Efficient photoelectrochemical water splitting and photocatalytic performance for graphene-bridged MoS2–Fe2O3 nanocomposite under visible light active: Insights into photocatalysis mechanism

In this work, we aim to design a new nanocomposite with an improved photocatalytic performance by the synergistic formation of a Z-scheme photocatalytic system with graphene-bridged molybdenum disulfide (MoS2) and iron oxide (Fe2O3). We fabricated graphene-bridged MoS2–Fe2O3 nanocomposites by a simple hydrothermal method for enhanced photoelectrochemical (PEC) performance and higher degradation of TC. This nanocomposite can increase carrier separation efficiency. Moreover, the photocatalysts exhibit excellent oxidation and reduction rates capabilities assessed by photocatalytic and photoelectrochemical experiments under visible light illumination. The photocatalyst showed 97% removal capability of tetracycline and photocurrent density is five times higher than of bare Fe2O3. The active specie of .O2− and ⋅OH radicals was detected by the ESR instruments during photocatalytic activity improvement that could confirm the constructed Z-scheme MoS2–Fe2O3-Graphene nanocomposite showed that two folds photocatalytic degradation greater than those of pristine MoS2 and Fe2O3. According to the results shows UV–Visible spectroscopy, photoluminescence spectroscopy, Electron impendence spectroscopy, and photocurrent response, the photo-response electrons of transfer from the conduction band of Fe2O3 could fast transport in the valence band of MoS2. The graphene bridge served as a charge-migrate channel between two materials, and the electrons in protonated MoS2 and Fe2O3 achieved a charge balance. This work provides a new strategy for further design of high-efficiency of MFG nanocomposite with graphene as the electronic mediator for environmental remediation.

Research on safe charging strategy of lithium-ion battery based on three-electrode equivalent circuit model

Under extreme conditions of low temperature or fast charging, the side reaction of lithium (Li) plating can occur on the anode surface of lithium-ion batteries (LIBs), which may cause causing capacity fade. Alarmingly, in severe cases, dendrites will grow and pierce the separator. As a result, thermal runaway will be induced, which seriously affects the safety performance of LIBs. Along these lines, to avoid Li plating during the charging process, the safe charging strategy was thoroughly investigated in this work based on the implementation of the three-electrode equivalent circuit model (ECM). More specifically, for the three-electrode LIB implanted with a reference electrode (RE), its ECM was improved based on the traditional ECM. The cathode and anode of the LIB were decoupled through the RE, whereas combined with the heat generation, transfer, and aging characteristics, a first-order RC electro-thermal coupled model of three-electrode was established, and the semi-empirical aging model of the LIB was combined to analyse the coupling characteristics between the parameters of each model. According to the acquired experimental data, the key parameters of modelling were identified and the accuracy of the model was verified. In addition, aiming at the contradiction between the fast charging and aging speed, and combined with the NSGA-II optimization algorithm, the self-adaptive multi-stage constant current constant voltage (SMCCCV) charging strategy was also proposed to avoid Li plating on the anode surface. An optimization model was thus established with the charging time and aging loss as the objective functions, resulting in three charging strategies, namely minimum charging time, minimum aging, and balanced charging. From the simulated outcomes, it was demonstrated that the anode potential was strictly maintained above the safety threshold for these three strategies. On top of that, the balanced charging strategy reduced the aging loss by 11.5 %, while the relatively equivalent charging speed compared with the traditional constant current constant voltage (CCCV) strategy was maintained. The proposed safe charging strategy based on multi-objective optimization provides some valuable insights for next-generation fast charging techniques.

Attack-resilient distributed adaptive secondary control for heterogeneous battery energy storage systems in islanded AC microgrids

For battery energy storage systems (BESSs) in islanded AC microgrids, distributed control strategy provides an effective and flexible means to implement frequency restoration, proportional active power sharing and state of charge (SoC) balancing. Nevertheless, the distributed control system is susceptible to potential cyber attacks that break the synchronization and stability. To mitigate those effects, this paper presents an attack-resilient distributed adaptive secondary control for heterogeneous BESSs in islanded AC microgrids. The proposed control method can guarantee the consensuses on BESSs’ frequency, active power and SoC simultaneously in the presence of actuator attacks, which only uses the local and neighbor’s information. Specifically, the resilience is improved significantly by introducing the dynamic control gains with adaptive updating laws. Furthermore, the stability analysis is applied to assure the robustness. Lastly, the effectiveness of the above discussed conclusions is validated and compared by case studies on an islanded AC microgrid testing system.

Nitridochromate(IV): LiSr2[CrN3

The quaternary nitridochromate(IV) LiSr2[CrN3] crystallizes in a new structure type with the non-centrosymmetric space group P21 (no. 4) with a = 5.5685(7) Å, b = 5.3828(8) Å, c = 7.5381(1) Å, and β = 92.291(8)°. Predominant structural features of the compound are slightly nonplanar trigonal units [CrN3]5-, which are connected by three-fold coordinated lithium to form slabs in the (001) plane. Shorter Cr-N bond lengths in comparison with reported nitridochromates(III), as well as diamagnetic behavior and vibrational spectroscopy data indicate Cr(IV), which is in a good agreement with the charge balance. According to electronic structure calculations, the compound is a semiconductor with a band gap of 1.19 eV.

Novel Spiro Core‐Based Hole Transport Materials for Stable Deep‐Blue OLEDs with LT95 Over 420 h

AbstractFlexible, lightweight, and cost‐effective organic light‐emitting diodes (OLEDs) show great promise for use in displays and lighting applications. However, creating highly efficient and stable deep‐blue OLEDs remains a challenge due to a lack of efficient functional materials, specifically hole transport materials (HTM). In this report, two new spiro‐HTMs are introduced with fluorene (FBP‐SFX) or dibenzofuran (DBF‐SFX) peripheral substituents. This study finds that the DBF‐SFX variant produces highly efficient deep‐blue OLEDs with a narrow emission (full‐width at half‐maximum FWHM of 25 nm) and the highest external quantum efficiency (EQE) of 33.2% among the FBP‐SFX (12.2%) and NPB (11.9%) variants. The superior performance of DBF‐SFX is attributed to its deeper highest occupied molecular orbital level (HOMO) and small trap density, which results in reduced band‐edge offset, lower turn‐on voltages, and balanced charge carrier densities. Importantly, the blue fluorescence OLED with DBF‐SFX displays exceptional device stability with LT95 over 420 h with an initial luminance of 1000 cd m−2. This is due to the stronger bond dissociation energy (BDE) and suppressed Exciton–Polaron Annihilation (EPA) using the dibenzofuran substituent. This work demonstrates a new HTM design approach using a spiro‐core architecture and dibenzofuran substituents to create efficient and long‐lasting deep‐blue OLEDs.

Comparative Analysis and Evaluation of the Different Active Cell Balancing Topologies in Lithium Ions Batteries

Series connected batteries must have their cells balanced whenever charging and discharging to extend battery lifespans, assure safe operation, and increase battery pack useful capacity. It also causes charge imbalance issues, which will result in battery cell damage and battery life loss. Several charge/discharge equalization circuits have been suggested however, presently there has been no work regarding the comparison and evaluation of the speed and efficiencies in both modes. In this study, cell balancing on dc-to-dc buck-boost converter and interleaved flyback converter topologies operating in discontinuous current mode are analyzed, designed, and implemented. A simulation model of the converter-based topologies of an active cell balancing system is proposed and designed along with a power loss analysis, efficiencies, and control technique. With the purpose of establishing an energy storage application, the system’s cells are grouped into 8 series cells for SOC balancing and 2 series cells for voltage balancing circuit design. Power loss analysis is performed to analyze the efficiency of these two converter topologies to identify which system performs better. In SOC balancing in charging mode, the buck-boost and interleaved flyback converters’ power efficiencies are 85.596% and 65.1521% respectively and during voltage balancing 93.9078% and 73.1506% respectively.

Loss Modulated Deadbeat Control for Grid Connected Inverter System

Deadbeat controllers are commonly employed in grid connected inverter systems for their fast transient response. In this paper, a loss modulated deadbeat current control (DCC) is proposed for a grid connected inverter system. This control calculates the required modulation signal by considering the losses in the system at every switching cycle. The proposed method tracks the reference current with negligible error. The loss component used in the control method eliminates the effect of sensing and computational time delay and adapts to variation in system parameter. The proposed DCC is extended for deadbeat based direct power control (DDPC) without employing inner current control loop. Further, a modified DDPC is presented to eliminate the delay of one switching cycle which is inherently present for the grid current in DCC. The proposed control concepts are realized on a multi-source fed switched capacitor based multilevel inverter. The topology considered features more number of voltage levels with less component count, high gain, self capacitor charge balancing and increased source utilization. The steady-state and transient behaviour of the control methods are verified in simulation and experimental studies for a power rating of 500 W under various system conditions. The proposed algorithms are able to track the reference signals with fast transient response and negligible steady-state error.

Plasma ionization balance in chemical-picture and average-atom models.

We propose an approximate method to calculate ion partition functions in the context of the chemical-picture representation of plasmas as an interacting mixture of various ions and free electrons under the local-thermodynamic-equilibrium conditions. The method uses the superconfiguration approach and implies that the first-order corrections to the energies of excited electron configurations due to the electron-electron interaction may be replaced by a similar first-order correction to the energy of the basic configuration of an ion with the same number of bound electrons. The method enables one to significantly speed up the calculations and generally provides quite accurate results. Using the method proposed, plasma ionization balance and average ion charges calculated on the base of the chemical-picture representation show a good agreement with the relevant average-atom data. For the case of weak electron-ion nonideality, we provide approximate relations between the chemical-picture and average-atom values of the average ion charge, chemical potential, and plasma-density depression of ionization potential.

An SOC-Based Bidirectional Virtual DC Machine Control for Energy Storage Systems in Offshore Isolated Island DC Microgrids

In order to achieve the state of charge (SOC) balance of distributed energy storage systems (ESSs) in offshore isolated island DC microgrids and enhance the inertia and damping characteristics of DC microgrids, an SOC-based bidirectional virtual DC machine (VDCM) control is presented. The control proposed has the following three improvements. Firstly, the improved VDCM control removes the power loop and torque loop on the basis of ensuring inertia and damping characteristics. Secondly, the inertia time constant and damping constant, which are related to the bus voltage difference and the change rate of bus voltage difference, are introduced to improve bus voltage dynamic performance. The proposed method overcomes the shortcoming in that traditional VDCM control cannot adaptively suppress bus voltage oscillation according to the bus voltage fluctuation amplitude. Thirdly, an improved SOC-based VDCM virtual armature resistance (VAR) is proposed to achieve rapid SOC balance. The improved SOC-based VDCM VAR is an SOC-related function added to the initial VAR. This enables the proposed VAR to have a certain adaptive ability, which can adjust the energy absorbed or released by energy storage units according to the SOC state. Compared with other controls, the control proposed takes less time to achieve SOC balance. Finally, the effectiveness and superiority of the scheme are proven by simulation cases.

Manipulation of Charge Dynamics for Efficient and Bright Blue Perovskite Light-Emitting Diodes with Chiral Ligands.

Perovskite light-emitting diodes (PeLEDs) emerge as a promising class of optoelectronic devices for next-generation displays and lighting technology. However, the performance of blue PeLEDs lags far behind that of their green and red counterparts, including the unachieved trade-off between high efficiency and high luminance, severe efficiency roll-off, and unsatisfactory power efficiency. Here, a multi-functional chiral ligand of L-phenylalanine methyl ester hydrochloride is strategically introduced into quasi-two-dimensional perovskites, which can effectively passivate defects, modulate the phase distribution, improve photoluminescence quantum yield, guarantee high-quality film morphology, and enhance charge transport. Furthermore, ladder-like hole transport layers are established, boosting charge injection and balance. The resultant sky-blue PeLEDs (the photoluminescence peak is 493nm, and the electroluminescence peak is 497nm) exhibit an external quantum efficiency of 12.43% at 1000cd m-2 and a record power efficiency of 18.42lm W-1 , rendering that the performance is among the best blue PeLEDs. This article is protected by copyright. All rights reserved.

Enhanced Charge Balance for Efficient Electroluminescence from Cesium Copper Halides.

Cesium copper halides have the advantages of high photoluminescence quantum efficiency and good stability, making them attractive for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs). However, due to their shallow conduction band and the lack of electron transport layers compatible with it, it remains a great challenge to achieve charge balance in LED devices. This drawback manifests as the accumulation of holes at the interface between the emitting layer and electron transport layer, resulting in nonradiative recombination. Here, we demonstrate an effective approach to address this issue by suppressing hole injection, which is realized through modification of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) layer with polyethylenimine. This leads to cesium-copper-halide LEDs with a high external quantum efficiency of 5.6%, representing an advance in device architecture for efficient electroluminescence from cesium copper halides.

A luminescent anionic Cadmium(II)-MOF for the detection of nitrophenol compounds and metal ions in an aqueous solution

An anionic MOF, namely, {(CH3)2NH2)2[Cd(µ4-PPTA)]·DMF·7H2O}n (1) was synthesized with 4,4′,4″,4‴-(1,4-phenylenbis(pyridine-4,2,6-triyl))tetrabenzoic acid (H4PPTA) and characterized. X-ray results showed that 1 had a four-fold interpenetrating 3D framework with dia topology and the charged balance was provided by dimethylamine cations in the framework. Due to the high emission property and stability of 1 in water, the luminescence detections of nitroaromatic compounds and metal ions were performed with 1. 1 could detect the nitrophenol compounds and metal ions in water via luminescence quenching. The detection limits were 6.84 µM for 4-nitrophenol (NP), 1.85 µM for 2,4-dinitrophenol (DNP) and 2.76 µM for 2,4,6-trinitrophenol (TNP) and 94.4 µM for Al3+, 66 µM for Cr3+, 18.3 µM for Fe3+ and 27.6 µM for Cu2+. The detections of the nitrophenol compounds by 1 were due to hydrogen bonding interaction and resonance energy transfer. Moreover, the detections of metal ions by 1 were assigned to competitive absorption and electrostatic interactions with the anionic framework.

A Digitally-Controlled Integrated Circuit Solution for Tinnitus Treatment with Charge Balancing.

An integrated circuit specified for tinnitus treatment is described. This chip, realized using a 0.18um BCD high-voltage CMOS process, is capable of generating current stimulus with any wave shape directly into the inner-ear tissue without the need for off-chip control circuitry. Used as part of a multi-chip module that can be implanted into the inner ear, this core chip contains an 8-bit digital-to-analog converter, an amplitude control block, a novel high-voltage drive and charge balance circuit, a high-voltage level shifter, an SRAM, a ROM, and an on-chip central control unit. The chip can achieve ±0.1 mV charge-balance precision.