Charge Mobility Research Articles

Electrostatic-elastic coupling in colloidal crystals

Abstract Electrostatic-elastic coupling in colloidal crystals, composed of a mobile Coulomb gas permeating a fixed background crystalline lattice of charged colloids, is studied on the continuum level in order to analyze the lattice-mediated interactions between mobile charges. The linearized, Debye-H{" u}ckel-like mean-field equations incorporating a minimal coupling between electrostatic and displacement fields imply an additional effective attractive interaction between mobile charges. For small screening lengths, the interactions between like mobile charges exhibit colloid lattice-mediated effective interaction, ranging from weak to strong attraction, while for large screening lengths the lattice mediated interaction is purely attractive. Continuum theory incorporating the standard lattice elasticity and electrostatics of mobile charges, augmented by the minimal electrostatic-elastic coupling terms, can serve as a baseline for more detailed microscopic models.

Evolution laws of charge mobility of transformer oil and pressboard material with temperature and electric field strength

Abstract Charge mobility, a pivotal parameter in the space charge analysis model for oil-pressboard insulation of converter transformer under DC electric fields, predominantly relies on theoretical or empirical data. The prevalent omission of empirical, measurement-based evaluations, combined with the neglect of temperature and electric field intensity effects, introduces uncertainties in the calculation of electric field and charge dynamics. Grounded on the principles of the electroacoustic pulse technique for space charge measurements, our investigation established a temperature-controlled platform to determine the charge-charge mobility in oil and pressboard insulation mediums. Utilizing diverse oil-pressboard insulation systems, this study identified the temporal patterns of both positive and negative charge mobilities and unravelled the mechanisms modulated by temperature and electric field intensity: 1) With increasing temperatures (from 20°C to 80°C) and intensifying electric field strengths (from 5kV/mm to 25kV/mm), the charge mobility within transformer oil and pressboard exhibits a rising trend. Notably, temperature variations exert the most significant influence, yielding amplifications up to 24.8 times. 2) The intrinsic properties of different transformer oils and oil-impregnated pressboards result in pronounced differences in their charge transport behaviours. Specifically, naphthenic-based oil demonstrates enhanced charge mobility relative to its paraffin-based counterpart. In contrast, transformer oils with higher kinematic viscosities exhibit diminished charge mobility compared to those with lower viscosities. 3) A linear relationship is observed between the oil absorption rate and electrical conductivity, aligning closely with the insulating pressboard's charge mobility. The evaluation of electric field and interface charge dynamics in oil-pressboard insulation under both DC and polarity-reversed conditions revealed that the electric field decay in naphthenic-based oil is more rapid than in paraffin-based oils. Moreover, both the magnitude and rate of interface charge accumulation in naphthenic-based oils exceed those in paraffin-based variants, further validating the accuracy of our charge mobility measurements and ensuing analysis.

Synergistic Effects of Solid and Solvent Additives on Film Morphology Enable Binary Organic Solar Cells with Efficiency of Over 19%

AbstractRegulating the film morphology features of the photoactive layer is critically important for developing high‐performance organic solar cells (OSCs). Adding solvent or solid additives is widely used to realize fine‐tuned film morphology. However, most high‐performance OSCs are processed only using single component additive, either solvent additive or solid additive. Herein, two structurally similar analogs of 1‐benzothiophene (BT) and benzo[1,2‐b:4,5‐b']dithiophene (BDT) are applied as volatilizable solid additives and are used with the well‐known solvent additive 1‐chloronaphthalene (CN), respectively. Comprehensive morphology analysis revealed that the addition of BT with better volatilization can promote the formation of stronger molecular packing and desirable phase separation, resulting in higher charge mobility and more efficient charge separation. However, the insufficient volatilization of BDT caused excessive aggregation, leading to severe recombination. Consequently, the PMZ‐10:Y6 based binary OSCs treated with the hybrid additives of CN and BT delivered a notable efficiency of 19.03%, which is one of the best values of the Y6‐based binary devices reported so far. Overall, this work highlights the importance of hybrid additive strategy and the reasonable combination of solid and solvent additives in further advancing the development of OSCs field.

Multi-Agent Deep Reinforcement Learning for Blockchain-Based Energy Trading in Decentralized Electric Vehicle Charger-Sharing Networks

With The integration of renewable energy sources into smart grids and electric vehicle (EV) charger-sharing networks is essential for achieving the goal of environmental sustainability. However, the uneven distribution of distributed energy trading among EVs, fixed charging stations (FCSs), and mobile charging stations (MCSs) introduces challenges such as inadequate supply at FCSs and prolonged latencies at MCSs. In this paper, we propose a multi-agent deep reinforcement learning (MADRL)-based auction algorithm for energy trading that effectively balances charger supply with energy demand in distributed EV charging markets, while also reducing total charging latency. Specifically, this involves a MADRL-based hierarchical auction that dynamically adapts to real-time conditions, optimizing the balance of supply and demand. During energy trading, each EV, acting as a learning agent, can refine its bidding strategy to participate in various local energy trading markets, thus enhancing both individual utility and global social welfare. Furthermore, we design a cross-chain scheme to securely record and verify transaction results of energy trading in decentralized EV charger-sharing networks to ensure integrity and transparency. Finally, experimental results show that the proposed algorithm significantly outperforms both the second-price and double auctions in increasing global social welfare and reducing total charging latency.

Transient Exciton-Charge Interconversion in Single-Crystal Hybrid Perovskites.

Ultrafast oscillatory transient absorption (TA) dynamics are observed in single crystals of hybrid organic-inorganic perovskite (CH3NH3)PbX3 with X = I, Br, Cl. High-density photoinduced charges, low binding energy of the excitons, efficient generation and high mobility of charges, and long diffusion length of both excitons and charges led to transient interconversion between excitons and charges with high efficiency, which is responsible for the oscillatory TA dynamics at re-excitation by the probe pulses. The pump pulses initiated a quasi-equilibrium scheme of coexisting excitons and charges with high densities, the probe pulse triggered a perturbation through interconversion between these two kinds of excited "particles," which was overlapped on the intrinsic exciton relaxation dynamics, producing an oscillatory modulation with time delay. This not only reveals important photoelectronic processes with determined time scales, but also supplies physics for applications of this group of materials.

Non‐Electron Withdrawing Unit Copolymerization to Enhance Photo‐Stability of Thiophene‐Based Organic Solar Cells

The impact of non‐electron withdrawing unit copolymerization on photostability of fullerene‐based organic solar cells is investigated using two donor polymers namely: benzodithiophene‐4,8‐dione (BDD) unit copolymerized with α‐quaterthiophene (4 T) unit (PBDD4T) and poly‐3‐hexyl‐thiophene (P3HT). The optical and electrochemical properties of the polymers reveal a deeper highest occupied molecular orbital (HOMO) and broader absorption in PBDD4T in comparison to P3HT owing to the BDD copolymerization. The copolymer achieves a higher power conversion efficiency (PCE) compared to the P3HT‐based device due to its higher VOC and Jsc that resulted from its deeper HOMO level and broader absorption. The photostability study reveals that PBDD4T‐based devices lost 14% of its initial PCE relative to the 48% reduction in PCE for P3HT‐based devices after 7 h of irradiation. Further investigation into the reasons behind the difference in the photostability suggests that photooxidation and recombination induced by irradiation in PBDD4T‐based devcie are suppressed by BDD‐copolymerization, maintaining better stability. In contrast, P3HT:PC71BM‐based solar absorber shows bimolecular recombination due to photoaging processes, which have negatively impacted the device stability. The reduction in stability of both devices is evident by lower photogenerated current attributed to reduced charge mobility and increased surface roughness.

A novel simulation of space charge decay dynamics after removing the voltage in epoxy resin composites

Abstract Epoxy resin serves as a critical insulating component in ultra-high voltage dry direct current bushings. However, the accumulation of space charges within the epoxy resin, a byproduct of charge mobility, poses a significant risk to the reliability and operational safety of bushings. Conventional space charge attenuation models, especially after voltage removal, have limited use in simulations aimed at understanding this phenomenon. This study introduces an improved model integrating the bipolar charge transport mechanism with space charge decay based on the hopping conduction mechanism and Schottky’s theorem, establishes a theoretical framework for predicting the space charge behavior following voltage removal, and conducts a simulation to investigate the decay process within the internal structure of epoxy resin and measure the residual charges after voltage removal using the pulsed electro-acoustic method. The experimental data validate the accuracy of the proposed model and theoretical assumptions. The findings show that the remaining negative charges after voltage removal are not enhanced by the field enhancement; the anodic positive and cathodic positive charges are distributed in two-segment discontinuous traps, whereas the negative charges are distributed in one-segment traps. The model identifies two distinct trapping sites for anodic and cathodic positive charges, and one trapping site for negative charges. After voltage removal, when the field strength exceeded 40 kV mm−1, positive charges exist near the upper and lower electrodes, and negative charges exist near the center of the specimen. The consistency between the simulated predictions and experimental data proves the effectiveness of the proposed model in accurately simulating the space charge decay in epoxy materials after voltage removal.

Isolation and characterisation of monolayer phosphorene analogues

Atomically thin group IV monochalcogenides or phosphorene analogues are a promising family of materials. Theoretical calculations predict that monolayers (MLs) should be semiconducting, ferroelectric and ferroelastic at room temperature, exhibit large charge mobilities and large non-linear optical response. Yet, experimental studies of these systems are scarce because of the difficulty to produce such MLs. Here we focus on two members of this family: GeSe and SnS. We demonstrate a simple mechanical exfoliation method to produce ML samples on gold substrates. We observe the evolution of the Raman scattering as a function of layers and the anisotropic optical response from reflectance contrast measurements. To the best of our knowledge this is the first report of mechanical exfoliation down to the ML of these materials and the first realisation of ML GeSe.

Microscopic analysis of low but stable perovskite solar cell device performance using electron spin resonance

Perovskite solar cells have attracted much attention as next-generation solar cells. However, a typical hole-transport material, spiro-OMeTAD, has associated difficulties including tedious synthesis and high cost. To overcome these shortcomings, an easily synthesized and low-cost hole-transport material has been developed: HND-2NOMe. Although HND-2NOMe has high local charge mobility because of the quasi-planar structure, its lower device performance is a weak point, the cause of which has not yet been clarified. Here, we analyse the source of the lower performance by clarifying the internal states from a microscopic viewpoint using electron spin resonance. We observe hole diffusion from perovskite to HND-2NOMe under dark conditions, indicating hole barrier formation at the perovskite/HND-2NOMe interface, leading to lower performance. Although such a barrier is formed, less hole accumulation for the HND-2NOMe-based cells under solar irradiation occurs, which is related to the stable performance. The sources of the lower but stable performance are crucially important for providing guidelines for improving the device performance.

Towards Perpetual Wireless Rechargeable Sensor Networks with Path Optimization of Mobile Chargers

Towards Perpetual Wireless Rechargeable Sensor Networks with Path Optimization of Mobile Chargers

Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells.

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

Long-Lived Charge Carrier Photogeneration in a Cooperative Supramolecular Double-Cable Polymer.

A newly designed C3-symmetric disc-shaped chromophore, BTT(NDI)3, features electron accepting naphthalene diimides linked to an electron donor BTT core. BTT(NDI)3 self-assembles in apolar solvents into highly ordered, chiral supramolecular fibers through π-π and 3-fold hydrogen-bonding interactions. This leads to a cooperative formation of plane-to-plane stacking of BTTs and J-aggregation of the outer NDIs. Such a structure ensures high charge mobility. Only photoexcitation of BTT in the BTT(NDI)3 polymers triggers a unidirectional electron transfer from BTT to NDI and results in (BTT•+-NDI•-) lifetimes that are by up to 3 orders of magnitude longer compared to (NDI•+-NDI•-) that is formed upon NDI photoexcitation. A multiphasic decay implies ambipolar pathways for charge carriers, that is, electron and hole delocalization along the respective BTT and NDI stacks. Our supramolecular approach offers potential for developing functional supramolecular polymers with continuous pathways for electrons and holes and, in turn, minimizing charge recombination losses in organic photovoltaic devices.

COIN BASED MOBILE CHARGING USING ARDUINO

COIN BASED MOBILE CHARGING USING ARDUINO

Harnessing Quantum Materials for Enhanced Energy Efficiency and Storage: A Comprehensive Study of Electronic Properties and Performance Optimization

This research explores the exciting potential of various quantum materials to enhance energy efficiency and storage capabilities, filling in a crucial gap in our understanding of their electronic properties and interactions. A major hurdle in this field is the lack of empirical data on key factors such as conductivity, charge mobility, and thermal stability—elements that are vital for optimizing the performance of these materials in energy applications. Our study aims to blend experimental data with computational simulations to create a robust framework for modelling how quantum materials behave under different conditions. This comprehensive approach helps lay a solid foundation for their practical use in energy technologies. We focus on an array of fascinating quantum materials, including topological insulators, transition metal dichalcogenides, and superconductors. To investigate these materials, we employ advanced techniques like scanning tunnelling microscopy and spectroscopy, which allow us to delve deep into their unique properties. While pursuing this research, we do encounter challenges. Variations in sample quality, environmental factors during experimentation, and the complexities of theoretical modelling can affect the consistency of our results and the interpretation of our data. Despite these obstacles, our findings suggest that certain quantum materials hold remarkable potential for enhancing energy storage and conversion systems through improved charge mobility and thermal stability. In fact, some materials have demonstrated conductivity levels that surpass those of traditional options, hinting at transformative applications in energy technologies. These insights highlight the importance of continuing our exploration of quantum materials, positioning them as promising candidates for tackling today’s energy challenges and paving the way for advancements in sustainable energy solutions.

Structurally Compact Penta(N,N-diphenylamino)corannulene as Dopant-free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells.

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor-(DPA)5, characterized by a bowl-shaped core with symmetric five diphenylamine groups. Compared to already-known HTMs, the bowl-shaped and relatively compact structure of cor-(DPA)5 facilitates intermolecular π-π interactions, promotes film formations, and enhances charge transport. Consequently, the cor-[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro-OMeTAD and cor-OMePTPA, our newly synthesized cor-(DPA)5 HTM is free from any ionic dopants. As a result, the dopant-free cor-[DPA(2)]5-based PSC demonstrates an impressive efficiency of 24.01%, and exhibits outstanding operational stability. It retains 96% after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Structurally Compact Penta(N,N‐diphenylamino)corannulene as Dopant‐free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor‐(DPA)5, characterized by a bowl‐shaped core with symmetric five diphenylamine groups. Compared to already‐known HTMs, the bowl‐shaped and relatively compact structure of cor‐(DPA)5 facilitates intermolecular π–π interactions, promotes film formations, and enhances charge transport. Consequently, the cor‐[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro‐OMeTAD and cor‐OMePTPA, our newly synthesized cor‐(DPA)5 HTM is free from any ionic dopants. As a result, the dopant‐free cor‐[DPA(2)]5‐based PSC demonstrates an impressive efficiency of 24.01%, and exhibits outstanding operational stability. It retains 96% after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Role of Near-IR Sensitive Asymmetric A-DA′D–π–A-type Non-Fullerene Acceptors for Efficient Organic Solar Cells: A Theoretical Insight

Non-fullerene acceptor (NFA) molecules attracted huge attention from the photovoltaic community for their potential use in organic solar cells (OSCs). Herein, we designed a series of NFA materials (AR1–AR9) for OSCs by altering end-capped moieties. We employed various advanced density functional theory (DFT) and time-dependent (TD-DFT) approaches to characterize this designed AR1–AR9 series. Compared to the synthetic reference molecule ([Formula: see text], designed molecules AR1–AR9 revealed a smaller bandgap (1.85 eV), and improved absorption spectra ([Formula: see text] 741 nm) in comparison to [Formula: see text] ([Formula: see text] 668 nm), indicating the better potential for the tailored molecules. Furthermore, the designed series (AR1–AR9) shows lower reorganization energy values (for holes and electrons) and lower binding energies (0.323 eV), whereas, improved charge mobilities, showing them better candidates for OSCs. Moreover, frontier molecular orbitals (FMO), open-circuit voltages ([Formula: see text] and improved charge-transfer characteristics have also been investigated. These findings revealed that all developed NFAs exhibited a wide range of exciton dissociation constants and enhanced absorption efficiency with a relatively lower LUMO energy level. Therefore, we believe that these materials will be beneficial in boosting the power conversion efficiency (PCE) of OSC devices by improving their optoelectronic and photophysical properties.

Chain rigidity controlled aggregation ability and solid-state microstructures for efficient stretchable conjugated polymer films

Stretchable conjugated polymer films with good electrical performance under mechanical deformation are highly desirable for soft electronics. However, the mechanical and electrical properties of these films, particularly in conjugated polymer:elastomer blends, are not fully understood at molecular level. This study explores the relationships among molecular structure, aggregation ability, film microstructure, and the electrical/mechanical properties of three diketopyrrolopyrrole -based conjugated polymers (P1, P2, P3) with decreasing backbone rigidity and their corresponding polymer:elastomer blends. The most flexible polymer P3 shows strong aggregation, which forms highly crystalline fibers to produce fragile neat film and produces large isolated crystallites restricting charge transport in blend film. As chain rigidity increases, the P1 and P2 polymers show weaker aggregation, and produce smaller crystallites in neat films with enhanced ductility. P1 and P2 based blend films display nanocrystallites polymer networks with dispersed elastomer domains. As a result, we achieved near-constant charge mobility before and after stretching under 50 % strain for P2-based blend films with well-controlled pathways for both charge transport and energy dissipation. This study demonstrates the critical role of backbone rigidity in regulating the properties of stretchable conjugated polymer films, paving the way for more reliable and deformable materials in soft electronics.

Heterojunction Organic Solar Cells with Efficient Charge Mobility and Separation Capabilities Studied by DFT.

The properties of the active layer materials play a decisive role in determining the power conversion efficiency of organic solar cells (OSCs). Chlorophyll and its derivatives are abundant and environmentally friendly functional organic molecular materials. Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we have calculated the absorption spectra and their excited state properties based on optimized ground state structures. It was found that bacteriochlorin exhibits superior structural properties, a smaller energy gap and hole reorganization energy, redshifted absorption spectra, and higher hole mobility compared to the donor D18. This suggests that bacteriochlorin exhibits superior donor properties. Comparative studies between o-AT-2Cl and m-AT-2Cl showed that o-AT-2Cl had superior acceptor properties, implying that differences in substitution positions can influence the physicochemical properties of non-fullerene acceptors (NFAs). Subsequently, six bulk heterojunctions (BHJs) were constructed by combining three donors with nonfused ring electron acceptors, o-AT-2Cl and m-AT-2Cl. The bacteriochlorin-based BHJs performed well among them, with BChl3/o-AT-2Cl and BChl4/o-AT-2Cl having the largest interfacial charge separation rate. The results suggested that BHJs composed of bacteriochlorin and NFAs can improve OSCs' photovoltaic performance, providing a feasible scheme for designing efficient OSCs.

2D g-C3N5 p-Doping of Donor Material for High-Efficiency Organic Solar Cells.

Molecular doping of organic semiconductor is a great strategy for significantly regulating the electronic band structure of organic semiconductor while increasing charge mobility and carrier concentration. Here, a facile strategy is presented by introducing 2D g-C3N5 as a p-dopant into PM6, improving the charge mobility and hole carrier concentration of PM6. Moreover, the electron transfer between PM6 and g-C3N5 can effectively downshift the Fermi energy level and highest occupied molecular orbital (HOMO) energy level of PM6, which leads to the increase the built-in electric field of organic solar cells (OSCs). The addition of g-C3N5 also effectively enhances the crystallization of active layer, thereby improving the stability of OSCs. As a result, a champion bulk-heterojunction (BHJ) and layer-by-layer (LbL) structure OSCs are successfully achieved featuring a high-power conversion efficiency of 18.10%/18.25%, simultaneously having excellent device stability. This work shows that introducing a low concentration dopant into organic donor is an effective method for improving the electrical performance of organic donor and the efficiency of OSCs.