Charge Transport Channels Research Articles

Sequentially Processed Bulk-Heterojunction-Buried Structure for Efficient Organic Solar Cells with 500nm Thickness.

Large-area printing fabrication is a distinctive feature of organic solar cells (OSCs). However, the advance of upscalable fabrication is challenged by the thickness of organic active layers considering the importance of both exciton dissociation and charge collection. In this work, a bulk-heterojunction-buried (buried-BHJ) structure is introduced by sequential deposition to realize efficient exciton dissociation and charge collection, thereby contributing to efficient OSCs with 500nm thick active layers. The buried-BHJ distributes donor and acceptor phases in the vertical direction as charge transport channels, while numerous BHJ interfaces are buried in each phase to facilitate exciton dissociation simultaneously. It is found that buried-BHJ configurations possess efficient exciton dissociation and rapid charge transport, resulting in reduced recombination losses. In comparison with traditional structures, the buried-BHJ structure displays a decent tolerance to film thickness. In particular, a power conversion efficiency of 16.0% is achieved with active layers at a thickness of 500nm. To the best of the authors' knowledge, this represents the champion efficiency of thick film OSCs.

In-situ polymerized electrolyte from a bifunctional additive for Li+ bulk phase migration and high-flux interface transport in lithium metal batteries

As a promising candidate of next-generation high-energy storage system, lithium metal batteries (LMBs) are still hindered by safety problems mainly derived from the leakage of liquid electrolytes and growth of lithium dendrite. Hence, electrolyte design and modification of electrode interphase become a feasible strategy for future exploitation of LMBs. Critically, bulk phase migration and high-flux interface transport of Li+ present inspiration. Herein, we introduce a bifunctional initiator, antimony trifluoride (SbF3), to in-situ form poly-DOL electrolyte (PDOL, 4 mg SbF3 10DOL-1DME) and build an anode interphase containing LiF and Li3Sb alloy hybrid, of which the system has high ion conductivity (1.404 mS cm−1), required Li+ migration path and intellectualized artificial interphase film. With the guidance of fast charge transport channel and in the effort of interface functionalization, Li+ obtains fast transition channels and high-flux interfacial flow, the batteries with SbF3 display superior cycling stability. It provides an accessible method to manufacture eligible quasi-solid LMBs for improved safety application.

A-site assisted perovskite crystallization via ion-exchange MOFs for high efficient and stable perovskite solar cells

Here, a novel strategy is proposed targeting the volatility of A-site cations and the disordered arrangement of perovskite grains through employing Cs+ contained metal–organic frameworks In-aip(Cs) obtained by ion-exchange and crystalline transform. Interatomic forces between Cs-O atoms split the pore channels of the pristine In-aip, endowing In-aip(Cs) with multidimensional charge transport channels. In addition, the partially freed Cs+ in the interlayer compensates for the vacancy of A-site cations during the perovskite preparation process. The In-aip(Cs) modified perovskite films have a flat morphology, large grains and excellent optoelectronic properties. Benefiting from the high-quality perovskite films and faster charge extraction, the In-aip(Cs)-modified PSCs achieved a champion PCE of 23.03%, superior to the In-aip-modified (22.29%) and control device (21.13%). More importantly, the unencapsulated PSCs modified with In-aip(Cs) exhibited outstanding humidity and thermal stability. Over a period of almost 1000 h, the unencapsulated In-aip(Cs)-modified device retained 85% of its initial PCE after storing in a glove box at 85 °C, and retained 87% of the primary PCE upon storage in ambient condition at 25 °C under a humidity of 40%.

Coupling interface constructions of ZnO@ZnS@FeOOH for photocatalytic hydrogen production performance

Photocatalysis is a reliable method to solve energy crisis and generate green energy hydrogen. ZnO@ZnS (ZOS) formed heterojunction repressed carrier complexation and thus enhanced photocatalytic performance, but its low photoresponse efficiency limited its photocatalytic performance. Therefore, in this paper, ZnO@ZnS was modified with ethylene diamine tetraacetic acid (EDTA) to form ZnO@ZnS@FeOOH composites with coupling interface. The modification of EDTA could inhibite the oxidation of FeOOH during the synthesis process, and what’s more it could enhance the charge transfer at the heterojunction interface to promote the separation of electron-hole pairs and photoresponsive ability to further enhanced the hydrogen precipitation performance. The concentration of EDTA and Fe sources were regulated to investigate the photocatalytic hydrogen production capacity of the composites. The results indicated that the ternary composite ZnO@ZnS@FeOOH had the superior hydrogen evolution performance with the hydrogen evolution rate of 529.17 umol g−1 h−1, which was 2.4 times higher than that of ZOS. EDTA acts as an electron channel to enhance the inter-interfacial electron transfer capability, and the loading of FeOOH formed a heterojunction structure, which promoted carrier separation and enhanced the photoresponse. It’s the synergistic effect to enhanced the photocatalytic hydrogen production performance. This paper provided a method for the construction of ternary heterojunctions and interfacial charge transport channels.

Light-Triggerable and Gate-Tunable Negative Differential Resistance in Small Molecules Heterojunction.

Negative differential resistance (NDR), a phenomenon in which the current decreases when the applied voltage is increased, is attracting attention as a unique electrical property. Here, we propose a broad spectral photo/gate cotunable channel switching NDR (CS-NDR) device. The proposed CS-NDR device has superior linear gate-tunable NDR behavior and highly reproducible properties compared to the previously reported NDR devices, as the fundamental mechanism of the CS-NDR device is directly related to a charge transport channel switching by the linear increase of the applied drain voltage. We also experimentally demonstrate that the photoinduced NDR behavior of the CS-NDR device was derived from the grain boundaries of dinaphtho[2;3-b:2',3'-f]-thieno[3,2-b]thiophene. Furthermore, this work produces a 9 × 9 CS-NDR device array composed of 81 devices, providing the reproducibility and uniformity of the CS-NDR device. Finally, we successfully demonstrate the detection of text images with 81 CS-NDR devices using the proposed photo/gate cotunable NDR behavior.

High‐Reproducibility Layer‐by‐Layer Non‐Fullerene Organic Photovoltaics with 19.18% Efficiency Enabled by Vacuum‐Assisted Molecular Drift Treatment

AbstractThe thin film deposition engineering of layer‐by‐layer (LbL) non‐fullerene organic solar cells (OSCs) favors vertical phase distributions of donor:acceptor (D:A), effectively boosting the power conversion efficiency (PCE). However, previous deposition strategies mainly aimed at optimizing the morphology of LbL films, and paid limited attention to the reproducibility of device performance. To achieve high device performance and maintain reproducibility, a strategy for hierarchical morphology manipulation in LbL OSCs is developed. A series of LbL devices are fabricated by introducing vacuum‐assisted molecular drift treatment (VMDT) to the donor or acceptor layer individually or simultaneously to elucidate the functionalities of this treatment. Essentially, the VMDT provides an extended drift driving force to manipulate the donor and acceptor molecules, resulting in a well‐defined vertical phase distribution and ordered molecular packing. These enhancements facilitate improvement in the D:A interface area and charge transport channel, ultimately contributing to impressive PCEs of 19.18% from 18.27% in the LbL devices. More importantly, using VMDT overcomes the notorious batch‐dependent and heat treatment degradation issues of OSCs, leading to excellent batch‐to‐batch reproducibility and enhanced stability of the devices. This reported method provides a promising strategy available for industrial and laboratory use to controllably manipulate the morphology of LbL OSCs.

Modified Wood Fibers Spontaneously Harvest Electricity from Moisture.

With the rapid development of modern society, our demand for energy is increasing. And the extensive use of fossil energy has triggered a series of problems such as an energy crisis and environmental pollution. A moisture-enabled electric generator (MEG) is a new type of energy conversion method, which can directly convert the ubiquitous moisture in the air into electrical energy equipment. It has attracted great interest for its renewable and environmentally friendly qualities. At present, most MEGs still have low power density, strong dependence on high humidity, and high cost. Herein, we report the development of a high-efficiency MEG based on a lignocellulosic fiber frame with high-power-density, all-weather, and low-cost characteristics using a simple strategy that optimizes the charge transport channel and ion concentration difference. The MEG devices we manufactured can generate the open-circuit voltage of 0.73 V and the short-circuit current of 360 μA, and the voltage can still reach 0.6 V at less than 30% humidity. It is possible to drive commercial electronic devices such as light-emitting diodes, electronic displays, and electronic calculators by simply connecting several electric generators in series. Biomass-based moisture-enabled electric generation has a low cost, is easy to integrate on a large scale, and is green and pollution-free, providing clean energy for low-humidity or high-electricity-cost areas.

Subphthalocyanine semiconducting cocrystals with efficient super-exchange coupling

The SubPc-12H-12F cocrystal was constructed with almost identical packings of SubPc-6F(β). This study proved that the super-exchange coupling can both improve the charge carrier mobility and expand the charge transport channels in cocrystals.

Establishing rapid charge channel via synergism of oxygen vacancy and interfacial effect to promote stable photocatalytic NO purification

Developing efficient and economical photocatalysts is critical to the practical application of nitrogen oxide (NOx) photocatalytic purification technology. At the same time, the spatial separation and migration of charges were extremely limited by the energy band mismatch and limited adaptability of the heterojunction. Herein, the interfacial effect of AgBr/Bi4O5Br2 heterojunctions with oxygen vacancies (OVs) was established to modify the interface and surface properties for enhance the photocatalytic performance. As a result, the optimal OVs-Bi4O5Br2/AgBr composite exhibited a maximum NO removal rate of 66.4 % (728 ppb → 245 ppb) and high stability for 600 min under visible light. The results show that an internal electric field could be formed by the synergism of the oxygen vacancy and interfacial effect to provide a rapid charge transport channel, which improved the separation efficiency of photo-generated carriers. It also generated abundant reactive oxygen species (ROS), which enhanced the photocatalytic NO purification performance. The present work provided a valuable design strategy for rapid charge transfer-based photocatalysts for pollutant treatment.

Structural Formation and Pore Control of Freeze-Cast Directional Graphene Aerogel (DGA).

Directional graphene aerogels (DGAs) are proposed as electrode materials to alleviate ionic and mass transport issues in organic redox flow batteries (ORFBs). DGAs with high pore directionality would provide low resistance channels for effective ionic charge and liquid electrolyte transport in these devices. DGAs' porous and directional characteristics can be controlled by the growth of ice crystals during freeze casting, which is influenced by the self-diffusivity of water, phase change driving forces, water-ice graphene interactions, and convection in the water-graphene media. It is found that mass transport-related properties of DGAs, including pore size and directionality, show a significant dependence on freezing temperature, graphene oxide (GO) loadings, and synthesis vessel diameter-to-height ratio (D/H). For the freezing temperature change from -20 to -115 °C, the average pore size progressively decreased from 120 to 20 μm, and the pore directionality transitioned from lamellar to ill-defined structures. When GO loadings were increased from 2 to 10 mg/mL at a fixed freezing temperature, pore size reduction was observed with less defined directionality. Furthermore, the pore directionality diminished with an increased width-to-height aspect ratio of DGA samples due to the buoyancy-driven convective circulation, which interfered with the directional ice/pore growth. Understanding the comprehensive effects of these mechanisms enables the controlled growth of ice crystals, leading to graphene aerogels with highly directional microstructures.

Fast Interfacial Carrier Dynamics Modulated by Bidirectional Charge Transport Channels in ZnIn2 S4 -based Composite Photoanodes Probed by Scanning Photoelectrochemical Microscopy.

Limited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single-side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2 C3 Tx MXene quantum dots (MQDs) and α-Fe2 O3 nanodots (FO) are anchored on the surface of ZnIn2 S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as "electron extractor" and S-O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high-performance composite electrodes.

Fast Interfacial Carrier Dynamics Modulated by Bidirectional Charge Transport Channels in ZnIn2S4‐based Composite Photoanodes Probed by Scanning Photoelectrochemical Microscopy

AbstractLimited charge separation/transport efficiency remains the primary obstacle of achieving satisfying photoelectrochemical (PEC) water splitting performance. Therefore, it is essential to develop diverse interfacial engineering strategies to mitigate charge recombination. Despite obvious progress having been made, most works only considered a single‐side modulation in either the electrons of conduction band or the holes of valence band in a semiconductor photoanode, leading to a limited PEC performance enhancement. Beyond this conventional thinking, we developed a novel coupling modification strategy to achieve a composite electrode with bidirectional carrier transport for a better charge separation, in which Ti2C3Tx MXene quantum dots (MQDs) and α‐Fe2O3 nanodots (FO) are anchored on the surface of ZnIn2S4 (ZIS) nanoplates, resulting in markedly improved PEC water splitting of pure ZIS photoanode. Systematic studies indicated that the bidirectional charge transfer pathways were stimulated due to MQDs as “electron extractor” and S−O bonds as carriers transport channels, which synergistically favors significantly enhanced charge separation. The enhanced kinetic behavior at the FO/MQDs/ZIS interfaces was systematically and quantitatively evaluated by a series of methods, especially scanning photoelectrochemical microscopy. This work may deepen our understanding of interfacial charge separation, and provide valuable guidance for the rational design and fabrication of high‐performance composite electrodes.

Alkoxythiophene-Directed Fibrillization of Polymer Donor for Efficient Organic Solar Cells.

Realizing fibrillar molecular framework is highly encouraged in organic solar cells (OSCs) due to the merit of efficient charge carrier transport. This is however mainly achieved via the chemical structural design of photovoltaic semiconductors. In this work, through the utilization of three alkoxythiophene additives, T-2OMe, T-OEH, and T-2OEH, the intermolecular interactions among a series of BDT-type polymer donors, i.e., PM6, D18, PBDB-T, and PTB7-Th, are tuned to self-assemble into nanofibrils during solution casting. X-ray technique and molecular dynamics simulation reveal that the alkoxythiophene with (2-ethylhexyl)oxy (─OEH) chains can attach on the 2-ethylhexyl (EH) chains of these polymer donors and promote their self-assembly into 1D nanofibrils, in their neat films as well as photovoltaic blends with L8-BO. By adapting these fibrillar polymer donors to construct pseudo-bulk heterojunction (P-BHJ) OSCs via layer-by-layer deposition, generally improved device performance is seen, with power conversion efficiencies enhanced from 18.2% to 19.2% (certified 18.96%) and from 17.9% to 18.7% for the PM6/L8-BO and D18/L8-BO devices, respectively. This work provides a physical approach to promote the fibrillar charge transport channels for efficient photovoltaics.

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction.

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

Building directional charge transport channel and injecting hot electron in a ternary CeO2-based nanosheet arrays photoanode for efficient photoelectrochemical hydrogen evolution

Building directional charge transport channel and injecting hot electron in a ternary CeO2-based nanosheet arrays photoanode for efficient photoelectrochemical hydrogen evolution

In-situ free-standing inorganic 2D Cs2PbI2Cl2 nanosheets for efficient self-powered photodetectors with carbon electrode

Inorganic two-dimensional (2D) perovskites possess excellent thermal stability and high charge mobility, making them an attractive choice for stable optoelectronic devices such as photodetectors (PDs). The formation of an appropriate inorganic 2D perovskite structure is of great importance to efficient PDs, especially to that of planar self-powered photovoltaic PDs featuring perpendicular charge transport channels. Herein, we implemented morphological engineering on wide bandgap inorganic 2D perovskite, Cs2PbI2Cl2, demonstrating a successful preparation of in-situ free-standing nanosheets structure with proper charge channels for photovoltaic type self-powered PDs. Compared with its counterpart with a nanoblock morphology, the 2D nanosheet Cs2PbI2Cl2 film exhibits enhanced charge mobility and purified Ruddlesden-Popper phase that can withstand high-energy electron beam radiation, accelerated thermal aging and long-term shelf storage. Sandwiching Cs2PbI2Cl2 nanosheet film in between tin oxide (SnO2) and polythiophene (P3HT) as electron and hole acceptors, respectively, the constructed photovoltaic type structure exhibits effective dissociation of excitons at the cascade type-II interface. The nanosheets enable lower dark current and more efficient charge collection than the nanoblock structure. As a result, the self-powered photodetectors with 2D Cs2PbI2Cl2 nanosheets deliver an outstanding responsivity of 698 mW/cm2 and a detectivity of 8.6×1012 Jones. The stable PDs can be applied to monitor ultraviolet irradiation in real outdoor conditions. Our work demonstrates the significant role of morphology tuning of 2D inorganic perovskite in stable, cost-effective and efficient photodetectors.

Resonant Charge Transport Assisted by the Molecular Vibration in Single-Molecule Junction from Time-Domain ab initio Nonadiabatic Molecular Dynamics Simulations

Using ab initio nonadiabatic molecular dynamics simulation, we study the time-dependent charge transport dynamics in a single-molecule junction formed by gold (Au) electrodes and a single benzene-1,4-dithiol (BDT) molecule. Two different types of charge transport channels are found in the simulation. One is the routine non-resonant charge transfer path, which occurs in several picoseconds. The other is activated when the electronic state of the electrodes and that of the molecule get close in energy, which is referred to as the resonant charge transport. More strikingly, the resonant charge transfer occurs in an ultrafast manner within 100 fs, which notably increases the conductance of the device. Further analysis shows that the resonant charge transport is directly assisted by the B 2 and A 1 molecular vibration modes. Our study provides atomic insights into the time-dependent charge transport dynamics in single-molecule junctions, which is important for designing highly efficient single-molecule devices.

Highly permeable PA@GO loose nanofiltration membranes enabled by hierarchical transport channels for efficient dye removal

Graphene oxide (GO) membranes exhibit ultrafast water permeation properties, which have been employed in various membrane-based separations including nanofiltration for dye removal from textile wastewater. However, it’s still a great challenge to achieve precise control over the microstructure of GO membranes and obtain ultrathin GO membranes with exceptional separation efficiency and robust membrane structure. Herein, in-situ confined interfacial polymerization (IP) is proposed for fabricating loose polyamide (PA)@GO hybrid membranes with high permeance and dye rejection as well as robust membrane stability. A new diamine of sulfadiazine (SA) with intrinsic hydrophilic and conjugated sulfonamide groups is employed as cross-linker of GO membranes and monomer of PA in IP process, simultaneously. PA is in-situ synthesized in confined GO interlayer via IP process and intercalated into GO interlayer, which enlarges the interlayer spacing of GO membranes gradiently. The combination of hydrophilic PA nanofiltration layer on GO membrane surface and the PA intercalated GO membrane with varying interlayer spacing creates hierarchical transport channels for water molecules, which contributes to the high water permeance. Moreover, the less reactive SA monomer endows PA@GO selective layer with appropriate negative charge and loose transport channels, which contributes to both of high permeance and dye rejection due to Donnon effect and size exclusion effect. The PA@GO hybrid membrane exhibits high permeance of 75.5 L/(m2·h·bar) with TB dye rejection of 99.8 %, and exhibits low NaCl rejection of 11.6 %. Moreover, PA@GO hybrid membrane shows good fouling resistance and long-term stability as well as stable separation performance under harsh conditions. Both of high permeance and dye rejection of PA@GO hybrid membrane suggests that the integration of PA nanofiltration layer and GO membrane via in-situ confined interfacial polymerization can achieve the delicate control over the interlayer channel structure and the physicochemical properties of the membrane surface of GO membranes, which offers a promising method to break through the trade-off effect between permeability and selectivity of GO membranes.

ΜοS2 nanoensembles prepared by a simple solvothermal route for hydrogen evolution reaction

Electrochemical hydrogen evolution reaction (HER) is an emerging research domain aiming to supply a means of renewable energy. Transition metal dichalcogenides (TMDs) have a good potential as promising low-cost alternatives to platinum-based catalysts. Molybdenum disulfide (MoS2) nanostructures with different shapes are increasingly becoming attractive materials for HER electrocatalysis, thanks to their peculiar physical properties which depend on their composition and morphology. It is still challenging to produce MoS2 nanomaterials simply and straightforwardly. In this work, MoS2 nanoensembles and small nanoparticles were fabricated via facile solvothermal protocols. The produced structures display a competitive activity in HER, with the nanoensembles performing better than the isotropic particles. This was attributed to the abundance of their electrochemically active sites and their robust structural stability, which endowed them with remarkable endurability in electroactivity. The nanoensemble morphology ensured the creation of a well-connected array of channels for charge transport, thus favouring an ameliorated electrochemical activity.

Ionic liquid promotes the efficient photocatalytic reduction of CO2 by Cu nanodots modified oxygen-vacancy Bi2MoO6

The conversion of CO2 into useful chemical fuels through solar photocatalysis is an important means to alleviate energy and environmental problems. In this work, small-sized Cu nanodots were dispersed on the surface of bismuth molybdate containing oxygen vacancies. The Cu/ILs/OVs-BMO composite photocatalyst with high photocatalytic reduction activity was obtained. The small size of Cu nanodots can not only greatly improve the visible light absorption of the composite catalyst, but also establish an effective channel for charge transport through the close interaction between Cu nanodots and bismuth molybdate, which promotes the efficient separation of photogenerated charge carriers and increases the photocurrent by 11.04 times. The CO2 photocatalytic reduction interface reaction was improved by adding an amine-based functionalized ionic liquid. The complexation of ILs and CO2 decreased the activation energy of generating CO2 intermediate and the overpotential of the reaction. Compared with BMO, the yield of the liquid products on Cu/ILs/OVs-BMO photocatalyst increased by 17.80 times.