Enhanced Charge Transport Research Articles

High‐Throughput Production of Cheap Mineral‐Based Heterostructures for High Power Sodium Ion Capacitors

AbstractThe high‐throughput scalable production of inexpensive and efficient electrode materials at high current densities demanded by industry is a huge challenge for large‐scale implementation of energy storage technologies. Here, inspired by theoretical calculations that a FeS2/TiO2 heterostructure with built‐in electric field (BEF) can reduce the reaction energy barrier and enhance charge transport, the scalable production of cheap FeS2/TiO2 heterostructure is fabricated by utilizing natural ilmenite as precursor, exhibiting excellent electrochemical performances for sodium‐ion capacitors (SICs) anode. Assembling it with activated carbon (AC) cathode for SICs delivers high energy density (73.7 Wh kg−1) and high power density (10 kW kg−1) as well as outstanding cycle lifespan. Impressively, the method breaks through the traditional preparation approach by using natural minerals instead of high‐purity chemical raw materials as precursors for constructing heterojunctions, and price of the mineral is nearly five orders of magnitude lower than that of commercial chemical raw materials with high‐purity, which greatly reduces raw materials cost and is available for mass production. Similarly, the method can be extended to utilize other minerals to construct heterostructures, thus achieving expanded electrochemical performance, which exhibits huge potentials in electrochemical energy storage.

Graphene oxide/gold nanoparticle/graphite fiber microelectrodes for directing electron transfer of glucose oxidase and glucose detection

A promising electrochemical sensor is investigated using graphene oxide (GO)/gold nanoparticle (AuNP)-modified graphite electrodes to enhance charge transport in electrochemical biosensors and increase the sensitivity for glucose detection. An efficient charge transfer pathway is formed by interconnected GO nanosheets and AuNP along the graphite fiber (GF) electrode (GFE). The positive GO can adsorb glucose oxidase (GOD) by electrostatic attraction. The detected response current of the sensor is linearly related to the glucose concentration within a detection limit of 1.2 μM. Furthermore, this glucose sensor has high stability, good reproducibility and excellent selectivity for various oxidizable molecules such as dopamine (DA), uric acid (UA), ascorbic acid (AA) and other molecules causing chaff interference (fructose, lactose and galactose). It is worth noting that this work shows a new method using covalent bonds and self-assembly on the surface of GF for fabricating excellent electrochemical glucose biosensors.

Improved performance and stability of perovskite solar modules by interface modulating with graphene oxide crosslinked CsPbBr3 quantum dots

A multifunctional interface modulator GO/(CsPbBr3 QD) composite decreases resistive losses of perovskite solar modules by enhanced charge transport and decreased carrier recombination, as well as inhibiting ion/molecule diffusion.

Visualizing transport in thiazole flanked isoindigo-based donor–acceptor polymer field-effect transistors

Replacing S with Se in fluorinated isoindigo (IID) copolymers enhances charge transport properties in field-effect transistors (FET). Nonlinear optical imaging from IID FETs helps visualize transport.

Effective Double Electron Transport Layer Inducing Crystallization of Active Layer for Improving the Performance of Organic Solar Cells.

Interface modification plays an important role in enhancing the photoelectric conversion efficiency and stability of organic solar cells. In this work, alkali metal lithium chloride (LiCl) was introduced between indium tin oxide and polyethyleneimine ethoxylate (PEIE) to prepare a double-layer electron transport layer. Results show that the introduction of LiCl has dual functions. The first function is that LiCl can enhance conductivity, thereby facilitating charge collection. The second function is that the double-layer electron transport layer based on LiCl can induce the crystallization of active layer, thereby enhancing charge transport. Devices with LiCl/PEIE double layer achieve a high power conversion efficiency (PCE) of 3.84%, which is 21.5% higher than that of pristine devices (the PCE of pristine devices with pure PEIE interface layer is 3.16%).

Insights into CrS2 monolayer and [formula omitted]-CrS2/[formula omitted]-HfN2 interface for low-power digital and analog nanoelectronics

CrS2 monolayers exhibit excellent mechanical, electronic, piezoelectric and thermal properties as compared to other well-known transition metal dichalcogenides. CrS2/HfN2 van der Waals heterobilayer (vdWH) forms a pn-heterojunction where CrS2 and HfN2 act as an n-type and p-type semiconductor respectively, thereby suggesting its utility in nano-electronics and photodetectors. The perpendicular electric field is effective in manipulating band alignments and band gap in CrS2/HfN2 vdWH. Weaker electric field is able to close the band gap in the vdWH relative to CrS2 ML. Therefore, the vdWH may be a promising candidate in low-power analog and digital nano-electronics. Vertical electric field is found to drive the nearly free electron gas (NFEG) states to near the Fermi level in CrS2 ML. These surface states, reported in a few low-dimensional materials, will enhance charge transport and conductivity in electronics. Furthermore, the combined effect of spin–orbit coupling and a small magnitude of vertical electric field helps to reach a type-II band alignment in the CrS2/HfN2 vdWH. It unusually shows a large spin splitting at both conduction and valence band edges, which is very crucial for ambipolar spin transport. This work demonstrates possibilities for futuristic nano-electronic devices based on CrS2 ML & CrS2 based vdWH.

Enhanced Charge Transport and Broad Absorption Enabling Record 18.13% Efficiency of PM6:Y6 Based Ternary Organic Photovoltaics with a High Fill Factor Over 80%

AbstractTernary architecture is an efficient strategy to boost desired power conversion efficiency of single‐junction organic solar cells (OSCs). Here, a ternary OSC by incorporating a compatible acceptor ITIC‐M as a third component into state‐of‐the‐art PM6:Y6 blend is reported, yielding a power conversion efficiency of 18.13% and an impressive fill factor of 80.10%. The efficiency is the highest record for the PM6:Y6 based ternary devices reported to date. The full advantages of the designed ternary heterojunction are the good complementary light absorption that increases the photocurrent, and the matched interfacial electronic structures featuring so‐called pinning energies that facilitate exciton separation and suppress charge recombination loss. Furthermore, ITIC‐M plays a vital role in optimizing the micromorphology of the ternary blend with better dispersity, well‐formed fibrillar structure and enhanced crystallinity, thus boosting the charge transport and device performance.

Intramolecular Noncovalent Interaction-Enabled Dopant-Free Hole-Transporting Materials for High-Performance Inverted Perovskite Solar Cells.

Intramolecular noncovalent interactions (INIs) have served as a powerful strategy for accessing organic semiconductors with enhanced charge transport properties. Herein, we apply the INI strategy for developing dopant-free hole-transporting materials (HTMs) by constructing two small-molecular HTMs featuring an INI-integrated backbone for high-performance perovskite solar cells (PVSCs). Upon incorporating noncovalent S⋅⋅⋅O interaction into their simple-structured backbones, the resulting HTMs, BTORA and BTORCNA, showed self-planarized backbones, tuned energy levels, enhanced thermal properties, appropriate film morphology, and effective defect passivation. More importantly, the high film crystallinity enables the materials with substantial hole mobilities, thus rendering them as promising dopant-free HTMs. Consequently, the BTORCNA-based inverted PVSCs delivered a power conversion efficiency of 21.10 % with encouraging long-term device stability, outperforming the devices based on BTRA without S⋅⋅⋅O interaction (18.40 %). This work offers a practical approach to designing charge transporting layers with high intrinsic mobilities for high-performance PVSCs.

Intramolecular Noncovalent Interaction‐Enabled Dopant‐Free Hole‐Transporting Materials for High‐Performance Inverted Perovskite Solar Cells

AbstractIntramolecular noncovalent interactions (INIs) have served as a powerful strategy for accessing organic semiconductors with enhanced charge transport properties. Herein, we apply the INI strategy for developing dopant‐free hole‐transporting materials (HTMs) by constructing two small‐molecular HTMs featuring an INI‐integrated backbone for high‐performance perovskite solar cells (PVSCs). Upon incorporating noncovalent S⋅⋅⋅O interaction into their simple‐structured backbones, the resulting HTMs, BTORA and BTORCNA, showed self‐planarized backbones, tuned energy levels, enhanced thermal properties, appropriate film morphology, and effective defect passivation. More importantly, the high film crystallinity enables the materials with substantial hole mobilities, thus rendering them as promising dopant‐free HTMs. Consequently, the BTORCNA‐based inverted PVSCs delivered a power conversion efficiency of 21.10 % with encouraging long‐term device stability, outperforming the devices based on BTRA without S⋅⋅⋅O interaction (18.40 %). This work offers a practical approach to designing charge transporting layers with high intrinsic mobilities for high‐performance PVSCs.

In Situ Epitaxial Growth of Centimeter-Sized Lead-Free (BA)2CsAgBiBr7/Cs2AgBiBr6 Heterocrystals for Self-Driven X-ray Detection.

Halide perovskite heterocrystals, composed of distinct perovskite single crystals, have generated great interest for both fundamental research and applied device designs. One of the key advantages of using such a heterocrystal is its built-in electric potential, which enhances charge transport and suppresses the noise in the solid-state devices. On the basis of this strategy, high-performance optoelectronic devices (e.g., X-ray detectors) have been successfully demonstrated. However, the toxicity of metal cations (Pb) in those reported heterocrystals hinders their wider applications. Thus, developing lead-free halide perovskite heterocrystals is significant but remains highly challenging. Here, we report a solution-processed in situ heteroepitaxial approach that enables us to create the first lead-free halide perovskite heterocrystal, (BA)2CsAgBiBr7/Cs2AgBiBr6(BA = n-butylammonium), with dimensions of up to 10 × 7 × 6 mm3. The as-grown heterocrystals have high crystalline quality and present near atomically sharp interfaces. More excitingly, the (BA)2CsAgBiBr7/Cs2AgBiBr6 heterogeneous integration allows the formation of a built-in electric potential in the junction, which triggers spontaneous charge separation/transport. Consequently, X-ray detectors using the heterocrystals can operate in a self-driven mode and exhibit an impressive sensitivity (206 μC Gy-1 cm-2) superior to that of the pristine Cs2AgBiBr6 crystal detectors, an ultralow dark current, and operational stability. Our findings provide the first demonstration of lead-free halide perovskite heterocrystals and may open up opportunities for a host of sustainable and miniaturized perovskite optoelectronic devices.

Copper hexacyanoferrate/carbon nanostructure hybrids: electrochemically switched ion-exchange electrodes for the sustainable removal of cesium from water

Herein, we report the design and fabrication of carbon supported copper hexacyanoferrate (CuHCF) based nanohybrids as potential electrode materials for electroadsorptive removal of Cs+ from aqueous solution. Specifically, we present a hydrothermal approach for the synthesis of cubic shaped CuHCF decorated carbon nanostructures (CuHCF/CNS) viz. multi-walled carbon nanotubes (CuHCF/f-CNT), graphene oxide (CuHCF/GO) and graphitic carbon nitride (CuHCF/g-C3N4). The crafted CuHCF/CNS materials exhibit an excellent ability for electroadsorptive removal of Cs+ from its aqueous solutions, due to enhanced charge transport and high surface area offered by the CNS support to the selectively ion specific CuHCF functional units in the CuHCF/CNS hybrid. Among the CuHCF/CNS hybrids crafted for the present work, the cesium uptake capacity of CuHCF/f-CNT hybrid is highest, almost 2–3-fold higher than that reported for the various state-of-art materials. The impact of electrolyte concentration, Cs+ ion concentration, and the regeneration and selectivity for Cs+ ions over K+ over the CuHCF/CNS hybrids is also presented. We opine that the results presented herein clearly reveal the fundamental requirements and the potential advantages of combining electro-adsorption and ion exchange strategy for selective and efficient removal of 137Cs+ from radioactive liquid wastes.

High‐Efficiency Sb2(S,Se)3 Solar Cells with New Hole Transport Layer‐Free Back Architecture via 2D Titanium‐Carbide Mxene

AbstractMXene, a class of 2D materials of metal carbide or nitride, has attracted a lot of attention recently due to its excellent optical and electrical properties. In this work, titanium‐carbide MXene (Ti3C2Tx) is introduced as a back electrode in Sb2(S,Se)3 thin‐film solar cells (FTO/CdS/Sb2(S,Se)3/MXene) for the first time, which displaces traditional carbon (C) and gold (Au) electrodes entirely. Impressively, thanks to its high conductivity, mild reflectivity, and flexible flake architecture, the MXene‐based device performance outperforms typical C and Au electrodes by 153% and 77%, respectively. Specifically, the tunable work function of MXene and a beneficial Sb–O bond formed between Sb2(S,Se)3 and MXene efficiently suppress the recombination and enhance charge transport by enjoying the unique merit of the rich terminal groups of MXene. As a result, the best efficiency of 8.29% of MXene‐based Sb2(S,Se)3 solar device is achieved, which represents the highest performance of noble metal and/or hole transport layer‐free derived Sb2(S,Se)3 solar cells to date. This result has revealed that MXene is a feasible material to substitute the back electrode in Sb‐based solar cells to reach high efficiency, low cost, and high stability.

Polymerized Small‐Molecule Acceptor as an Interface Modulator to Increase the Performance of All‐Small‐Molecule Solar Cells

AbstractModulating the morphology of all‐small‐molecule organic solar cells (ASM‐OSCs) has proved to be a considerable challenge in the context of efficient exciton dissociation and charge transport. Regulating the morphology of ASM‐OSCs is a great challenge due to the low viscosity of the small molecules, which tend to form large domain sizes and loose molecular packing, especially in the interfacial region. Here, a polymerized small‐molecule acceptor (PJ1) is introduced as an interface modulator to strengthen the interfacial molecular interactions in a high‐efficiency system, consisting of a novel small molecule donor (ZR‐TT) and a widely used acceptor (Y6). Optimized ASM‐OSCs exhibit a power conversion efficiency (PCE) of 14.33% without any additives. A small amount of PJ1 effectively condenses the morphology, enhances the crystallinity of the blend, and decreases the domain sizes. Upon 3% PJ1 addition in the blends, the accelerated hole transfer and the enhanced charge transport ultimately lead to an increased PCE of 15.54% with improved short circuit current and fill factor. Notably, the generality of this interfacial modulator strategy is proved by using PJ1 in three other ASM‐OSCs and using another polymerized host acceptor, PYT‐F‐o.

Hydrothermal synthesis of CuO/g-C3N4 nanosheets for visible-light driven photodegradation of methylene blue

In this article, we synthesized pure CuO, and a g-C3N4/CuO heterostructure using a hydrothermal technique. The synthesized samples were evaluated using different analytical techniques, demonstrating that the addition of g-C3N4 substantially altered the crystallinity, energy bandgap, particle size, and morphology. The interfacial contact between g-C3N4 and CuO, as well as the formation of heterostructure between them, was confirmed by XPS and TEM. We found that pure CuO, g-C3N4 and g-C3N4/CuO heterostructure has a bandgap of 1.40 eV, 2.70 eV and 1.30 eV respectively. The effectiveness of photodegradation of MB dye was observed to be 78%, 72% and 94% for pure CuO, g-C3N4 and g-C3N4/CuO after 100 min of visible light illumination. All samples exhibit pseudo-first-order kinetics for photodegradation of MB dye with good recyclability up to five cycles. The higher photodegradation efficiency of g-C3N4/CuO is may be attributed to its lower bandgap energy, enhanced charge transport, and reduced charge recombination than pure CuO and g-C3N4. Hence, designing g-C3N4/CuO heterostructure can be a potential approach towards wastewater treatment.

Enhancement of Charge Transport of a Dye-Sensitized Solar Cell Utilizing TiO2 Quantum Dot Photoelectrode Film

A dye-sensitized solar cell (DSC) is the third generation of solar technology, utilizing TiO2 nanoparticles with sizes of 20–30 nm as the photoelectrode material. The integration of smaller nanoparticles has the advantage of providing a larger surface area, yet the presence of grain boundaries is inevitable, resulting in a higher probability of electron trapping. This study reports on the improvement of charge transport through the integration of quantum dot (QD) TiO2 with a size of less than 10 nm as the dye absorption photoelectrode layer. The QD TiO2 samples were synthesized through sol–gel and reflux methods in a controlled pH solution without surfactants. The synthesized samples were analyzed using microscopic, diffraction, absorption, as well as spectroscopic analyses. A current–voltage and impedance analysis was used to evaluate the performance of a DSC integrated with synthesized TiO2 as the photoelectrode material. The sample with smaller crystallite structures led to a large surface area and exhibited a higher dye absorption capability. Interestingly, a DSC integrated with QD TiO2 showed a higher steady-state electron density and a lower electron recombination rate. The shallow distribution of the trap state led to an improvement of the electron trapping/de-trapping process between the Fermi level and the conduction band of oxide photoelectrode material, hence improving the lifetime of generated electrons and the overall performance of the DSC.

Light-activated interlayer contraction in two-dimensional perovskites for high-efficiency solar cells.

Understanding and tailoring the physical behaviour of halide perovskites under practical environments is critical for designing efficient and durable optoelectronic devices. Here, we report that continuous light illumination leads to >1% contraction in the out-of-plane direction in two-dimensional hybrid perovskites, which is reversible and strongly dependent on the specific superlattice packing. X-ray photoelectron spectroscopy measurements show that constant light illumination results in the accumulation of positive charges in the terminal iodine atoms, thereby enhancing the bonding character of inter-slab I-I interactions across the organic barrier and activating out-of-plane contraction. Correlated charge transport, structural and photovoltaic measurements confirm that the onset of the light-induced contraction is synchronized to a threefold increase in carrier mobility and conductivity, which is consistent with an increase in the electronic band dispersion predicted by first-principles calculations. Flux-dependent space-charge-limited current measurement reveals that light-induced interlayer contraction activates interlayer charge transport. The enhanced charge transport boosts the photovoltaic efficiency of two-dimensional perovskite solar cells up to 18.3% by increasing the device's fill factor and open-circuit voltage.

Micropatterned PEDOT with Enhanced Electrochromism and Electrochemical Tunable Diffraction

Micro-nanofabrication of conductive polymers (CPs) with functional structures is in great demand in organic electronic devices, micro-optics, and flex sensors. Here, we report the fabrication of micropatterned poly(3,4-ethylenedioxythiophene) (PEDOT) and its applications on flexible electrochromic devices and tunable diffractive optics. The localized electropolymerization of 3,4-ethylenedioxythiophene at the electrode/agarose gel stamping interface through an electrochemical wet stamping (E-WETS) technique is used to fabricate PEDOT with functional microstructures. PEDOT microdots, micro-rectangles, and interdigitated array microelectrodes are fabricated with submicron tolerance and ∼2 μm smallest feature size. Furthermore, the flexible PEDOT electrochromic devices consisting of the logo of Xiamen University are fabricated with a reversible switch of absorptivity. The improved optical and coloration-amperometric responses of electrochromism are demonstrated because of the enhanced charge transport rate of the micropatterned PEDOT. The electrochromism of the 2D PEDOT micropatterns is further used as a binary diffractive optical element to modulate the intensity and efficiency of diffracted 2D structural light because of the switchable absorptivity during doping and dedoping processes. When the potential is switched from 1 to -1 V to tune the absorptivity at ∼600 nm from low to high, the intensity of zero-order diffraction light spot decreases with the intensity of other order diffraction light spots increasing dramatically. The results demonstrate that E-WETS provides an alternative method for the fabrication of CPs with functional micro-nanostructures. The electrochemical tunable diffraction with high reversibility and fast response is of potential applications in micro-optics and flex sensors.

Unveiling the influence of SmFeO3-TiO2 nanocomposites as high performance photoanodes of dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) with boosted performances were obtained with a tri-layered photoanode structure containing compact, mesoporous plus light scattering TiO2 films. Furthermore, synthesis of SmFeO3 inorganic perovskite nanocrystalline material was accomplished via the sol-gel process which was then used to prepare diverse (0–2.5%) SmFeO3/TiO2 nanocomposite films as photoanodes of DSSCs. All materials including TiO2, SmFeO3 and SmFeO3/TiO2 nanocomposites were characterized using different analysis methods, i.e. SEM images, XRD, EDS, photoluminescence (PL), DRS, FT-IR, UV–Vis spectra as well as dye adsorption. Besides, influence of SmFeO3 nanostructure was unveiled on the performances of fabricated DSSCs. The bandgap values of the TiO2, SmFeO3 were 3.25, 1.75 eV but they were altered in the range of 1.75–3.10 eV for the (0.25–2.5%) SmFeO3 + TiO2 nanocomposites. The photocurrent density–voltage diagrams were attained to measure DSSCs’ performances. It was shown that the champion device contained 0.5% SmFeO3 + TiO2 composite photoelectrode which indicated PCE = 7.06%, JSC = 17.37 mA.cm−2, VOC = 0.77 V, FF = 0.53. As a result, the 0.5% SmFeO3 + TiO2 nanocomposite enhanced the PCE by 2.66 folds (∼60%) compared to that of reference solar cell composed of pure TiO2 with champion PCE = 4.40%, JSC = 12.75 mA.cm−2, VOC = 0.64 V, FF = 0.53. According to electrochemical impedance spectroscopy (EIS) data, among diverse devices, (0.5% SmFeO3 + TiO2) photoelectrode exhibited the lowest RCT2 value of 5.27 Ω.cm−2. In fact, SmFeO3 incorporation into the TiO2 photoanode highly boosted the JSC values of DSSCs compared to that of the device containing pure TiO2 which confirmed addition of SmFeO3 led to greatly enhanced charge transport within the DSSC through declining charge recombination. Therefore, SmFeO3 could be considered as an effective nanostructured perovskite material to fabricate high-performance DSSC devices.

Boosting the Optoelectronic Properties of Molybdenum Diselenide by Combining Phase Transition Engineering with Organic Cationic Dye Doping.

Two-dimensional layered transition metal dichalcogenides (TMDs) have been investigated intensively as next-generation semiconducting materials. However, conventional TMD-based devices exhibit large contact resistance at the interface between the TMD and the metal electrode because of Fermi level pinning and the Schottky barrier, which results in poor charge injection. Here, we present enhanced charge transport characteristics in molybdenum diselenide (MoSe2) by means of a sequential engineering process called PESOD-2H/1T (i.e., phase transition engineering combined with surface transfer organic cationic dye doping; 2H and 1T represent the trigonal prismatic and octahedral phases, respectively). Substantial improvements are observed in PESOD-processed MoSe2 phototransistors, specifically, an approximately 40 000-fold increase in effective carrier mobility and a 100 000-fold increase in photoresponsivity, compared with the mobility and photoresponsivity of intact MoSe2 phototransistors. Moreover, the PESOD-processed MoSe2 phototransistor on a flexible substrate maintains its optoelectronic properties under tensile stress, with a bending radius of 5 mm.

Enhanced photocatalytic activity of ZnO hexagonal tube/r-GO composite on degradation of organic aqueous pollutant and study of charge transport properties

ZnO hexagonal tube and ZnO/r-GO nanocomposites were synthesized by hydrothermal method and the nanostructures were characterized by XRD, UV-DRS, PL, FTIR, FESEM, and TEM techniques. The main violet emission peak of the synthesized nanostructures is due to the transition between interstitial zinc and hole (valence band) of ZnO. The potential of ZnO/r-GO nanocomposite was evaluated using methyl orange (MO) and rhodamine-B (RhB), and the results were compared with the activity of synthesized ZnO nanostructures. More than 95% of MO and RhB were by ZnO/r-GO nanocomposite and it was found to be higher than that of ZnO hexagonal tube. The degradation MO and RhB were found to follow first-order kinetics and it has a rate constant of 7.68 × 10−2and 7.83 × 10−2 min−1, respectively. These results are mainly due to the enhanced charge transport property. Trapping experiments show that superoxide radical anion and hydroxide radicals are chief species responsible for the degradation of MO and RhB. The chemical stability of the nanocomposite was evaluated by cycle test experiments and it reveals that the catalyst can be reused up to few cycles without considerable loss of photocatalytic activity. This work affords a simple stratagem to integrate ZnO hexagonal tubes and r-GO nanosheets to construct effective catalysts for the degradation of organic compounds.