Good Charge Transport Research Articles

Transition Metal Ion‐Directed Coordination Polymers with Mixed Ligands: Synthesis, Structure, and Photocatalytic Activity for Hydrogen Production and Rhodamine B Degradation

Three mixed‐ligand transition metal coordination polymers with the formula of {[CuI2CuII(tpt)2(L)]·15H2O}n (1) and {[M2(H2O)5(tpt)(L)]·6H2O}n [M = Ni for 2 and Co for 3; tpt = 2,4,6‐tris(4‐pyridyl)‐1,3,5‐triazine and L = 3,3'‐disulfonyl‐4,4'‐biphenyldicarboxylate] were hydrothermally synthesized by varying the cheap paramagnetic metal ions and used as photocatalysts for hydrogen evolution from water splitting and rhodamine B (RhB) degradation. Single‐crystal structural determinations reveal that 1 is a robust pillared‐layer framework with unusual 72‐membered {Cu6(tpt)6} macrocycle‐based layers supported by tetratopic L4– connectors. Both 2 and 3 are isostructural (4 4) sheets with octahedral NiII and CoII ions extended by ditopic L4– and tpt linkages, in which the third pyridyl group of tpt is capped by pentahydrated metal ions. Due to the narrowed bandgap and good charge transport of the mixed‐valence CuI/II centers, 1 exhibits improved dual‐functional catalytic activities than 2 and 3 with the visible‐light‐driven hydrogen evolution rate and RhB degradation efficiency up to 588 μmol·g–1·h–1 and 72 % after 180‐minute irradiation. These interesting results indicate the importance of the metal ions and the dimensionality of the coordination polymers on the activity of the non‐Pt coordination polymer photocatalytic systems.

Emerging Approaches in Enhancing the Efficiency and Stability in Non‐Fullerene Organic Solar Cells

AbstractThe past three years have witnessed rapid growth in the field of organic solar cells (OSCs) based on non‐fullerene acceptors (NFAs), with intensive efforts being devoted to material development, device engineering, and understanding of device physics. The power conversion efficiency of single‐junction OSCs has now reached high values of over 18%. The boost in efficiency results from a combination of promising features in NFA OSCs, including efficient charge generation, good charge transport, and small voltage losses. In addition to efficiency, stability, which is another critical parameter for the commercialization of NFA OSCs, has also been investigated. This review summarizes recent advances in the field, highlights approaches for enhancing the efficiency and stability of NFA OSCs, and discusses possible strategies for further advances of NFA OSCs.

Anomalous electronic and thermoelectric transport properties in cubic Rb3AuO antiperovskite

We use first-principles calculations combined with self-consistent phonon (SCP) theory, electron-phonon ($e\ensuremath{-}ph$) coupling, and the Boltzmann transport equation (BTE) to investigate the electronic and thermoelectric transport properties in the cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$ antiperovskite with strongly cubic and quartic lattice anharmonicity. The combination of SCP theory and Wannier-Fourier interpolation is used to calculate the $e\ensuremath{-}ph$ coupling due to the failure of density functional perturbation theory in solving $e\ensuremath{-}ph$ matrix elements for a strongly anharmonic crystal. Our results exhibit that a high electron mobility ${\ensuremath{\mu}}_{e}$, e.g., $\ensuremath{\sim}454\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}/\mathrm{Vs}$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ from the iterative BTE solution, and a relatively weak temperature dependence of ${\ensuremath{\mu}}_{e}\ensuremath{\propto}{T}^{\ensuremath{-}1.1}$ are obtained in the $n$-type cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$. We demonstrate that the coupling between electrons and polar optical phonons is responsible for the good charge transport, which, along with the high thermopower deriving from a light and threefold degenerate conduction-band pocket around the $X$ point, leads to a very high power factor reaching $5.5\phantom{\rule{4pt}{0ex}}\mathrm{mW}/{\mathrm{mK}}^{2}$ at $800\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Meanwhile, a low lattice thermal conductivity and an undersized Lorenz number that signifies a resulting low electron thermal conductivity are also detected. As a result, a good thermoelectric performance with a figure of merit $ZT\ensuremath{\sim}1.02$ at $300\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and an anomalously high $ZT\ensuremath{\sim}3.02$ at $800\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is captured in the $n$-type cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$. This finding breaks the long-term record of $ZT<3$ in most of the reported bulk thermoelectric materials to date, and illustrates that the cubic ${\mathrm{Rb}}_{3}\mathrm{AuO}$ is an excellent candidate for thermoelectric applications.

Morphological and Surface-State Challenges in Ge Nanoparticle Applications.

The intrinsic properties of Ge in tandem with advances in its nanostructuring have resulted in its increased attention in a variety of fields as an alternative to traditional group 12-14 and 14-16 nanoparticles (NPs). The small band gap and size-dependent development of the optical properties in tandem with their good charge transport properties make Ge NPs a suitable material for optoelectronic devices. The low toxicity of Ge, together with its IR photoluminescence (PL) that overlaps with desirable biological optical windows used for tissue imaging, allows the exploitation of these materials in the field of bioimaging and as drug carriers. In addition, the ability of germanium to both exhibit high mechanical stability in its NP form and alloy with lithium and sodium metals has led to it being a highly attractive material for next-generation lithium ion and beyond-lithium batteries. While it is attracting considerable attention in a variety of areas, research on Ge NPs is still relatively nascent. Fundamental aspects of this material, such as its Bohr radius and the origin of different observed PLs, are still under debate. Moreover, the ability to produce Ge NPs with controlled dimensions and morphology is not yet as mature as for other classes of nanomaterials. In this review, the mechanisms and origins of these properties will be introduced, which we then relate to specific applications presented in the literature.

P‐97: Applications of Metal Halide Perovskite as Passive and Active Light Emitting Materials

Metal halide perovskites are promising materials for display applications as phosphors and active layers in light‐emitting diodes. Here, we briefly review the physical properties that make them suitable in such products, namely their high absorption and emission coefficients, combined with good charge transport properties and ease of fabrication. Then, we report on the development of green perovskite emitters and the fabrication of down‐conversion films for backlight units (BLUs). Finally, we summarise our recent development in perovskites LEDs, showing how we have reached commercially‐relevant efficiencies for each color channel.

Low-voltage complementary inverters using solution-processed, high-mobility organic single-crystal transistors fabricated by polymer-blend printing

Organic field-effect transistors (OFETs) have attracted great attention as key elements in Internet-of-Thing (IoT) devices due to their advantages of low cost and mass producibility made possible by printing technology. Such devices require organic semiconductors (OSCs) that intrinsically possess high carrier mobility and air stability. In addition, the demand for low-voltage operation and low power consumption has been increasing because the potential power sources for actual devices are implementable energy harvesters that supply low power and low voltages. Based on recently developed high-performance single-crystal p-type and n-type OSCs, this work demonstrated air-stable, high-mobility OFETs with low-voltage operation by using an insulating polymer-blend printing method. By comparing two acrylic polymers poly(methyl methacrylate) and poly(adamantyl methacrylate) (PADMA), having remarkably different thermal properties, we found that PADMA showing a high glass transition temperature >200 °C was suitable for device fabrication, enhancing the flexibility of OSC materials. Also, PADMA spontaneously produced good charge-transport interfaces with the OSC single crystals, leading to high carrier mobilities of 6.6 and 2.2 cm2 V−1 s−1 in p-channel and n-channel OFETs at ≤1.5 V, respectively. The current electron mobility was the highest among low voltage-operation OFETs reported so far. These high-mobility OFETs were integrated into a complementary inverter, for which a low static power consumption of 6.6 pW was confirmed. Therefore, this study reports an advantage of polymer-blend printing for OFETs with enhanced processability and performance suitable for IoT applications.

Psoralen: A Biologically Important Coumarin with Emerging Applications.

Coumarin belongs to a class of lactones that are fundamentally comprised of a benzene ring fused to an α-pyrone ring; these lactones are known as benzopyrones. Similarly, coumarin has a conjugated electron-rich framework and good charge-transport properties. Plants produce coumarin as a chemical response to protect themselves from predation. Coumarins are used in different products, such as cosmetics, additives, perfumes, aroma enhancers in various tobaccos and some alcoholic drinks, and they play a relevant role in natural products and in organic and medicinal chemistry. In addition, as candidate drugs, many coumarin compounds have strong pharmacological activity, low toxicity, high bioavailability and better curative effects and have been used to treat various types of diseases. Various endeavors were made to create coumarin-based anticoagulant, antimicrobial, antioxidant, anticancer, antidiabetic, antineurodegenerative, analgesic and anti-inflammatory agents. A class of chemical compounds called furocoumarins has phototoxic properties and is naturally synthesized via the fusion of coumarin to a furan ring in different plant species. Psoralens belong to the furocoumarin class and occur naturally in various plants, e.g., lemons, limes, and parsnips. Angelicin is an isomer of psoralens, and most furocoumarins, e.g., xanthotoxin, bergapten, and nodekenetin, are derivatives of psoralens or angelicin. The present work demonstrated that psoralen molecules exhibit anti-tumoral activity against breast cancer and influence different intracellular signals to maintain the high survival of breast cancer cells. Psoralens perform different functions, e.g., antagonize metabolic pathways, protease enzymes, and cell cycle progression and even interfere in the crosslinking between receptors and growth factor mitogenic signaling.

Ceramic grains: Highly promising hole transport material for solid state QDSSC

Polysulphide has proven to be an efficient electrolyte for QDSSC, but at the cost of corroding the counter electrode and degrading the sensitizer due to its high redox potential. In this view for the first time, we have used oxide nanoceramics as low cost, easily processable and highly porous solid-state electrolytes for QDSSCs. High residual porosity and formation of liquid phase nanodomains across grain boundaries have added advantages for adsorption and diffusion in these hole transport layer. Yttria stabilized zirconia and ceria co doped yttria stabilized zirconia are the two solid state electrolytes designed in place of polysulphide. Dopants namely Y3+ and Ce4+ in ZrO2 induces defects, oxygen vacancies and band shifts resulting in good charge transport. The interfaces and charge transfer kinetics suggests, recombination resistance offered by these ceramics avoid the back electron transfers via the downward shift of valence band (VB) much closer to that of sensitizer and also act as barriers (or passivation layer) to effectively suppress electron recombinations, resulting in high stability and Voc of the device. Devices designed with these new HTLs show efficiencies on par with polysulphide; they are extremely stable for almost up to 60 days (in ambient conditions), while cells fabricated with polysulphide electrolyte tend to degrade the device within 5 days.

Engineering Intrinsic Flexibility in Polycrystalline Molecular Semiconductor Films by Grain Boundary Plasticization.

Mechanically flexible films of the highly crystalline core-cyanated perylenediimide (PDIF-CN2) molecular semiconductor are achieved via a novel grain boundary plasticization strategy in which a specially designed polymeric binder (PB) is used to connect crystallites at the grain boundaries. The new PB has a naphthalenediimide-dithiophene π-conjugated backbone end-functionalized with PDI units. In contrast to conventional polymer-small molecule blendswhere distinct phase separation occurs, this blend film with plasticized grain boundaries exhibits a morphology typical of homogeneous PDIF-CN2 films which is preserved upon bending at radii as small as 2 mm. Thin-film transistors fabricated with PB/PDIF-CN2 blends exhibit substantial electron mobilities even after repeated bending. This design represents a new approach to realizing flexible and textured semiconducting π-electron films with good mechanicaland charge transport properties.

Neat 3D C3N4 monolithic aerogels embedded with carbon aerogels via ring-opening polymerization with high photoreactivity

Ring-opening polymerization affords an extremely powerful driver for large-scale delocalization of π-electrons and good charge transport via incorporating aromatic repeat units and rigid molecular skeleton. Herein, we first developed a branched six functional benzoxazine monomer (BZ) through Mannich condensation reaction. The rigid chain segment structure of crosslinked polybenzoxazine (PBZ) penetrated into the π-conjugated planes of C3N4 via the room-temperature HCl-catalyzed polymerization of the monomer, leading to the formation of a range of 3D C3N4 monolithic aerogels embedded with carbon aerogel. High nitrogen self-doped carbon aerogels were flexibly embedded in situ into the C3N4 matrix during the heat curing process, leading to the redshift of the C3N4 absorption edge and the increase of electrical conductivity. The special framework of the NC/C3N4 monolithic aerogels can tremendously enrich the electron-trapping sites through the generation of delocalized big π bonds. This work provides new insights into the understanding of polymer chemistry and photocatalysis mechanism.

A Layer-by-Layer Architecture for Printable Organic Solar Cells Overcoming the Scaling Lag of Module Efficiency

Summary To date, organic solar cells (OSCs) with the development of photovoltaic materials have realized high power conversion efficiencies (PCEs) through the solution processing strategy with bulk heterojunction (BHJ) structure, but the BHJ morphology is difficult to control in large-scale fabrication of OSCs. Herein, we report an alternative film-forming technology known as layer-by-layer (LbL). As compared to its BHJ counterpart, LbL presents many unique advantages including controllable “p-i-n” morphology, good charge transport and extraction properties, and great universality. By using the LbL-bladed coating strategy, a high PCE of 16.35% was achieved in the PM6:Y6 OSCs. Notably, a large-area solar module of 11.52 cm2 with a geometrical fill factor of over 90% exhibited an outstanding PCE of 11.86%, which represents the highest efficiency of large-area solar modules. The results may pave the way for the fabrication of the photoactive layer in the future industrial production of OSCs.

Influence of hydrogen and oxygen on the structure and properties of sputtered magnesium zirconium oxynitride thin films

Nitride materials with mixed ionic and covalent bonding character and resulting good charge transport properties are attractive for optoelectronic devices.

In-situ growth of CuO/Cu nanocomposite electrode for efficient CO2 electroreduction to CO with bacterial cellulose as support

Bacterial cellulose (BC) with large surface area and hydrophilic surface property is considered to be a good potential porous substrate for the deposition of active materials for catalysis, but lacks electrical conductivity for desired electrocatalysis application. By applying an in-situ chemical reduction, we here report a self-standing, BC-supported catalyst electrode of highly dispersed Cu and CuO nanocomposites (CuO/Cu4:3@BC) for catalyzing efficient CO2 electroreduction to CO. The inherent three-dimensional web-like porous structure of the BC substrate is sustained without further carbonization of the electrode. Compared to the conventional carbon paper-supported CuO/Cu composite catalysts, the as-prepared CuO/Cu4:3@BC electrode demonstrates an outstanding charge transport property and higher current density for CO2 reduction, owing to superiority of the web-like porous structure of the BC substrate with more accessible active sites to electrolytes and faster transfer of reactants and products. Therefore, the architecturally arranged CuO/Cu composite catalysts of the CuO/Cu4:3@BC electrode offer unique structural advantages of good ion and charge transport, promoting the catalytic kinetics for the conversion of CO2 to CO. The resulting electrode affords CO with a faradaic efficiency of 53 % at a small overpotential of 490 mV, and a durable activity over 40 h.

Co-catalyst-free photocatalytic hydrogen evolution by Laponite D clay

Laponite D is known as a zwitterionic synthetic clay having disc-shaped with negatively charged top faces and positively charged lateral edges, which is photochemically inactive and used to increase catalytic active surfaces. Herein, photocatalytic hydrogen evolution over Laponite D, which known as low cost inorganic clay, is firstly reported in a system containing Eosin-Y (EY) and triethanolamine (TEOA) as a photosensitizer and electron donor, respectively, under visible light illumination. This reaction system shows excellent stability due to the good charge transport and separation efficiency thanks to zwitterionic property of Laponite D.

Subtle Molecular Tailoring Induces Significant Morphology Optimization Enabling over 16% Efficiency Organic Solar Cells with Efficient Charge Generation.

Manipulating charge generation in a broad spectral region has proved to be crucial for nonfullerene-electron-acceptor-based organic solar cells (OSCs). 16.64% high efficiency binary OSCs are achieved through the use of a novel electron acceptor AQx-2 with quinoxaline-containing fused core and PBDB-TF as donor. The significant increase in photovoltaic performance of AQx-2 based devices is obtained merely by a subtle tailoring in molecular structure of its analogue AQx-1. Combining the detailed morphology and transient absorption spectroscopy analyses, a good structure-morphology-property relationship is established. The stronger π-π interaction results in efficient electron hopping and balanced electron and hole mobilities attributed to good charge transport. Moreover, the reduced phase separation morphology of AQx-2-based bulk heterojunction blend boosts hole transfer and suppresses geminate recombination. Such success in molecule design and precise morphology optimization may lead to next-generation high-performance OSCs.

Facilely fabricating FeSe nanoparticles embedded in N-doped carbon towards promoting sodium storage behaviors

Sodium ion battery (SIB) has been recognized as the successor to lithium ion battery (LIB) owing to its inherit feature of low cost and abundant resource. The commercial graphite anodes in LIB have been demonstrated unsuitable to accommodate Na+ due to the larger ionic radius than Li+. In this work, FeSe nanoparticles embedded in N-doped carbon (denoted as FeSe/N–C) are produced by one-step solid-phase process and explored as the potential anode candidate in SIB. Such composites exhibit high conductivity and special structural durability which provide good charge transport kinetics. As expected, the FeSe/N–C electrode displays high specific capacity, excellent rate performance and ultra-stable long-term cycling stability: it delivers a reversible capacity of 468.5 mAh g−1 at 0.5C rate, and 333.9 mAh g−1 for 800th cycle at 2.0C rate; more impressively, it exhibits a 235.9 mAh g−1 at 5.0C rate during the rate capability testing. This simple synthesis procedure may open up a way to engineer other metal selenide with carbonaceous modification agents for Na+-storage considering the cost-efficient and easy-scalability.

Novel Carbazole/Fluorene-Based Host Material for Stable and Efficient Phosphorescent OLEDs.

A novel host material of "M"-type carbazole/fluorene-based mDCzPF with a high triplet energy by utilizing meta-substituted phenyl groups as linkers was developed. It was demonstrated that the position of the substituents significantly affected the molecular configuration and dipole moment, which played a critical role in the device performances. Red phosphorescent OLED utilizing the "M"-type mDCzPF as the host represented a 10-fold operational lifetime improvement over the OLED using a "V"-type pDCzPF linked by para-substituted phenyl groups as the host because of the good charge transport ability of the mDCzPF. Additionally, the "M"-type mDCzPF host was also compatible with a blue emitting phosphorescent emitter PtNON. The PtNON-doped OLED using mDCzPF as the host exhibited a peak EQE of 18.3% with a small roll off, yet maintained an EQE of 13.3% at a high brightness of 5000 cd/m2. Thus, the novel "M"-type mDCzPF could be employed as stable host material for efficient OLED emitting across the whole visible spectrum. This study should provide a viable method for designing new host materials for the development of stable and efficient phosphorescent OLEDs.

Performance boosting strategy for perovskite light-emitting diodes

Low-dimensional (low-D) luminescent materials have attracted significant attention due to the high photoluminescent quantum yields. However, it is unclear whether low-D materials are superior to 3D materials for electroluminescent (EL) devices given that low-D materials have poor charge transport nature due to their highly localized electronic structures. We noticed a significant phenomenon that EL performances for 3D materials, such as CsPbX3, are governed by adjacent charge transport layers, which is possibly due to nonradiative recombination resulting from the small exciton binding energy. This finding encouraged us to develop new electron transport layers (ETLs) that satisfy not only the energy alignment to confine excitons but also an efficient electron injection into 3D CsPbX3 layers. This strategy enables one to exploit the good charge transport nature of 3D CsPbX3. The proposed amorphous Zn-Si-O ETL has sufficiently shallow electron affinity (∼3.2 eV) to confine excitons and sufficiently high electron mobility (∼0.8 cm2/V s) to transport electrons. Furthermore, the controllable conductivity and electron affinity of amorphous Zn-Si-O enable fine-tuning of charge balance. Consequently, the very low operating voltage of 2.9 V at 10 000 cd/m2 and high power efficiency of 33 lm/W were achieved for a green perovskite (CsPbBr3) EL (PeLED). The obtained ultrahigh brightness of ∼500 000 cd/m2 demonstrates the effectiveness of the proposed strategy. We also extend this strategy into 3D CsPbBrI2 (red) and 3D CsPbBrCl2 (blue) PeLEDs, and demonstrate a record high brightness of 20 000 cd/m2 for the red PeLED. We believe this study provides new insight into the realization of practical PeLEDs.

Free standing Si (Ge) nanowire/Cu nanowire composites as lithium ion battery anodes

Silicon (Si) and germanium (Ge) can alloy with lithium to achieve high theoretical specific capacities (3579 mAh/g for Li15Si4 and 1384 mAh/g for Li15Ge4), which are several times greater than commercial graphite (372 mAh/g). However, they exhibit significant volume and crystal structural change during cycling processes, leading to structural pulverization and loss of electrical conduction paths between individual active materials and current collector. We report a non-carbon based free standing electrodes fabricated by directly mixing Si and Ge nanowires with Cu nanowires as lithium ion battery anodes. The one dimensional nanostructure of Si (Ge) and Cu provide good charge transport along their length and many contact points were formed between NWs after annealing process. The nanowire composites have several advantages compared to the conventional electrode that slurry materials are coated on a metal foil. For example, the weight is lighter than conventional electrodes because it does not need a current collector and is fabricated without any additives, and binders. Moreover, the space among the nanowires can accommodate the volume contraction of Si (Ge) during alloying and dealloying process and enhance the electrolyte penetration.

Construction of heterostructured g-C3N4@TiATA/Pt composites for efficacious photocatalytic hydrogen evolution

Construction of heterostructured photocatalysts is a feasible method for improving hydrogen production from water splitting because of its good charge transport efficiency. Herein, we coupled the Ti-MOFs (TiATA) with metal-free graphitic carbon nitride (g-C3N4) to synthesize composites, g-C3N4@TiATA, in which a heterostructure was formed between g-C3N4 and TiATA. The establishment of heterojunctions not only broadens the light absorption range of g-C3N4@TiATA (490 nm) by contrast with g-C3N4 (456 nm), but also greatly accelerates charge migration. Photocatalytic studies present that the construction of heterostructure steering the charges flow from g-C3N4 to TiATA and then delivery to the cocatalyst of Pt nanoparticles, exhibiting an impressively photocatalytic hydrogen production rate (265.8 μmol·h−1) in assistance of 300 W Xenon lamp, which is about 3.4 times as much as g-C3N4/Pt.