Micro-Cup Architecture for Printing and Coating Asymmetric 2d-Material-Based Solid-State Supercapacitors.

High energy density micro-supercapacitors (MSCs) are in high demand for miniaturized electronics and microsystems. Research efforts today focus on materials development, applied in the planar interdigitated, symmetric electrode architecture. A novel "cup & core" device architecture that allows for printing of asymmetric devices without the need of accurately positioning the second finger electrode here have been introduced. The bottom electrode is either produced by laser ablation of a blade-coated graphene layer or directly screen-printed with graphene inks to create grids with high aspect ratio walls forming an array of "micro-cups". A quasi-solid-state ionic liquid electrolyte is spray-deposited on the walls; the top electrode material -MXene inks- is then spray-coated to fill the cup structure. The architecture combines the advantages of interdigitated electrodes for facilitated ion-diffusion, which is critical for 2D-material-based energy storage systems by providing vertical interfaces with the layer-by-layer processing of the sandwich geometry. Compared to flat reference devices, volumetric capacitance of printed "micro-cups" MSC increased considerably, while the time constant decreased (by 58%). Importantly, the high energy density (3.99 µWh cm-2 ) of the "micro-cups" MSC is also superior to other reported MXene and graphene-based MSCs.

Superweak Coordinating Anion as Superstrong Enhancer of Cyanine Organic Semiconductor Properties.

The superweak tetrakis(nonafluoro-tert-butoxy)aluminate coordinating anion was employed to introduce pseudo-gas-phase conditions to the 2-[5-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3-pentadien-1-yl]-1,3,3-trimethyl-3H-indolium chromophore. The resulting formation of a photoactive organic-inorganic hybrid salt has led to a highly stabilized excited state of the organic chromophore mainly due to the minimized lattice energy and Coulomb interactions. These highly beneficial features caused by the well dispersed negative charge of the anion have led to an enhanced neat spin-casted film fluorescence intensity, prolonged fluorescence lifetime, smooth thin film surfaces and a record power photovoltaic efficiency of 3.8 % when compared to organic salts of this particular chromophore containing anions with localised negative charge. Clear evidence is given that a superweak coordinating anion is an emerging key parameter in cyanine dye photochemistry. This approach can be seen as a general guideline to prepare highly efficient ionic dyes for organic semiconductor applications.

Cyanine platelet single crystals: growth, crystal structure and optical spectra.

Crystalline organic semiconducting materials are much in demand for multiple electronic and optoelectronic device applications. Here, solution grown ultrathin rhombic crystals of a trimethine carbocyanine anionic dye are used to establish relationships between structural and optical properties. The dye crystallized in the monoclinic space group P21/c featuring alternating layers of molecules in two different herringbone type patterns, with perchlorate counterions located mostly within one of the two layers. Micro transmittance spectroscopy revealed a broadened spectrum compared to those obtained in solution and in an amorphous thin film. Using polarized light, transmission spectroscopy revealed strong low-energy and weak high-energy bands polarized along the crystallographic b- and c-axis, respectively. Using the extended dipole approximation, significant exciton couplings are predicted between neighboring molecules in the crystal, of the order of the intrinsic monomer reorganization energies associated with nuclear relaxation after excitation, depicting a complex spectral scenario. The exciton coupling pattern explains the relative energies of the b- and c-polarized components but the observed intensities are opposite to expectations based on chromophore alignment within the crystal.

Insights into photovoltaic properties of ternary organic solar cells from phase diagrams.

The efficiency of ternary organic solar cells relies on the spontaneous establishment of a nanostructured network of donor and acceptor phases during film formation. A fundamental understanding of phase composition and arrangement and correlations to photovoltaic device parameters is of utmost relevance for both science and technology. We demonstrate a general approach to understanding solar cell behavior from simple thermodynamic principles. For two ternary blend systems we construct and model phase diagrams. Details of EQE and solar cell parameters can be understood from the phase behavior. Our blend system is composed of PC70BM, PBDTTT-C and a near-infrared absorbing cyanine dye. Cyanine dyes are accompanied by counterions, which, in a first approximation, do not change the photophysical properties of the dye, but strongly influence the morphology of the ternary blend. We argue that counterion dissociation is responsible for different mixing behavior. For the dye with a hexafluorophosphate counterion a hierarchical morphology develops, the dye phase separates on a large scale from PC70BM and cannot contribute to photocurrent. Differently, a cyanine dye with a TRISPHAT counterion shows partial miscibility with PC70BM. A large two-phase region dictated by the PC70BM: PBDTTT-C mixture is present and the dye greatly contributes to the short-circuit current.

Ternary semitransparent organic solar cells with a laminated top electrode.

Tinted and colour-neutral semitransparent organic photovoltaic elements are of interest for building-integrated applications in windows, on glass roofs or on facades. We demonstrate a semitransparent organic photovoltaic cell with a dry-laminated top electrode that achieves a uniform average visible transmittance of 51% and a power conversion efficiency of 3%. The photo-active material is based on a majority blend composed of a visibly absorbing donor polymer and a fullerene acceptor, to which a selective near-infrared absorbing cyanine dye is added as a minority component. Our results show that organic ternary blends are attractive for the fabrication of semitransparent solar cells in general, because a guest component with a complementary absorption can compensate for the inevitably reduced current generation capability of a high-performing binary blend when applied as a thin, semitransparent film.

Influence of chemically p-type doped active organic semiconductor on the film thickness versus performance trend in cyanine/C60 bilayer solar cells.

Simple bilayer organic solar cells rely on very thin coated films that allow for effective light absorption and charge carrier transport away from the heterojunction at the same time. However, thin films are difficult to coat on rough substrates or over large areas, resulting in adverse shorting and low device fabrication yield. Chemical p-type doping of organic semiconductors can reduce Ohmic losses in thicker transport layers through increased conductivity. By using a Co(III) complex as chemical dopant, we studied doped cyanine dye/C60 bilayer solar cell performance for increasing dye film thickness. For films thicker than 50 nm, doping increased the power conversion efficiency by more than 30%. At the same time, the yield of working cells increased to 80%. We addressed the fate of the doped cyanine dye, and found no influence of doping on solar cell long term stability.

Multifunctional SnO2 QDs/MXene Heterostructures as Laminar Interlayers for Improved Polysulfide Conversion and Lithium Plating Behavior.

Poor cycling stability in lithium-sulfur (Li-S) batteries necessitates advanced electrode/electrolyte design and innovative interlayer architectures. Heterogeneous catalysis has emerged as a promising approach, leveraging the adsorption and catalytic performance on lithium polysulfides (LiPSs) to inhibit LiPSs shuttling and improve redox kinetics. In this study, we report an ultrathin and laminar SnO2@MXene heterostructure interlayer (SnO2@MX), where SnO2 quantum dots (QDs) are uniformly distributed across the MXene layer. The combined structure of SnO2 QDs and MXene, along with the creation of numerous active boundary sites with coordination electron environments, plays a critical role in manipulating the catalytic kinetics of sulfur species. The Li-S cell with the SnO2@MX-modified separator not only demonstrates superior electrochemical performance compared to cells with a bare separator but also induces homogeneous Li deposition during cycling. As a result, an areal capacity of 7.6 mAh cm-2 under a sulfur loading of 7.5 mg cm-2 and a high stability over 500 cycles are achieved. Our work demonstrates a feasible strategy of utilizing a laminar separator interlayer for advanced Li-S batteries awaiting commercialization and may shed light on the understanding of heterostructure catalysis with enhanced reaction kinetics.

Unraveling Polysulfide's Adsorption and Electrocatalytic Conversion on Metal Oxides for Li-S Batteries.

Lithium sulfur (LiS) batteries possess high theoretical capacity and energy density, holding great promise for next generation electronics and electrical vehicles. However, the LiS batteries development is hindered by the shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPSs). Designing highly polar materials such as metal oxides (MOs) with moderate adsorption and effective catalytic activity is essential to overcome the above issues. To design efficient MOs catalysts, it is critical and necessary to understand the adsorption mechanism and associated catalytic processes of LiPSs. However, most reviews still lack a comprehensive investigation of the basic mechanism and always ignore their in-depth relationship. In this review, a systematic analysis toward understanding the underlying adsorption and catalytic mechanism in LiS chemistry as well as discussion of the typical works concerning MOs electrocatalysts are provided. Moreover, to improve the sluggish "adsorption-diffusion-conversion" process caused by the low conductive nature of MOs, oxygen vacancies and heterostructure engineering are elucidated as the two most effective strategies. The challenges and prospects of MOs electrocatalysts are also provided in the last section. The authors hope this review will provide instructive guidance to design effective catalyst materials and explore practical possibilities for the commercialization of LiS batteries.

Stable MXene Dough with Ultrahigh Solid Fraction and Excellent Redispersibility toward Efficient Solution Processing and Industrialization.

Two-dimensional (2D) transition metal carbides, and/or nitrides, so-called MXenes, have triggered intensive research interests in applications ranging from electrochemical energy storage to electronics devices. Producing these functional devices by printing necessitates to match the rheological properties of MXene dispersions to the requirements of various solution processing techniques. In particular, for additive manufacturing such as extrusion-printing, MXene inks with high solid fraction are typically required, which is commonly achieved by tediously removing excessive free water (top-down route). Here, the study reports on a bottom-up route to reach a highly concentrated binary MXene-water blend, so-called MXene dough, by controlling the water admixture to freeze-dried MXene flakes by exposure to water mist. The existence of a critical threshold of MXene solid content (≈60%), beyond which no dough is formed, or formed with compromised ductility is revealed. Such metallic MXene dough possesses high electrical conductivity, excellent oxidation stability, and can withstand a couple of months without apparent decay, providing that the MXene dough is properly stored at low-temperature with suppressed dehydration environment. Solution processing of the MXene dough into a micro-supercapacitor with gravimetric capacitance of 161.7 F g-1 is demonstrated. The impressive chemical and physical stability/redispersibility of MXene dough indicate its great promise in future commercialization.

Rational Design of Ti3C2Tx MXene Inks for Conductive, Transparent Films.

Transparent conductive electrodes (TCEs) with a high figure of merit (FOMe, defined as the ratio of transmittance to sheet resistance) are crucial for transparent electronic devices, such as touch screens, micro-supercapacitors, and transparent antennas. Two-dimensional (2D) titanium carbide (Ti3C2Tx), known as MXene, possesses metallic conductivity and a hydrophilic surface, suggesting dispersion stability of MXenes in aqueous media allowing the fabrication of MXene-based TCEs by solution processing. However, achieving high FOMe MXene TCEs has been hindered mainly due to the low intrinsic conductivity caused by percolation problems. Here, we have managed to resolve these problems by (1) using large-sized Ti3C2Tx flakes (∼12.2 µm) to reduce interflake resistance and (2) constructing compact microstructures by blade coating. Consequently, excellent optoelectronic properties have been achieved in the blade-coated Ti3C2Tx films, i.e., a DC conductivity of 19 325 S cm-1 at transmittances of 83.4% (≈6.7 nm) was obtained. We also demonstrate the applications of Ti3C2Tx TCEs in transparent Joule heaters and the field of supercapacitors, showing an outstanding Joule heating effect and high rate response, respectively, suggesting enormous potential applications in flexible, transparent electronic devices.

Aerosol Jet Printing of 3D Pillar Arrays from Photopolymer Ink.

An aerosol jet printing (AJP) printing head built on top of precise motion systems can provide positioning deviation down to 3 µm, printing areas as large as 20 cm × 20 cm × 30 cm, and five-axis freedom of movement. Typical uses of AJP are 2D printing on complex or flexible substrates, primarily for applications in printed electronics. Nearly all commercially available AJP inks for 2D printing are designed and optimized to reach desired electronic properties. In this work, we explore AJP for the 3D printing of free-standing pillar arrays. We utilize aryl epoxy photopolymer as ink coupled with a cross-linking "on the fly" technique. Pillar structures 550 µm in height and with a diameter of 50 µm were 3D printed. Pillar structures were characterized via scanning electron microscopy, where the morphology, number of printed layers and side effects of the AJP technique were investigated. Satellite droplets and over-spray seem to be unavoidable for structures smaller than 70 µm. Nevertheless, reactive ion etching (RIE) as a post-processing step can mitigate AJP side effects. AJP-RIE together with photopolymer-based ink can be promising for the 3D printing of microstructures, offering fast and maskless manufacturing without wet chemistry development and heat treatment post-processing.

A Universal Approach for Room-Temperature Printing and Coating of 2D Materials.

Processing 2D materials into printable or coatable inks for the fabrication of functional devices has proven to be quite difficult. Additives are often used in large concentrations to address the processing challenges, but they drastically degrade the electronic properties of the materials. To remove the additives a high-temperature post-deposition treatment can be used, but this complicates the fabrication process and limits the choice of materials (i.e., no heat-sensitive materials). In this work, by exploiting the unique properties of 2D materials, a universal strategy for the formulation of additive-free inks is developed, in which the roles of the additives are taken over by van der Waals (vdW) interactions. In this new class of inks, which is termed "vdW inks", solvents are dispersed within the interconnected network of 2D materials, minimizing the dispersibility-related limitations on solvent selection. Furthermore, flow behavior of the inks and mechanical properties of the resultant films are mainly controlled by the interflake vdW attractions. The structure of the vdW inks, their rheological properties, and film-formation behavior are discussed in detail. Large-scale production and formulation of the vdW inks for major high-throughput printing and coating methods, as well as their application for room-temperature fabrication of functional films/devices are demonstrated.

Template synthesis of cyanine dye H-aggregates on nanostructured [6,6]-phenyl C61-butyric acid methyl ester substrates.

A novel and general method for the synthesis of H-aggregates is presented. H-aggregates can be precipitated from solutions of cyanine dyes in nanostructured [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM) template films. H-aggregates synthesized that way have a narrow line shape width comparable to the smallest H-bands reported for thin films so far. We demonstrate that H-aggregates can be induced in different cyanine dyes (trimethine-, pentamethine- and heptamethine dyes). Aggregation follows a universal pathway, the concentration dependence of aggregation for different dyes can be scaled to fall onto one master curve. According to our model, H-aggregates have the form of 3D-crystals that form within cavities of the template. The template substrate is fabricated by means of a phase separation process of PCBM with a specific cyanine dye and consecutive selective dissolution of the dye. The dimensions of the template cavities have a major influence on aggregation.

Enhanced Room-Temperature Photoluminescence Quantum Yield in Morphology Controlled J-Aggregates.

Supramolecular assemblies from organic dyes forming J-aggregates are known to exhibit narrowband photoluminescence with full-width at half maximum of ≈9 nm (260 cm-1). Applications of these high color purity emitters, however, are hampered by the rather low photoluminescence quantum yields reported for cyanine J-aggregates, even when formed in solution. Here, it is demonstrated that cyanine J-aggregates can reach an order of magnitude higher photoluminescence quantum yield (increase from 5% to 60%) in blend solutions of water and alkylamines at room temperature. By means of time-resolved photoluminescence studies, an increase in the exciton lifetime as a result of the suppression of non-radiative processes is shown. Small-angle neutron scattering studies suggest a necessary condition for the formation of such highly emissive J-aggregates: the presence of a sharp water/amine interface for J-aggregate assembly and the coexistence of nanoscale-sized water and amine domains to restrict the J-aggregate size and solubilize monomers, respectively.

Fast assembly of cyanine dyes into aggregates onto [6,6]-phenyl C61-butyric acid methyl ester surfaces from organic solvents.

Supramolecular agglomerates of organic colorants based on noncovalent interactions are promising candidates for the development of sensors, optoelectronics, lighting, or photovoltaics. However, their fast and defect-free fabrication on large scales using low-cost technologies has proven elusive so far. Here, we introduce a so far unreported mechanism to induce molecular order in cyanine dyes within minutes from organic solvents by self-assembly. Spin coating blends of a cyanine dye and a soluble fullerene derivative ([6,6]-phenyl C(61)-butyric acid methyl ester (PCBM)) from apolar, aprotic solvents leads to phase-separated structures on the micrometer scale. With this superordinated phase structure, adjustment of dye aggregation is possible, leading to novel optical properties of the film emerging from dye self-assembly on the nanometer scale. In the primary process, semiporous PCBM domains act as nucleation sites for H-aggregates. H-aggregates can then be reconstructed into J-aggregates by dissolving PCBM from the film. Unexpectedly, the method even works for sterically hindered cyanine dyes that are known for their reduced tendency to aggregate. Additionally, selective removal of H-aggregates leaves a template of PCBM nanocrystals, onto which cyanine dye monomers readsorb from solution, forming H-aggregates of similar quality.

Turning Trash into Treasure: Additive Free MXene Sediment Inks for Screen-Printed Micro-Supercapacitors.

Printed functional conductive inks have triggered scalable production of smart electronics such as energy-storage devices, antennas, wearable electronics, etc. Of particular interest are highly conductive-additive-free inks devoid of costly postdeposition treatments to eliminate sacrificial components. Due to the high filler concentration required, formulation of such waste-free inks has proven quite challenging. Here, additive-free, 2D titanium carbide MXene aqueous inks with appropriate rheological properties for scalable screen printing are demonstrated. Importantly, the inks consist essentially of the sediments of unetched precursor and multilayered MXene, which are usually discarded after delamination. Screen-printed structures are presented on paper with high resolution and spatial uniformity, including micro-supercapacitors, conductive tracks, integrated circuit paths, and others. It is revealed that the delaminated nanosheets among the layered particles function as efficient conductive binders, maintaining the mechanical integrity and thus the metallic conductive network. The areal capacitance (158 mF cm-2 ) and energy density (1.64 µWh cm-2 ) of the printed micro-supercapacitors are much superior to other devices based on MXene or graphene. The ink formulation strategy of "turning trash into treasure" for screen printing highlights the potential of waste-free MXene sediment printing for scalable and sustainable production of next-generation wearable smart electronics.

Nanocellulose-MXene Biomimetic Aerogels with Orientation-Tunable Electromagnetic Interference Shielding Performance.

Designing lightweight nanostructured aerogels for high-performance electromagnetic interference (EMI) shielding is crucial yet challenging. Ultrathin cellulose nanofibrils (CNFs) are employed for assisting in building ultralow-density, robust, and highly flexible transition metal carbides and nitrides (MXenes) aerogels with oriented biomimetic cell walls. A significant influence of the angles between oriented cell walls and the incident EM wave electric field direction on the EMI shielding performance is revealed, providing an intriguing microstructure design strategy. MXene "bricks" bonded by CNF "mortars" of the nacre-like cell walls induce high mechanical strength, electrical conductivity, and interfacial polarization, yielding the resultant MXene/CNF aerogels an ultrahigh EMI shielding performance. The EMI shielding effectiveness (SE) of the aerogels reaches 74.6 or 35.5 dB at a density of merely 8.0 or 1.5 mg cm-3, respectively. The normalized surface specific SE is up to 189 400 dB cm2 g-1, significantly exceeding that of other EMI shielding materials reported so far.

Excitonic channels from bio-inspired templated supramolecular assembly of J-aggregate nanowires.

Supramolecular assemblies with controlled morphology are of paramount importance for energy transport in organic semiconductors. Despite considerable freedom in molecular design, the preparation of dyes that form one dimensional J-aggregates is challenging. Here, we demonstrate a simple and effective route to functionalize dendronized polymers (DPs) with J-aggregates to construct tubular DP/J-aggregate nanowires. When J-aggregates are adsorbed onto DPs anchored to glass substrates, they assemble into microcrystalline domains typical for J-aggregates adsorbed on functionalized surfaces. Differently, the complexation between the dendronized polymer and J-aggregates in solution leads to dense packing of J-aggregate strands on the periphery of the DPs. Using a layer-by-layer (LBL) technique, DPs loaded with J-aggregates can also be adsorbed onto a DP monolayer. In this case, the thin film absorption spectra are narrower and indicate higher ratios of J-aggregate to monomer and dimer absorption than bare J-aggregates deposited similarly. The demonstration of J-aggregate adsorption on filamentous polymeric templates is a promising step toward artificial 1D light harvesting antennas, with potential applications in opto-electronic devices.

Increasing Photovoltaic Performance of an Organic Cationic Chromophore by Anion Exchange.

A symmetrical cyanine dye chromophore is modified with different counteranions to study the effect on crystal packing, polarizability, thermal stability, optical properties, light absorbing layer morphology, and organic photovoltaic (OPV) device parameters. Four sulfonate-based anions and the bulky bistriflylimide anion are introduced to the 2-[5-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)-1,3-pentadien-1-yl]-1,3,3-trimethyl-3H-indolium chromophore using an Amberlyst A26 (OH- form) anion exchanger. Anionic charge distribution clearly correlates with device performance, whereby an average efficiency of 2% was reached in a standard bilayer organic solar. Evidence is given that the negative charge of the anion distributed over a large number of atoms is significantly more important than the size of the organic moieties of the sulfonate charge carrying group. This provides a clear strategy for future design of more efficient cyanine dyes for OPV applications.

Towards cancer cell-specific phototoxic organometallic rhenium(I) complexes.

Over the recent years, several Re(I) organometallic compounds have been shown to be toxic to various cancer cell lines. However, these compounds lacked sufficient selectivity towards cancer tissues to be used as novel chemotherapeutic agents. In this study, we probe the potential of two known N,N-bis(quinolinoyl) Re(I) tricarbonyl complex derivatives, namely Re(I) tricarbonyl [N,N-bis(quinolin-2-ylmethyl)amino]-4-butane-1-amine (Re-NH2) and Re(I) tricarbonyl [N,N-bis(quinolin-2-ylmethyl)amino]-5-valeric acid (Re-COOH), as photodynamic therapy (PDT) photosensitizers. Re-NH2 and Re-COOH proved to be excellent singlet oxygen generators in a lipophilic environment with quantum yields of about 75%. Furthermore, we envisaged to improve the selectivity of Re-COOH via conjugation to two types of peptides, namely a nuclear localization signal (NLS) and a derivative of the neuropeptide bombesin, to form Re-NLS and Re-Bombesin, respectively. Fluorescent microscopy on cervical cancer cells (HeLa) showed that the conjugation of Re-COOH to NLS significantly enhanced the compound's accumulation into the cell nucleus and more specifically into its nucleoli. Importantly, in view of PDT applications, the cytotoxicity of the Re complexes and their bioconjugates increased significantly upon light irradiation. In particular, Re-Bombesin was found to be at least 20-fold more toxic after light irradiation. DNA photo-cleavage studies demonstrated that all compounds damaged DNA via singlet oxygen and, to a minor extent, superoxide production.