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Large-area flexible transparent conductive electrodes (TCEs) featuring excellent optoelectronic properties (low sheet resistance, Rs, at high transparency, T) are vital for integration in transparent wearable electronics (i.e., antennas, sensors, supercapacitors, etc.). Solution processing (i.e., printing and coating) of conductive inks yields highly uniform TCEs at low cost, holding great promise for commercially manufacturing of transparent electronics. However, to formulate such conductive inks as well as to realize continuous conductive films in the absence of percolation issue are quite challenging. Herein, the scalable slot-die coating of Ti3C2Tx MXene aqueous inks is reported for the first time to yield large-area uniform TCEs with outstanding optoelectronic performance, that is, average DC conductivity of 13 000 ± 500 S cm−1. The conductive MXene nanosheets are forced to orientate horizontally as the inks are passing through the moving slot, leading to the rapid manufacturing of highly aligned MXene TCEs without notorious percolation problems. Moreover, through tuning the ink formulations, such conductive MXene films can be easily adjusted from transparent to opaque as required, demonstrating very low surface roughness and even mirror effects. These high-quality, slot-die-coated MXene TCEs also demonstrate excellent electrochemical charge storage properties when assembled into supercapacitors., Advanced Functional Materials, 33 (15), ISSN:1616-3028, ISSN:1616-301X

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.

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.

Carbon-based hole transport layer-free carbon mesoscopic perovskite solar cells (MPSCs) are considered to be cell architectures with high potential for commercialization, due to their enhanced stability. In the standard process for large area and module fabrication, mesoporous layers of TiO2, ZrO2 and carbon are screen printed onto fluorine doped tin oxide (FTO) coated with a compact TiO2 (cTiO2) layer. In this work, we sequentially replaced screen printing by slot die coating one by one for all layers until we achieved a fully slot die coated solar cell. Slot die coating is a manufacturing technique with a much higher throughput than screen printing. We demonstrate that slot die coated layers need not be sintered separately as opposed to the screen printed layers, but can rather be co-fired for increased manufacturing speed and efficacy. We characterize the inks, coating process, morphology and performance of these solar cells. The cells show efficiencies comparable to those of the screen printed control devices. The cells also show extraordinarily high shelf life stability. We also demonstrate that ellipsometry can be used as an efficient (in-situ) tool to characterize the stack structure of the cells.

Customizable solar cells are required for aesthetic indoor and outdoor photovoltaic deployment as well as for the freedom of design of small and portable power supplies. We demonstrate that drop on demand inkjet printing can be used for the fabrication of monolithic mesoscopic carbon-based perovskite solar cells by printing all of the oxide layers in the stack as well as the organo-metal halide absorber. Printable inks using environmentally friendly solvents and jetting parameters were developed in order to achieve homogenous and continuous functional layers of the photovoltaic stack. Inkjet printed cells are compared to those obtained from the standard screen-printing route. As a proof of principle, photovoltaic cells with an area of 1.5 cm2 and a performance of 9.1% were realized by inkjet printing, which opens up intriguing application possibilities.

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., Advanced Materials, 34 (4), ISSN:0935-9648, ISSN:1521-4095

In this paper, some practical issues related to the manufacturing, and design criteria related to the application in devices of a hybrid silver grid/poly (3,4-ethylenedioxythiophene) semi-transparent electrode are discussed. The electrodes are fabricated by gravure printing and screen printing. Experiments showed that defects in the printed grid due to imperfect ink transfer from the gravure roll to the substrate are detrimental to electrode performance. Various parameters like gravure cell design, printing speed, or particle size of the ink were investigated to minimize the fraction of defects and to obtain highly conductive grids. It will be demonstrated that overprinting of the lines is a feasible strategy to minimize the number of defects without noticeably broadening the lines. While a defect-free grid is prerequisite for such a hybrid device, for applications even stronger design criteria hold. That is addressed in the second part of the paper, where the electrical properties of the printed grids are simulated. With two exemplary device architectures, namely an organic light-emitting diode (OLED) and an organic photovoltaic cell, artificial load layers are integrated into the device structure, and potential maps are calculated. The examples show how simulations can be deployed to design and optimize grid electrodes for a specific application.

A symmetrical trimethine indocyanine dye chromophore was modified with the bistriflylimide anion to study the changes in Coulomb interactions, thermal stability and the volatility of the organic salt. The bulky bistriflylimide anion minimizes electrostatic interactions and increases the vapour pressure of the compound resulting in an increased volatility of the organic salt. First examples of entirely vacuum-processed bulk heterojunction organic photovoltaic devices show the proof of concept. We give evidence that the well dispersed negative charge of the bistriflylimide introduces quasi gas phase conditions to the cyanine chromophore. This overcomes the existing restriction of thin film formation via spincasting in cyanine dye based organic electronics and expands the thin film fabrication process choices towards physical vapour deposition.

Narrowband photodetectors are useful for a myriad of applications involving color discrimination as well as biological imaging and machine vision. Prevalent devices use broadband light absorbing materials in conjunction with electric (charge collection narrowing, photo multiplication) and optical strategies (optical cavity) to narrow down the spectral response of the detector. Here we exploit the intrinsic narrow absorption width of ∼13–50 nm peculiar to J-aggregates of strongly coupled cyanine dye molecules for narrowband photodetectors. Albeit using ultrathin J-aggregate films (10 nm) the unparalleled optical aggregate properties lead to high external quantum efficiency (15%) and response speed (15 kHz) at low bias voltage (−1 V). We show that the self-assembly process and device architecture used permit the incorporation of J-aggregates of various cyanine dyes with photodetection maxima ranging from the visible to the near-infrared region up to 1000 nm. Narrow bandwidth (

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.

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 cm(2) g(-1), significantly exceeding that of other EMI shielding materials reported so far., Advanced Science, 7 (15), ISSN:2198-3844

Rechargeable lithium-sulfur (Li-S) batteries have attracted significant research attention due to their high capacity and energy density. However, their commercial applications are still hindered by challenges such as the shuttle effect of soluble lithium sulfide species, the insulating nature of sulfur, and the fast capacity decay of the electrodes. Various efforts are devoted to address these problems through questing more conductive hosts with abundant polysulfide chemisorption sites, as well as modifying the separators to physically/chemically retard the polysulfides migration. Two dimensional transition metal carbides, carbonitrides and nitrides, so-called MXenes, are ideal for confining the polysulfides shuttling effects due to their high conductivity, layered structure as well as rich surface terminations. As such, MXenes have thus been widely studied in Li-S batteries, focusing on the conductive sulfur hosts, polysulfides interfaces, and separators. Therefore, in this review, we summarize the significant progresses regarding the design of multifunctional MXene-based Li-S batteries and discuss the solutions for improving electrochemical performances in detail. In addition, challenges and perspectives of MXenes for Li-S batteries are also outlined. image

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.

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.

Light-emitting electrochemical cells (LECs) can be fabricated as a single emissive organic/salt layer sandwiched between two electrodes, offering cost-effective next generation signage and lighting applications. Cyanine dyes are especially attractive to exploit the low cost potential of LECs. Cyanines denote a large class of fluorescent organic salts with tuneable emission wavelength, inherent conductivity for ionic and electronic charges, and many cyanines are commercially available at low cost. We systematically tested a set of cyanine dyes for visible emitting LECs. To circumvent non-radiative quenching processes in pure cyanine films (monomer fluorescence quantum yields, PLQE

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. ISSN:1468-6996 ISSN:1878-5514

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.

Electrohydrodynamic lithography (EHDL) is a parallel patterning process which typically makes use of topographically structured electrodes to guide pattern formation along areas of higher electrical field strength. The main driving force for pattern formation is an electrostatic pressure acting on a thin film polymer surface caused by a voltage applied between a top and bottom electrode. We here demonstrate that the principle can be applied using an addressable electrode composed of interdigitated fingers. Depending on the applied voltages, line patterns with different periodicities were fabricated. Our proof-of-concept experiments pave the way for a parallel pattern replication process where a serially addressed master is used. We complement the experiments by modelling the potentials across the electrodes and electrostatic forces acting on the polymer surface using different addressing schemes. Numerical simulations of the experimental setup pointed to some critical issues we experienced during the design of the experiments.

Photoinduced electron transfer in light-absorbing materials is the first step towards charge separation and extraction in small molecule-based organic solar cells. The excited state dynamics of the cyanine dye cation Cy3 paired with a tetraphenylborate counter-anion (Cy3-B) was studied in pristine solid-state films of the dye and in blends with the electron acceptor material PCBM. Here we show that photoexcited Cy3-B in pure films undergoes intra-ion pair reductive quenching on the picosecond time scale, while in blends with PCBM sub-picosecond formation of the Cy3 oxidized species is observed upon electron injection from the dye excited state into the fullerene. Kinetic competition between light-induced electron- and hole transfer processes strongly depends on the PCBM content in the blends. A high PCBM loading produces a fully intermixed phase, where the cyanine oxidized states appear on ultrashort (

The combination of Time-of-flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Scanning Force Microscopy (SFM) allows the 3D-compositional analysis of samples or devices. Typically, the topographical data obtained by SFM is used to determine the initial sample topography and the absolute depth of the ToF-SIMS analysis. Here ToF-SIMS and SFM data sets obtained on 2 prototypical samples are explored to go beyond conventional 3D-compositional analysis. SFM topographical and material contrast maps are combined with ToF-SIMS retrospective analysis to detect features that would have escaped a conventional ToF-SIMS data analysis. In addition, SFM data is used to extrapolate the chemical information beyond the spatial resolution of ToF-SIMS, allowing the mapping of the chemical composition at the nanoscale.

Tailoring hematite thin film nanostructure is particularly interesting since this oxide`s function is closely related to its structure, for example when implemented as a photoanode in water splitting solar cells. In this study, electrohydrodynamic destabilization was designed to grow hematite nanodroplets with morphologies controlled by a master electrode. A polymer/iron salt film was destabilized by electrohydrodynamic destabilization and the resulting structures were pyrolysed to achieve crystalline a-Fe203 nanodroplets of 30 nm height and 70 nm radius. NEXAFS spectroscopy proved that the structures contain ferrihydrite, which is converted into hematite during pyrolysis, while the polymer was decomposed. Homogeneous nanoparticle precipitation in the bulk of the polymer, due to encapsulation of the iron precursor in the polymer matrix, is accounted for the good preservation of the structures. This study represents the first step towards the use of electrohydrodynamic destabilization for nanostructuring of hematite thin films, with a control over the feature size. (C) 2014 Elsevier B.V. All rights reserved.

Thin films involving an oxide heterojunction are increasingly employed as electrodes for solar water splitting in photoelectrochemical cells. Hematite (α-Fe2O3) and tungsten oxide form an attractive heterojunction for this purpose. A major limitation of this strategy is the short charge carrier diffusion length in hematite. Ultra-thin films were implemented to address this low conductivity issue. Nevertheless, such ultrathin films do not absorb light efficiently. The present study explores light trapping strategies to increase the optical path length of photons in hematite. Vesicle suspensions were developed to obtain thin films composed of a microspheroid array with a tungsten oxide core and a nanometer sized hematite overlayer. This bottom-up approach allows a fine control of the spheroid dimensions at the micrometric to the submicrometric scale. Using the finite difference time domain method, light propagation inside the microstructures was quantitatively simulated. The simulation results were coupled to an analysis of the photoelectrochemical response of the films. Experiments and simulation show quantitative agreement and bring important insights into the relationship between the interaction of light with the microstructure and the photoanode performance.

C-60 fullerene derivatives bearing aliphatic chains can self-assemble into versatile supramolecular structures. Cross-linking of such self-assembled morphologies is an attractive approach to enhance the structural stability of these self-organized structures. We describe the synthesis of a C-60 fimctionalized with a single alkyl chain bearing a diacetylene moiety. In a thin film, the molecule self-assembles into lamellar arrays. The character of the side chain attached to the fullerene is key to the observed packing ability. The stabilization proceeds through solid-state polymerization of the diacetylene moieties. By blending the fiillerene derivative with a cyanine dye, various nanostructured fiillerene morphologies are obtained that can be selectively stabilized by thermal polymerization. These films can serve as basis for nanostructured fullerene scaffolds that can find applications in optics and electronics.

Studying and understanding the conditions under which organic semiconductors can be engineered to form aligned single crystals in thin films is of primary importance owing to their unique orientation-dependent optoelectronic properties. Efforts to reach this goal by self-assembly from solution-processed films have been rewarded only with limited success. In this article we present a new method to grow single crystalline thin films via solvent annealing. We identify solvate crystal growth in combination with a specific film dewetting morphology as key to successful fabrication of single crystals. Furthermore, these 2D single crystals can align on chemically patterned substrates to minimize their interfacial energy. We explore in situ the conditions for crystal formation and alignment.

Squaraine (SQ) dye-based organic semiconductor hybrids 6T-SQ and 18T-SQ functionalized with oligothiophene dendrons were synthesized via Suzuki–Miyaura coupling. The electronic coupling between the oligothiophene dendrons and the squaraine core was rather weak, as suggested from UV–vis spectra, cyclic voltammetry measurements and molecular modeling. Thin films of pure SQ were characterized by a pronounced solvent- and heat-induced crystallization tendency. The dendrons substantially hindered the squaraine core crystallization, and 18T-SQ films remained amorphous after annealing or storage for several weeks. PCBM disrupted dye crystallization in blends, and smooth and stable films could be coated. Heat treatment of blended films induced dewetting for SQ:PCBM and 6T-SQ:PCBM, but 18T-SQ:PCBM remained again stable. These morphological film features could consistently explain the performance of dye-fullerene solar cells. The best performance (η ∼ 1.5%) was obtained for simple bilayer 6T-SQ:C60 or 18T-SQ:C60 cells without annealing. Our results demonstrate that the attachment of decorating moieties to a central light-absorbing core unit in molecular push–pull systems can be used to adjust the optoelectronic and morphological film properties of small molecular semiconductors with a strong tendency towards crystallization.

This paper reports β-lactoglobulin amyloid protein fibrils directed synthesis of Titanium Dioxide (TiO2) hybrid nanowires. Protein fibrils act as templates to generate closely packed TiO2 nanoparticles on the surface of the fibrils using titanium (IV) bis (ammonium lactato) dihydroxide (TiBALDH) as precursor, resulting in the TiO2–coated amyloid hybrid nanowires. These amyloid fibrils also exhibit complexation with a luminescent water-soluble semiconductive polythiophene (P3HT). TiO2 nanowires behave as electron acceptor while, P3HT as electron donor. In this way, amyloid-TiO2 hybrid nanowires can serve in heterojunction photovoltaic devices. To demonstrate this, a photovoltaic active layer is prepared by spin coating the blended mixture of polythiophene-coated fibrils and amyloid-TiO2 hybrid nanowires. The current–voltage characteristics of these photovoltaic devices exhibit excellent fill factor of 0.53, photovoltaic current density of 3.97 mA·cm−2 and power conversion efficiency of 0.72%, highlighting a possible future role for amyloid-based templates in donor–acceptor devices, organic electronics and hybrid solar cells.

A series of N-heterocyclic carbene-based AuI–σ-acetylide complexes of the type [(Bimz)Au–C≡CR] (Bimz = benzimidazolin-2-ylidene; R = aryl, silyl groups) (1a–1l, 2, 3) were prepared from the precursor [(Bimz)AuICl] by an in situ deprotonation of the terminal alkynes. Steady-state photoluminescence studies revealed that most of these complexes exhibit phosphorescence at room temperature and in 77 K rigidified matrices. Molecular structures were determined by single-crystal X-ray diffraction studies for complexes 1a, 1b, 1e, 1f, 1h, 1k, and 1l. Complexes 1f, 1h, and 1l revealed weak unsupported aurophilic interactions. Cyclic voltammetry studies exhibited irreversible behavior with one oxidation peak potential (Ep,a) for most cases in the region 0.7–1.4 V. Experimental and DFT studies suggest that the nature of the emission is predominantly of intraligand character 3IL(π–π*) with a slight perturbation from the metal.

We describe the self-organization of PCBM and a cyanine dye on chemically patterned surfaces during spin coating from solution. On homogeneous surfaces, a transient bilayer forms, which in a later stage decomposes into PCBM droplets in a matrix of the cyanine dye. On the patterned surface also a PCBM droplet phase develops, but the final film structure is greatly determined by contact line pinning of the PCBM domains to the substrate pattern. Three characteristic morphology regimes separated by wetting transitions were observed for different ratios between the natural domain dimensions and the underlying pattern periodicity. We demonstrate that contact line pinning can be an important means to control the film morphology in systems where films are coated from solution. This process can be exploited as a general and versatile method for patterning small semiconducting molecules into 1D and 2D photonic crystals.

Selective sub-micrometer structuring of phase-separating organic semiconductor materials has recently got into focus for providing the opportunity of further improvements in optoelectronic device applications. Here we present a 3D-time-of-flight secondary ion mass spectrometry (3D-TOF-SIMS) depth profiling investigation on spin-coated blends consisting of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and a cationic cyanine dye (1,1′-diethyl-3,3,3′,3′-tetramethylcarbocyanine iodide). TOF-SIMS provides the required lateral and depth resolution to resolve material and molecular inhomogeneities and phase separation in the blend. The data are illustrating the three-dimensional arrangement of the substances involved and confirm results of earlier studies using atomic force microscopy, UV–vis spectroscopy and x-ray photoelectron spectroscopy, and which have shown well distinguishable morphological features. The formation of this domain structure has been found to be dependent on the absolute as well as the individual film thickness, in accordance with models based on thin liquid two-layer films. Honey-comb like primary structures with micrometer dimension were found in samples containing small amounts of dye molecules in the deposition solution. In this case a thin dye deposit on PCBM was detected, which is well separated from the dye layer at the substrate. For this type of sample, we discuss an extended model of film formation based on partial depletion of dye molecules during film solidification, resulting in two individual dye layers.