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In this contribution, a nanoarchitectural approach was employed to produce a nanolayer of polyoxometalate (POM) on the surface of a glassy carbon electrode (GCE) to achieve a higher surface area with higher electrocatalytic activity toward the electrochemical hydrogen evolution reaction (HER). To accomplish this, the well-known layer-by-layer (LbL) technique was employed, which involved the alternate adsorption of the POM, Na

We report on the synthesis and structural characterizaton of the first example of a PdIV-containing polyoxopalladate(ii).

Production of hydrogen through water splitting is one of the green and the most practical solutions to cope with the energy crisis and greenhouse effect. However, oxygen evolution reaction (OER) being a sluggish step, the use of precious metal-based catalysts is the main impediment toward the viability of water splitting. In this work, amorphous copper oxide and doped binary- and ternary-metal oxides (containing CoII, NiII, and CuII) have been prepared on the surface of fluorine-doped tin oxide by a facile electrodeposition route followed by thermal treatment. The fabricated electrodes have been employed as efficient binder-free OER electrocatalysts possessing a high electrochemical surface area due to their amorphous nature. The cobalt-nickel-doped copper oxide (ternary-metal oxide)-based electrode showed promising OER activity with a high current density of 100 mA cm-2 at 1.65 V versus RHE that escalates to 313 mA cm-2 at 1.76 V in alkaline media at pH 14. The high activity of the ternary-metal oxide-based electrode was further supported by a smaller semicircle in the Nyquist plot. Furthermore, all metal-oxide-based electrodes offered high stability when tested for continuous production of oxygen for 50 h. This work highlights the synthesis of efficient and cost-effective amorphous metal-based oxide catalysts to execute electrocatalytic OER employing an electrodeposition approach.

The first organofunctionalized mixed-valent polyoxo-30-molybdate wheel, [Mo

Anodes derived from SnO2 offer a greater specific capacity comparative to graphitic carbon in lithium-ion batteries (LIBs); hence, it is imperative to find a simple but effective approach for the fabrication of SnO2 . The intelligent surfacing of transition metal oxides is one of the favorite strategies to dramatically boost cycling efficiency, and currently most work is primarily aimed at coating and/or compositing with carbon-based materials. Such coating materials, however, face major challenges, including tedious processing and low capacity. This study successfully reports a new and simple WO3 coating to produce a core-shell structure on the surface of SnO2 . The empty space permitted natural expansion for the SnO2 nanostructures, retaining a higher specific capacity for over 100 cycles that did not appear in the pristine SnO2 without WO3 shell. Using WO3 -protected SnO2 nanoparticles as anode, a coin half-cell battery was designed with Li-foil as counter-electrode. Furthermore, the anode was paired with commercial LiFePO4 as cathode for a coin-type full cell and tested for lithium storage performance. The WO3 shell proved to be an effective and strong enhancer for both current rate and specific capacity of SnO2 nanoarchitectures; additionally, an enhancement of cyclic stability was achieved. The findings demonstrate that the WO3 can be used for the improvement of cyclic characteristics of other metal oxide materials as a new coating material.

We have synthesized and structurally characterized the 4-palladium(II)-containing 30-tungsto-4-arsenate(V), [Pd4(As2W15O56)2]16- (1), which represents the first palladium(II)-containing tungstoarsenate(V). The title polyanion 1 was prepared by a simple one-pot procedure in aqueous medium and characterized by single-crystal X-ray diffraction (XRD), thermogravimetric analysis (TGA), cyclic voltammetry, elemental analysis, and 183W nuclear magnetic resonance (NMR), infrared (IR), and ultraviolet-visible (UV-vis) spectroscopies. Polyanion 1 consists of four Pd2+ ions that are coordinated in a square-planar geometry to two trilacunary [As2W15O56]12- Wells-Dawson fragments resulting in a sandwich-type assembly. Catalytic studies on 1 revealed that it is an efficient catalyst precursor for the Suzuki-Miyaura cross-coupling reactions of various aryl halides in aqueous and nonaqueous media.

Reaction of the mixed-valent Mn12-acetato complex [MnIII8MnIV4O12(CH3COO)16(H2O)4] with the trilacunary Wells-Dawson-type heteropolytungstate [P2W15O56]12- in acidic acetate solution (pH 1.1) resulted in the tetra-MnIII-containing polyanion [MnIII4(H2O)2(P2W15O56)2]12- (1). Single-crystal XRD on Na12[MnIII4(H2O)2(P2W15O56)2]·84H2O (1a) revealed that four MnIII ions form a rhombic Mn4O16 core encapsulated by two [P2W15O56]12- units. X-ray photoelectron spectroscopy (XPS) data confirm the +3 oxidation state of the four manganese ions in 1. Magnetic measurements from 1.8-300 K in a 100 Oe magnetic field allowed for the extraction of full fitting parameters from the susceptibility data for 1. The negative Ja value (Ja = -2.16 ± 0.08 K, Jb = 3.24 ± 1.73 K, g = 2.35 ± 0.040, and ρ = 0.34 ± 0.03) suggests a dominant antiferromagnetic spin exchange interaction between the four MnIII ions, with the positive Jb being an accompanying result of Ja. Electrochemical studies revealed a reversible MnIV/MnIII redox couple in 1 at the +0.80 to +1.1 V potential region with E1/2 = +0.907 V.

The short-circuit current density and energy conversion efficiency of single-junction perovskite and perovskite/perovskite tandem solar cells can be increased by photon management. In this study, optical metasurfaces were investigated as potential light trapping structures oppose to commonly used pyramidal surface textures. Herein, metal oxide-based non-resonant metasurfaces were investigated as potential light-trapping structures in perovskite solar cells. The zinc oxide nanowire-based building blocks of the metasurface can be prepared by a templated electrodeposition through a mask of resist. The phase of the incident light can be controlled by the edge length of the subwavelength large zinc oxide nanowires. An array of zinc oxide nanowires was prepared and characterized in the current study. Three-dimensional (3D) finite-difference time-domain (FDTD) optical simulations were used to compare solar cells covered with non-resonant metasurfaces with commonly used light trapping structures. As compared to the solar cells covered with zinc oxide pyramid surface texture, solar cells with the integrated non-resonant metasurfaces exhibit almost identical quantum efficiencies and short-circuit current densities. Investigations of such metasurfaces will not only improve the photon absorption in perovskite solar cells but also reveal a pathway to make high-efficiency next-generation solar cells. Detailed guidelines for the realization of non-resonant metal oxide metasurfaces will be provided.

We report on the discovery of the first two examples of cationic palladium(II)-oxo clusters (POCs) containing f-metal ions, [Pd

Polymer-fullerene blends based on poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric-acid methyl ester (PCBM) have been extensively studied as promising bulk heterojunction materials for organic semiconductor devices with improved performance. In these donor–acceptor systems where the bulk morphology plays a crucial role, the generation and subsequent decay mechanisms of photoexcitation species are still not completely understood. In this work, we use femtosecond transient absorption spectroscopy to investigate P3HT:PCBM diodes under the influence of applied static electric fields in comparison to P3HT:PCBM thin films. At the same time, we try to present a detailed overview about work already done on these donor–acceptor systems. The excited state dynamics obtained at 638 nm from P3HT:PCBM thin films are found to be similar to those observed earlier in neat P3HT films, while those obtained in the P3HT:PCBM devices are affected by field-induced exciton dissociation, resulting not only in comparatively slower decay dynamics, but also in bimolecular deactivation processes. External electric fields are expected to enhance charge generation in the investigated P3HT:PCBM devices by dissociating excitons and loosely bound intermediate species like polaron pairs (PPs) and charge transfer (CT) excitons, which can already dissociate only due to the intrinsic fields at the donor–acceptor interfaces. Our results clearly establish the formation of PP-like transient species different from CT excitons in the P3HT:PCBM devices as a result of a field-induced diffusion-controlled exciton dissociation process. We find that the loosely bound transient species formed in this way also are reduced in part via a bimolecular annihilation process resulting in charge loss in typical donor–acceptor P3HT:PCBM bulk heterojunction semiconductor devices, which is a rather interesting finding important for a better understanding of the performance of these devices.

The patterning of gold and silver micro and nanostructures on rigid and flexible substrates is investigated by microcontact printed thiol based self-assembled monolayers. The aspect ratio of the noble metal micro and nanostructures is determined by interaction of the -SH head group of the CH3(CH2)19SH molecules and the surface of the noble metal. Silver micro and nanostructures with >10 times higher aspect ratios can be realized in comparison to commonly realized gold micro and nanostructures. The printing process is described, and the etching process is characterized in terms of etching window and etching selectivity. Potential electronic and photonic applications of the micro and nanostructures are discussed taking the boundary conditions of the printing process and the selected material system into consideration.

The class of peroxo-cerium-containing polyoxometalates has been discovered via the synthesis of the 9-peroxo-6-cerium(IV)-containing 30-tungsto-3-germanate, [CeIV6(O2)9(GeW10O37)3]24– (1). Polyanio...

A simple wet-chemical synthesis of layered MoS2 thin films on sapphire is reported. The gap in understanding solution processed MoS2 deposition needs to be closed to exploit all its excellent properties for low-cost applications. In this work, as deposited Mo-precursor thin films were prepared based on the solubility and coating properties of Molybdenum(V) chloride in 1-Methoxy-2-propanol. Subsequent annealing of the deposited amorphous Mo-precursor films in the presence of sulfur resulted in the formation of highly crystalline layered MoS2 films on sapphire. Improved crystallinity of the deposited films was achieved by increasing the process temperature and performing the post-annealing treatment. Post-annealing at temperatures above 900 °C increased the uniformity of multilayer films, together with the increase of MoS2 grain size. For charge transport analysis, top-gate top-contact thin film transistors (TFTs) based on these solution processed MoS2 films were fabricated. Ionic liquid gating of the TFT devices exhibited n-type semiconducting behaviour with field-effect mobility as high as 12.07 cm2/Vs and Ion/off ratio ∼ 106. X-ray photoelectron spectroscopy measurements revealed that the films annealed between 900 °C and 980 °C had an average chemical composition of S/Mo ∼ 1.84. This facile liquid phase synthesis method with centimeter-scale uniformity and controllable film thickness up to 1.2 ± 0.65 nm is suitable for low-cost preparation of other transition metal dichalcogenides thin films in next-generation electronics.

Color image sensing is commonly carried out by an array of color pixels. Each of the color pixels consists of at least three sensing elements in combination with optical filters for red, green and blue. The filters are arranged side-by-side limiting the total quantum efficiency of a color pixel to 1/N, where N is the number of color channels per color pixel. Hence, in the most basic filter arrangement, just consisting of a red, green, and blue filter, the upper limit of the quantum efficiency is equal to 1/3, limiting the dynamic range and color contrast of the detected optical input signal. In order to increase the quantum efficiency and improve the image quality, an alternative sensor device is proposed, which can be realized by using current semiconductor technology. The proposed sensor uses silicon optical antennas to detect the incident light. The sensor allows for detecting the color information, with quantum efficiencies approaching unity. The design of the optical antennas is described, and optimization strategies are discussed.

Here we report on the synthesis, structure, and characterization of the first example of a polyoxopalladate (POP)-based metal-organic framework (MOF). This novel class of materials comprises discrete polyoxo-13-palladate(II) nanocubes [Pd13O8(AsO4)8H6]8– decorated by four Ba2+ ions on each of two opposite faces. These secondary building units (SBUs) are linked to each other via rigid linear organic groups, resulting in a stable 3D POP-MOF framework, which exhibits interesting sorption as well as catalytic properties.

Developing a cost-effective, efficient, and stable oxygen evolution reaction (OER) catalyst is of great importance for sustainable energy conversion and storage. In this study, we report a facile one-step fabrication of cationic surfactant-assisted Prussian blue analogues (PBAs) Mx[Fe(CN)5CH3C6H4NH2]∙yC19H34NBr abbreviated as SF[Fe-Tol-M] (where SF = N-tridecyl-3-methylpyridinium bromide and M = Mn, Co and Ni) as efficient heterogeneous OER electrocatalysts. The electrocatalysts have been characterized by Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). In the presence of cationic surfactant (SF), PBAs-based electrodes showed enhanced redox current, high surface area and robust stability compared to the recently reported PBAs. SF[Fe-Tol-Co] hybrid catalyst shows superior electrochemical OER activity with a much lower over-potential (610 mV) to attain the current density of 10 mA cm−2 with the Tafel slope value of 103 mV·dec−1 than that for SF[Fe-Tol-Ni] and SF[Fe-Tol-Mn]. Moreover, the electrochemical impedance spectroscopy (EIS) unveiled that SF[Fe-Tol-Co] exhibits smaller charge transfer resistance, which results in a faster kinetics towards OER. Furthermore, SF[Fe-Tol-Co] offered excellent stability for continues oxygen production over extended reaction time. This work provides a surface assisted facile electrode fabrication approach for developing binder-free OER electrocatalysts for efficient water oxidation.

Anodes derived from SnO

We have synthesized and structurally characterized the 4-palladium(II)-containing 30-tungsto-4-arsenate(V), [Pd

Reaction of the mixed-valent Mn

We report on the synthesis and characterization of the first polyoxo-noble-metalate-containing metal-organic framework (MOF) material, wherein the preformed MIL-101 has been impregnated with the discrete, cuboid-shaped polyoxopalladate [Pd13Se8O32]6- (Pd13Se8), leading to the composite Pd13Se8@MIL-101. This material was characterized by FTIR, TGA, elemental analysis, powder-XRD, N2 sorption (BET), SEM-EDX, and XPS. Furthermore, the Pd13Se8@MIL-101 composite was shown to be an effective, stable, and recyclable heterogeneous precatalyst for the Suzuki-Miyaura cross-coupling reaction at room temperature utilizing environmentally benign solvents, such as water and methanol.

The generation and decay mechanisms of polaron pairs in organic semiconductor-based optoelectronic devices under operational conditions are relevant for a better understanding of photophysical processes affecting the device performance, since the possible occurrence of a polaron pair introduces an intermediate step in exciton dissociation into fully separated charge carriers. The role played by static electric fields in polaron-pair dynamics is important but poorly understood or not investigated in detail. In this work, insights into the polaron-pair dynamics in neat poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films and P3HT films sandwiched between electrical contacts with an applied external static electric field are probed using femtosecond pump-probe transient absorption spectroscopy. Asymmetric contacts result in P3HT devices with application-related diode characteristics. Consistent with the electric field-induced dissociation of oppositely charged species, we show that polaron-pair dissociation into charge carriers occurs in the P3HT device more significantly with increasing reverse bias, and that this process follows an initial instantaneous polaron-pair photoabsorption quenching due to a pronounced immediate loss of primary photoexcitation species (hot excitons). Furthermore, we show that the net-electric field present in the P3HT diode (including built-in-potential at 0 V bias) results in a more complex dynamics with new findings as compared to the neat-P3HT thin film case. Indeed, besides polaron pairs directly originating from hot excitons, we experimentally observe polaron-pair formation during exciton dissociation via a field-mediated generation process, resulting in a slower contribution to the overall decay dynamics. Moreover, unlike in the external electric field-free P3HT film, bimolecular annihilation processes clearly appear as an additional loss channel when a field is applied and hence have an impact on carrier generation performance in a working device.

Surface energies described by Hansen solubility parameters (HSP) of a synthetic organophilic fluoromica (MAE), molybdenum disulfide (MoS 2 ), and graphene are used to predict their delamination properties in a cyclic olefin copolymer (COC). This prediction suggests MAE as the most appropriate filler for COC, followed by MoS 2 and graphene. Nanocomposites are prepared via solution process and have been investigated on their delamination state using X-ray-diffraction (XRD), Raman spectroscopy , transmission electron microscopy (TEM), and angle-resolved light scattering (ARS). Nanocomposites based on MAE shown morphologies close to complete delamination. Agglomerations are detected in the case of MoS 2 and graphene. For a potential barrier application, water vapor transmission rates (WVTR) are experimentally determined. In such nanocomposites, inorganic fillers increase the diffusion length of water, known as tortuous path model, which enhances the barrier properties. Highest barrier enhancements are obtained using MAE based nanocomposites reducing the WVTR down to 40% of the initial value. The prediction of delamination based on Hansen solubility parameters is found to be a very helpful tool for selecting fillers in composites.

A method to measure Hansen solubility parameters for organophilic fluoromica is developed. For this purpose, fluoromica with four different intercalated molecules (surfactants) have been dispersed in various solvents. These surfactants change the fluoromica surface energies described by Hansen solubility parameters (HSP). The three Hansen solubility parameters (dispersion, polar and hydrogen bonding) of different organophilic fluoromicas have been obtained by using gravimetric analysis. The dispersion parameters for all four organophilic fluoromicas are almost identical, with a value around 17 MPa . Whereas polar and H-bonding parameters are varying with the used surfactants. Surprisingly the polar and hydrogen bonding values for hydrophobic alkyl chain tailored surfactants are higher than those for a hydrophilic surfactant with poly(ethylene glycol) chains. The determined HSP values allow calculating the dispersibility of the organophilic fluoromica in solvents via the Flory-Huggins (F-H) parameter. These F-H parameters describes the effective difference in HSP related surface energies of particles and solvent molecules and are used to identify potential solvents for an exfoliation process. With this approach, beside known solvents such as chloroform, also new potential candidates such as trichloroethylene, and benzyl ethyl ether are identified for dispersing/exfoliating modified organophilic fluoromica. This work is accompanied by X-ray diffraction (XRD) measurements to gain knowledge about the interlayer space of the different organophilic fluoromicas.

Two dimensional layers of dichalcogenide materials have attracted a lot of interests due to their potential applications in optoelectronics and energy storage. Hence, there is a large interest in establishing cheap, scalable processes for the production of low dimensional semiconducting dichalcogenide based films. In this work, well exfoliated MoS2 dispersions were prepared through a two-step liquid phase exfoliation process with N-methyl-pyrrolidone (NMP) and Isopropanol (IPA). The quality of the obtained MoS2 flakes was characterized by transmission electron microscopy, scanning electron microscopy, UV–Vis spectroscopy and Raman spectroscopy. For charge transport analysis, bottom-gate thin film transistors (TFTs) based on exfoliated MoS2 films were fabricated via spray coating technique. Electrical characterization of the obtained TFTs showed that adding a PMMA layer on top of the semiconductor lead to considerable improvements in the electrical performance. The analysis of the electrical characteristics suggests that the additional PMMA layer improves the charge transfer between adjacent flakes. Electrical measurements on TFTs with different channel length were used to separate the impact of the contact resistance and the channel resistance on the charge transport. The TFTs output curves showed non-linear current–voltage (I-V) characteristic. The non-linear behavior was attributed to the formation of Schottky barriers at the inter-flakes connection. In this work, we show a low-cost and scalable solution-based fabrication process that could boost the application of dichalcogenides in modern nanoelectronic devices.

Molecules are known to change properties when in contact with metal surfaces. Therefore, dynamics of photoinduced molecular excitons in a semiconductor also are expected to be influenced by a metal...

A novel liquid phase synthesis of MoS 2 thin films has been achieved. Solubility of Molybdenum(V) chloride in appropriate solvent was optimized while having good coating properties essential for thin film formation. Chemical conversion of the deposited Mo-precursor films on silicon/silicon dioxide substrate to MoS 2 were obtained by annealing in presence of sulfur. This novel method allows facile upscaling process to large substrates with uniform film thickness down to 4 nm, which are of high interest for future low-cost fabrication of electronic devices. UV–Vis, Raman spectroscopy, and X-ray photoelectron spectroscopy measurements confirm the formation of MoS 2 films with a stoichiometric chemical composition of Mo/S ~ 0.47. Furthermore, X-ray diffraction and Transmission electron microscopy measurements revealed formation of polycrystalline films with random grain orientation attributed to the amorphous SiO 2 surface of the substrate. Improved crystallinity of deposited films was achieved by increasing the process temperature. Annealing at temperatures above 750 °C increased the uniformity of multilayer films, together with the increase of MoS 2 grain size to 100 nm. This simple wet-chemical synthesis approach allows upscaling, controllable film thickness and is suitable for preparation of other transition metal dichalcogenides thin films for applications in the future electronics.

A fast and compact standing wave spectrometer based on semi-transparent organic photodetectors is developed. The semi-transparent organic detectors are realized using solution-based fabrication and exhibit an overall transmittance of about 20% in the visible range of the electromagnetic spectrum. The realization of a standing wave spectrometer is achieved by combining a semi-transparent organic detector with a movable mirror controlled by a piezo micro-actuator. The operating principles of the standing wave spectrometer are demonstrated using a combined illumination from two laser sources. The advantages of standing wave sensing devices based on organic materials as well as the required material properties are presented and discussed.

A simple method to achieve tailored growth of ZnO nanorods by employing self-assembled monolayer of alkanethiol molecules on a conductive substrate is introduced. Defects or pinholes in self-assembled monolayer are used to define the nucleation sites of ZnO during electrochemical deposition. The density of ZnO nanorods is tuned by the quality of self-assembled monolayer. A corresponding growth model for the growth of ZnO on self-assembled monolayer-modified substrate is proposed. The dimensions and the nucleation density of ZnO nanorods are tailored by systematically varying the quality of self-assembled monolayer and the parameters of electrochemical deposition. Furthermore, it is shown that this method also allows for laterally patterned growth of ZnO nanorods via microcontact printing of self-assembled monolayer. Electrochemical deposition of ZnO on Au surface results in dense coverage of ZnO nanorods. Self-assembled monolayers are applied on Au to tune the density of ZnO nanorods. The pinholes in self-assembled monolayer are used to define the nucleation site of ZnO.

Metal-mesh based electrode systems are a highly conductive, versatile, and inexpensive alternative to ITO-electrodes for organic photovoltaic (OPV) cells. However, they do not offer full surface conductivity and are, therefore, usually combined with an additional conductive layer (e.g. PEDOT:PSS), which enables lateral charge-transport in the area in between the metal tracks. The sheet conductivity of this additional lateral conductive layer (LCL) needs to be carefully tuned with respect to the distance of the metal tracks to reduce short circuit current (Jsc) losses and additional series resistance due to resistive losses in the LCL material. Usually, this is done via electrical simulation or via analysis of IV-measurements of a large number of devices with different LCL sheet conductivities. Here, we present the light-biased light-beam-induced-current (LB-LBIC) measurement technique as a direct way to visualize current collection losses due to PEDOT:PSS sheet resistance in metal mesh/bus bar based OPV cells. We demonstrate that with LB-LBIC we are not only able to visualize and optimize lateral charge extraction under real-device operation conditions in OPV cells based on a high-resolution metal mesh but can measure the PEDOT:PSS sheet resistance in operating OPV devices as well.

A technique for determining the material-specific morphology of a polymer–fullerene blend is presented. This technique is applied to solution processed bulk-heterojunction organic solar cells with different weight ratios of polymer–fullerene blend using the PTB7:PCBM material system. Optical and electrical characterizations show that the light absorption increases for larger polymer (PTB7) content, while the fill factor of the fabricated solar cells is improved for larger fullerene (PCBM) content. The material-specific morphologies of polymer–fullerene bulk-heterojunctions are measured by employing AFM phase imaging. The measured AFM phase images reveal that fullerene material forms flake-like clusters which are embedded in the polymer network. The size of the flakes is increasing with larger content of fullerene material. By correlating the optical and electrical properties with the measured bulk-heterojunction morphologies, the relation between bulk-heterojunction structure and solar cell performances i...

The class of peroxo-cerium-containing polyoxometalates has been discovered via the synthesis of the 9-peroxo-6-cerium(IV)-containing 30-tungsto-3-germanate, [Ce

Free falling picoliter and sub-picoliter droplets generated by an ultrasonic atomizer are studied from a top-view perspective with a high-speed camera while falling on a heated surface. Due to the small droplet size processes are dominated by surface tension (Re = 0.5, We = 10−4, Oh = 2 × 10−2) resulting in almost perfect spherical shapes. Our presented model analyzes the droplets top-view appearance and allows the extraction of static and dynamic advancing and receding contact angles. In addition, the extracted evaporation rate allows to determine the critical heat flux (CHF) and Leidenfrost point (LFP). The evaporation regimes: nucleate boiling, transition boiling and film-boiling can be clearly defined by CHF and LFP. The presented model assumes the droplet evaporation starts with a shape corresponding to the static advancing contact angle Θa and continues to the static receding contact angle Θr with pinned contact line, i.e. with a constant visible droplet area. Afterward, it evaporates with a dynamic receding contact angle Θdr until the end of its lifetime. The initial advancing contact angle is calculated from the volume of the arriving droplet in air and the measured contact area directly after landing on the surface. The analysis yields Θa = 37.2 ± 3.3° and Θdr = 9.1 ± 1.6° for DI-water on silicon with natural oxide layer at T = 110°C. Furthermore, different complex scenarios of interactions between droplets are observed for sessile droplets formation and during the evaporation process.

A large lateral size and low dimensions are prerequisites for next generation electronics. Since the first single layer MoS2 transistor reported by Kis's group in 2011, layered transition metal dichalcogenides (TMDs) have been demonstrated to be the ideal candidate for next generation electronics. However, the development of large scale and low cost growth techniques is a crucial step towards TMDs’ inclusion in modern electronics and photoelectronics. In this work we develop a cheap, wet chemical, and environment friendly deposition process for two dimensional MoS2 flakes with extended size. For our deposition process, ammonium tetrathiomolybdate (ATTM) dissolved in deionized water was used as precursor solution and was deposited on a SiO2/Si substrate through a Langmuir–Blodgett like deposition process. To our knowledge, this is the first time MoS2 flakes have been grown in an aqueous solution. Large-sized MoS2 flakes exceeding 150 μm in lateral size were obtained after thermal decomposition. Thicknesses ranging from a monolayer to 5 monolayers were confirmed by AFM and Raman spectroscopy. Further investigations revealed that the quality of the produced flakes strongly depends on the post growth thermal treatment and its atmosphere. This simple and nontoxic deposition method is suitable for the preparation of large (hybrid) transition metal dichalcogenide nanostructures for applications in next generation electronics.

Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for future electronics. Currently, the growth of TMD large area thin films/flakes is one of the biggest challenges. A novel method for the growth of ultra-thin and large area WS2 monolayer flakes has been developed by introducing a solution-based temperature-dependent process. This two-dimensional WS2 growth process is low cost and environmentally friendly. WO3 flakes are grown at the air–liquid interface using ammonium tetrathiotungstate ((NH4)2WS4, ATTW) as WS2 precursor. The process requires a moderate activation temperature as no flakes are formed at room temperature. Successful growth of flakes was observed in an aqueous solution of the precursor at a temperature between 70 °C and 90 °C. These flakes could be transferred to any substrate by a controlled dip-coating process. Large 2D WS2 flakes with a lateral size of up to 100 μm were obtained after sulfurization. The thickness ranged from a WS2 monolayer to five monolayers, as verified by atomic force microscope. The chemical reaction mechanism behind the formation of the flakes was investigated by FTIR, Raman, UV–Vis and x-ray photoelectron spectroscopy. The initial flakes were found to be made of WO3, which were successfully converted to WS2 by a post annealing step at 500 °C–900 °C. This simple and environmentally friendly growth technique can be used to produce large WS2 flakes for next generation electronics.

Diketone passivation of defect states at the surface of solution-processed zinc oxide thin film transistors is investigated. Trifluoroacetylacetophenone is used as the basis for passivating molecules due to its easy chemical variability on the phenyl ring. Electron withdrawing or donating substituents can be introduced at the phenyl ring to vary the electron density at the ketone anchoring positions of the passivating molecule. The relative change of electron density is quantified by DFT calculations for different substituents. Experimentally thin zinc oxide films are prepared by aqueous spray pyrolysis, while passivating diketones are deposited in vacuum on the ZnO surface. XPS and AFM measurements confirm the successful deposition of passivating molecules at the zinc oxide surface. Electrical characterization of passivated zinc oxide transistors is carried out for different exposure times. All diketones improve transistor stability for positive and negative bias stress. The passivated transistors show improved electrical properties with increased electron mobility and decreased disorder parameter. Finally, threshold voltages shift systematically to negative values and hysteresis clearly reduces. The experimentally determined electrical properties of passivated zinc oxide transistors show a systematic correlation to the effective electron density at the oxygen anchor atoms of diketones and higher charge results in a better performance.

A blue‐light emitting material based on a boron complex containing heteroaromatic phosphonate ligand is synthesized and characterized. The Phospho‐Fries rearrangement is used in the synthesis route of the ligand as a convenient method of introducing phosphonate groups into phenols. Structural, thermal and photophysical properties of the resulting oxazaborinin phosphonate compound have been characterized. DFT geometry optimizations were studied as well as the spatial position and symmetry of the HOMO and LUMO. Good thermal stability up to 250 °C enables vacuum deposition methods next to solution processing. Combining the work function with the optical band gap from UV‐Vis measurements shows that band alignment is possible with standard contact materials. Photoluminescence reveals an emission peak at 428 nm, which is suitable for a blue light‐emitter.

Purpose: To compare, for the first time, systematically the toxicity and phototoxicity of dyes and dye combinations used in vitreoretinal surgery. The dyes were trypan blue, brilliant blue G, trypan blue + brilliant blue G, indocyanine green, bromophenol blue, bromophenol blue + brilliant blue G, and acid violet 17, in clinically used concentrations. Methods: Human ARPE retinal pigment epithelium cells were exposed to the dyes for 30 min. For phototoxicity, the cells were exposed for 15 min to high-intensity light from a light emitting diode source with an intensity similar to surgical conditions. Toxicity was assayed either directly after exposure to either dye alone or dye and light, or with a delay of 24 h. Results: None of the dyes or their combinations was toxic when cells were exposed to them at ambient light. Acid violet led to a reduction viability by 90% already immediately after light exposure. Bromophenol blue and its combination with brilliant blue G showed strong phototoxicity (reduction of viability by 83%) when assayed with delay. Indocyanine green with different agents to adjust osmolarity (balanced salt solution, glucose, and mannitol) was not found to be toxic. Conclusion: The strong immediate phototoxicity of acid violet reflects its clinical toxicity. Bromophenol blue might also be disadvantageous for patient outcome because of its delayed phototoxicity. The other dyes (trypan blue, brilliant blue g, and indocyanine green) were not found to be toxic neither with exposure to ambient light nor after exposure to light of intensities used in surgery.

A transient current measurement technique which does not need light stimulus is developed. This illumination-free transient current (IFTC) technique offers insights on trapping states characteristics such as the capture time of the trapping states, their density of states (DOS) and the attempt-to-escape frequency of trapped carriers. For the analysis of IFTC measurements carried out on metal–insulator–semiconductor (MIS) capacitors, numerical simulation of the transient current were performed as a way around usual assumptions of short transit times which can considerably distort the values from transient current measurements. A combination of experimental data and simulations revealed the need to take into account retrapping events in order to extract the correct band tail density of states and corresponding characteristic parameters. An exponential density of states with a total density of 4 · 10 23 m−3 and a width of 50 meV was found to be representative of the band tail of spin-coated poly(3-hexlythiophene) (P3HT). A broader exponential distribution with a width of 83 meV is extracted for the interface states towards SiO2. Using a multiple trap and release model, the capturing time and the attempt-to-escape frequency of the band tail states were found to be 10 - 10 s and 10 8 s−1, respectively. With this technique, we are able to also pinpoint the energy position of the Fermi level relative to the transport energy level.

Impedance and transient current measurements on metal–insulator–semiconductor (MIS) capacitors are used as tools to thoroughly investigate the bulk and interface electronic transport properties of semiconducting polymers, i.e. poly(3-hexylthiophene) (P3HT). Distinct features were observed at both interfaces, i.e. metal–semiconductor and semiconductor–insulator. The results revealed a dispersive transport in the bulk due to the band tail of the localized states, presence of interface states at the interface between the insulator and the semiconductor and formation of a less conductive small layer at the interface semiconductor–metal contact due to intrusions of sputtered Au particles. Effects of self-assembled monolayers (SAMs) treatments of the gate insulating dielectric were investigated showing that treating the gate dielectric with either ozone or hexamethyldisilazane (HMDS) or octyltrichlorosilane (OTS) alter not only the interface semiconductor–insulator but the bulk properties as well. An exponential density of states with a width parameter of 38–58 meV depending on the surface treatment was found to be representative of the band tail of P3HT. Though both OTS and HMDS treatments slightly increase the density of interface states, only OTS treated samples showed a decrease in disorder parameter of the bulk. The latter fact can be attributed to an increase of the grain size due to a favored π-π stacking film growth. An outcome explaining the already reported increase of the lateral mobility and decrease of the vertical mobility observed upon OTS treatment of the gate insulating dielectric in poly(3-hexylthiophene) based devices.

Thin film transistors (TFT) with an indium based mixed oxide semiconductor are investigated for titanium–gold top-contacts. It is noticed that upon post annealing, in order to remove chemical residuals from top-contact lift-off steps, oxidation of titanium occurs depending on the annealing conditions. Mobility of the TFT is strongly affected by contact oxidation arising from this post lift-off annealing process. Oxidation of the top-contact is facilitated by adsorbed surface oxygen or out-diffusing oxygen from the semiconductor depending on the post lift-off annealing conditions. A passivation layer that binds effectively to surface vacancies and removes adsorbed oxygen species from the semiconductor surface is demonstrated. The combinations of this passivation layer with relatively low temperature and short post lift-off annealing in an oxygen deficient environment result in significantly reduced contact oxidation and subsequently better transistor performance. Contact resistance as low as 90 Ω cm and mobility as high as 5.3 cm 2 /V s are obtained for solution processed mixed metal oxide semiconductor in top-contact geometry.

A new method for electropolymerization of polythiophenes as anode buffer layer in combination with a PEDOT:PSS buffer in P3HT–PCBM solar cells is introduced. This approach uses a stack of PEDOT:PSS and electropolymerized polythiophene (ePT) as an anode buffer layer. A significant improvement in the short circuit current is seen in solar cells with additional thin buffer layers of ePT grown on top of PEDOT:PSS. The cells with ePT buffer layer grown with constant potential mode compared to solar cells without additional ePT buffer layer have an 18.7% increase in power conversion efficiency. However, the cells with ePT grown with cyclic potential mode result in an additional enhancement in short circuit current with a further increase of 11.7% in power conversion efficiency. This improvement is attributed to better quality of the buffer layer obtained by cyclic potential electropolymerization technique with respect to film quality and area coverage.

In this work the influence of unstructured charge-extraction/transport layers on solar cell photocurrent measurements is investigated. Photovoltaic cells incorporating unstructured conductive layers exhibit a significant amount of photoactive area spreading. This can lead to a large error in determining solar cell short circuit current density and fill factor from I - V measurements. To counteract this effect an analytical model is developed to describe the photoactive area spreading. The developed model requires only solar cell contact geometry and transport layer sheet resistance in order to calculate the spreading current from measured I - V data. Thus total removal of unwanted spreading current from experimental data and calculation of realistic solar cell efficiency is achieved. As an example this model is applied to unstructured metal mesh based organic solar cells, and presented data show that it yields more accurate results compared to the conventional shadow masking approach.

This paper outlined how to control density and shape of electrodeposited ZnO nanorods to achieve high scattering properties. Light scattering at nanostructured metal–semiconductor interfaces is a proven method to improve absorption in photovoltaic devices. Adjustment of nanostructure shape and mean distance is critical to achieve efficient light scattering. A simple model is introduced that predicts maximal suppression of the specular transmitted light, resulting in maximal light scattering. This model predicts in an ideal case, 50 % nanostructure coverage of the electrode. Furthermore, an optimal nanostructure height has been determined depending on the incident wavelength and the refractive indices. Experimentally, the crystal density on ITO substrates was adjusted by pulsing the deposition potential, thus, removing the requirement for an additional seeding layer. The solution of the diffusion equation indicated a break-to-pulse ratio of at least 2.4 for an efficient control of the crystal density during pulsed electrodeposition. In addition, the structure height was set by varying the number of pulse cycles. Such tailored ZnO nanostructures showed a suppression of the specular transmitted light beam of 83.5 % and a diffusive forward scattering efficiency of 39 % at a wavelength of 406 nm. Thus, the optical absorption of e.g. an 80-nm thick polymeric active layer of P3HT could be increased by 47 % by applying such tailored ZnO nanostructures.