Molybdenum oxide is used as a low-resistance anode interfacial layer in applications such as organic light emitting diodes and organic photovoltaics. However, little is known about the correlation between its stoichiometry and electronic properties, such as work function and occupied gap states. In addition, despite the fact that the knowledge of the exact oxide stoichiometry is of paramount importance, few studies have appeared in the literature discussing how this stoichiometry can be controlled to permit the desirable modification of the oxide's electronic structure. This work aims to investigate the beneficial role of hydrogenation (the incorporation of hydrogen within the oxide lattice) versus oxygen vacancy formation in tuning the electronic structure of molybdenum oxides while maintaining their high work function. A large improvement in the operational characteristics of both polymer light emitting devices and bulk heterojunction solar cells incorporating hydrogenated Mo oxides as hole injection/extraction layers was achieved as a result of favorable energy level alignment at the metal oxide/organic interface and enhanced charge transport through the formation of a large density of gap states near the Fermi level.

The present study is aimed at investigating the solid state reduction of a representative series of Keggin and Dawson polyoxometalate (POM) films in contact with a metallic (aluminum) electrode and at introducing them as highly efficient cathode interlayers in organic optoelectronics. We show that, upon reduction, up to four electrons are transferred from the metallic electrode to the POM clusters of the Keggin series dependent on addenda substitution, whereas a six electron reduction was observed in the case of the Dawson type clusters. The high degree of their reduction by Al was found to be of vital importance in obtaining effective electron transport through the cathode interface. A large improvement in the operational characteristics of organic light emitting devices and organic photovoltaics based on a wide range of different organic semiconducting materials and incorporating reduced POM/Al cathode interfaces was achieved as a result of the large decrease of the electron injection/extraction barrier, the enhanced electron transport and the reduced recombination losses in our reduced POM modified devices.

Hybrid organic-inorganic films consisted of molecular layers of a Keggin-structure polyoxometalate (POM: 12-tungstophosphoric acid, H(3)PW(12)O(40)) and 1,12-diaminododecane (DD) on 3-aminopropyl triethoxysilane (APTES)-modified silicon surface, fabricated via the layer-by-layer (LBL) self-assembly method are evaluated as molecular materials for electronic devices. The effect of the fabrication process parameters, including primarily compositions of deposition solutions, on the structural characteristics of the POM-based multilayers was studied extensively with a combination of spectroscopic methods (UV, FTIR, and XPS). Well-characterized POM-based films (both single-layers and multilayers) in a controlled and reproducible way were obtained. The conduction mechanisms in single-layered and multilayered structures were elucidated by the electrical characterization of the produced films supported by the appropriate theoretical analysis. Fowler-Nordheim (FN) tunneling and percolation mechanisms were encountered in good correlation with the structural characteristics of the films encouraging further investigation on the use of these materials in electronic and, in particular, in memory devices.

Here, we report on the dual functionality of tungsten oxide for application as an efficient electron and hole injection/transport layer in organic light‐emitting diodes (OLEDs). We demonstrate hybrid polymer light‐emitting diodes (Hy‐PLEDs), based on a polyfluorene copolymer, by inserting a very thin layer of a partially reduced tungsten oxide, WO2.5, at the polymer/Al cathode interface to serve as an electron injection and transport layer. Significantly improved current densities, luminances, and luminous efficiencies were achieved, primarily as a result of improved electron injection at the interface with Al and transport to the lowest unoccupied molecular orbital (LUMO) of the polymer, with a corresponding lowering of the device driving voltage. Using a combination of optical absorption, ultraviolet spectoscopy, X‐ray photoelectron spectroscopy, and photovoltaic open circuit voltage measurements, we demonstrate that partial reduction of the WO3 to WO2.5 results in the appearance of new gap states just below the conduction band edge in the previously forbidden gap. The new gap states are proposed to act as a reservoir of donor electrons for enhanced injection and transport to the polymer LUMO and decrease the effective cathode workfunction. Moreover, when a thin tungsten oxide film in its fully oxidized state (WO3) is inserted at the ITO anode/polymer interface, further improvement in device characteristics was achieved. Since both fully oxidized and partially reduced tungsten oxide layers can be deposited in the same chamber with well controlled morphology, this work paves the way for the facile fabrication of efficient and stable Hy‐OLEDs with excellent reproducibility.

Polyoxometalate (POM) layers have been used to realize efficient and long-term stable single-junction polymer photovoltaic devices with diverse configuration and donor:acceptor combination in the photoactive blend and polymer tandem cells through functioning as effective hole extraction layers and, also, as recombination layers in the interconnecting unit of the tandem cell. Their unique properties, such as their extremely high work function (W F ) of 6.0-6.2 eV, their high degree of crystallinity without any post annealing requirements and, especially, the position of their lowest unoccupied molecular orbital (LUMO), were used to control the characteristics of optoelectronic devices. It was found that POMs having a deep LUMO level lying below the highest occupied molecular orbital (HOMO) of the donor polymer are highly beneficial for device operation due to the interfacial p-doping of the latter. We demonstrated conventional and reverse structure single-junction cells reaching an efficiency of 7.9% in the latter case and a tandem cell with an efficiency of 9.9% using an all 2 solution processed inverted structure, where a POM layer simultaneously offers enhanced hole extraction in the sub-cells and minimal losses in the recombination unit. The specific properties of four POM materials and their role as functional layers in those different types of polymer photovoltaic devices are discussed.15% are feasible for polymer tandem solar cells with an optimized pair of absorber materials with different

Highly efficient and stable organic photovoltaic (OPV) cells are demonstrated by incorporating solution‐processed hydrogen molybdenum bronzes as anode interlayers. The bronzes are synthesized using a sol‐gel method with the critical step being the partial oxide reduction/hydrogenation using an alcohol‐based solvent. Their composition, stoichiometry, and electronic properties strongly correlate with the annealing process to which the films are subjected after spin coating. Hydrogen molybdenum bronzes with moderate degree of reduction are found to be highly advantageous when used as anode interlayers in OPVs, as they maintain a high work function similar to the fully stoichiometric metal oxide, whereas they exhibit a high density of occupied gap states, which are beneficial for charge transport. Enhanced short‐circuit current, open‐circuit voltage and, fill factor, relative to reference devices incorporating either PEDOT‐PSS or a solution processed stoichiometric molybdenum oxide, are obtained for a variety of bulk heterojunction mixtures based on different polymeric donors and fullerene acceptors. In particular, high power conversion efficiencies are obtained in devices that employed the s‐HxMoO2.75 as the hole extraction layer.

Herein we report on enhanced organic solar cell performance through the incorporation of cathode interfacial layers consisting of self-organized porphyrin nanostructures with a face-on configuration. In particular, a water/methanol-soluble porphyrin molecule, the free base meso-tetrakis(1methylpyridinium-4-yl)porphyrin chloride, is employed as a novel cathode interlayer in bulk heterojunction organic photovoltaics. It is demonstrated that the self-organization of this porphyrin compound into aggregates in which molecules adopt a face-to-face orientation parallel to the organic semiconducting substrate induces a large local interfacial electric field that results in a significant enhancement of exciton dissociation. Consequently, enhanced photocurrent and open circuit voltage were obtained resulting in overall device efficiency improvement in organic photovoltaics based on bulk heterojunction mixtures of different polymeric donors and fullerene acceptors, regardless of the specific combination of donor-acceptor employed. To highlight the impact of molecular orientation a second porphyrin compound, the Zn-metallated meso-tetrakis(1-methylpyridinium-4-yl)porphyrin chloride, was also studied and it was found that it forms aggregates with an edge-to-edge molecular configuration inducing a smaller increase in the device performance.

Superhydrophobicity on transparent fluorinated ethylene propylene films with nano-protrusion morphology by Ar+ O2 plasma etching: Study of the degradation in hydrophobicity after exposure to the environment Photoresist modifications by plasma vacuum ultraviolet radiation: The role of polymer structure and plasma chemistry J. Vac. Sci. Technol. B 28, 993 (2010); 10.1116/1.3484249Ion beam deposition of tantalum pentoxide thin film at room temperature In this work we study the utilization of molecular transition metal oxides known as polyoxometalates (POMs), in particular the Keggin structure anions of the formula PW 12 O 40 3À , as active nodes for potential switching and/or fast writing memory applications. The active molecules are being integrated in hybrid Metal-Insulator/POM molecules-Semiconductor capacitors, which serve as prototypes allowing investigation of critical performance characteristics towards the design of more sophisticated devices. The charging ability as well as the electronic structure of the molecular layer is probed by means of electrical characterization, namely, capacitance-voltage and current-voltage measurements, as well as transient capacitance measurements, C (t), under step voltage polarization. It is argued that the transient current peaks observed are manifestations of dynamic carrier exchange between the gate electrode and specific molecular levels, while the transient C (t) curves under conditions of molecular charging can supply information for the rate of change of the charge that is being trapped and de-trapped within the molecular layer. Structural characterization via surface and cross sectional scanning electron microscopy as well as atomic force microscopy, spectroscopic ellipsometry, UV and Fourier-transform IR spectroscopies, UPS, and XPS contribute to the extraction of accurate electronic structure characteristics and open the path for the design of new devices with on-demand tuning of their interfacial properties via the controlled preparation of the POM layer. V C 2014 AIP Publishing LLC.