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The compound Ni4V3O10 forms a new structure type in the tetragonal space group P4/n. The material can be produced using solid-state synthesis in a narrow temperature range, and the structure was confirmed using X-ray and neutron powder diffraction data. The phase contains occupationally disordered Ni/V in tetrahedral, square pyramidal, and octahedral sites. Bond valence and neutron/X-ray co-refinements give evidence for three vanadium oxidation states (V^3+, V^4+, V^5+), making it distinct in the Ni-V-O system and placing it in a class of only nine other oxides with transition metals exhibiting three oxidation states. With a Néel temperature of 38 K and a Curie-Weiss parameter θ = -234 K, it displays frustrated antiferromagnetism, evidenced by a broad hump in the heat capacity below T_N. The structure has a percolating distorted rock-salt-like network, leading to strong superexchange, but square pyramidal linkages frustrate magnetic ordering. The magnetic structure is assumed to be incommensurate, as simple propagation vectors can be ruled out by powder neutron diffraction.

Intermediate band photovoltaics (IBPV) attempt to significantly increase photovoltaic efficiency by absorbing more photons to produce additional photocurrent without sacrificing significant photovoltage. Through creation of a density of states within the parent semiconductor gap, a partially filled intermediate band (IB) may be used as a stepping stone to allow photons with sub-band gap energy to be absorbed and generate extractable charge carriers in a two-part absorption process. Sandwiching the IB material between selective n- and p-type contacts (or the parent semiconductor) excludes this Fermi level from the contacts, thereby theoretically preserving the full photovoltage of the parent material. This design theoretcially increases the maximum efficiency of a solar cell from 40.7 to 63.2% (assuming a large concentration factor). Substitution of V into In2S3 to form V0.25In1.75S3.00 is predicted to produce nearly ideal properties to maximize efficiency under concentrated sunlight, with a band gap of 2.1 eV, and an intermediate band 0.70 eV above the valence band. While powders of this material have been fabricated previously, we report the V x In(2–x)S3 thin films. Atomic layer deposition (ALD) is ideally suited to its fabrication as compositional doping/substitution can often be simply and reproducibly achieved with simple precursor pulse sequence control. This is in contrast to many physical deposition methods in which the source composition is fixed by the target allow for composition changes when the deposition rate of each element is nonequal. We utilize an oxygen-free process for growing In2S3 but periodically incorporate a novel vanadium precursor in place of the indium precursor to achieve continuous compositional control over V and In. The physical, optical, and electrical intermediate band properties as well as photoelectrochemical performance of the V x In(2–x)S3 films will be presented. The figure shows the absorption coefficients for VxIn(2–x)S3 films as a function of the doping level x. Figure 1

Titanium dioxide (TiO2) thin films have been utilized in a wide range of applications in optoelectronics and solar energy conversion. In particular, TiO2 has been exclusively used in photovoltaic (PV) devices and photoelectrochemical (PEC) cells owing to its ability to efficiently transport electrons and passivate photoactive materials against aqueous media. However, TiO2 exhibits optimal transport properties in the crystalline anatase phase, and thus requires a high temperature annealing step at 500 °C, which significantly limits its application in temperature sensitive substrates (e.g. PET) or active materials (e.g. organic-inorganic hybrid perovskites). Moreover, while high resistance of TiO2 films necessitates the need for ultrathin films to reduce series resistance in PV devices, the synthesis of ultrathin pinhole-free TiO2 films remains a challenge through conventional deposition methods. To address these issues, TiO2 compact layers for planar perovskite PV devices were deposited via atomic layer deposition (ALD) – a chemically diverse vapor phase deposition technique with the capability to synthesize ultrathin pinhole-free films. We have investigated the influence of low temperature atomic layer deposited (ALD) compact TiO2 layers as a function of post-treatment (i.e. O3, UV-O3, 500 °C) on the performance of planar perovskite PV cells. The performance of devices indicated variations primarily in open circuit voltage (VOC) and fill factor (FF) upon various forms of post-treatment. Changes in the VOC was mainly associated with the density of states within the bandgap of TiO2 as confirmed by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Also, low temperature post-treatment (O3 and UV-O3) resulted in reduced FF compared to the conventional high temperature annealing treatment as a consequence of decreased shunt resistance. We attribute this phenomena to the amorphous nature of the low temperature post-treated compact TiO2 layers providing channels for hole conduction. However, the devices fabricated with UV-O3 treated TiO2 compact layers resulted in a comparable overall performance compared to those fabricated with the conventional post-annealing process at 500 °C, opening possibilities for its application in temperature sensitive substrates as well as active materials.

The adsorption of n-alkanethiols onto polycrystalline thin films of palladium containing a strong (111) texture produces well-organized, self-assembled monolayers. The organization of the alkane chains in the monolayer and the nature of the bonding between the palladium and the thiol were studied by contact angle measurements, optical ellipsometry, reflection absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). The XPS data reveals that a compound palladium-sulfide interphase is present at the surface of the palladium film. The RAIR spectra, ellipsometry data, and wetting properties show that the palladium-sulfide phase is terminated with an organized, methyl-terminated monolayer of alkanethiolates. The local molecular environment of the alkane chains transitions from a conformationally disordered, liquidlike state to a mostly all-trans, crystalline-like structure with increasing chain length (n = 8-26). The intensities and dichroism of the methylene and methyl stretching modes support a model for the average orientation of an ensemble of all-trans-conformer chains with a tilt angle of approximately 14-18 degrees with respect to the surface normal and a twist angle of the CCC plane relative to the tilt plane of approximately 45 degrees. The SAMs are stable in air, although the sulfur present at the surface oxidizes in air over a period of 2-5 days at room temperature. The differences in chain organization between SAMs formed by microcontact printing and by solution deposition are also examined by RAIRS and XPS.

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