Wavelength-Dependent Ultrafast Charge Carrier Separation in the WO3/BiVO4 Coupled System

Due to its ∼2.4 eV band gap, BiVO4 is a very promising photoanode material for harvesting the blue portion of the solar light for photoelectrochemical (PEC) water splitting applications. In WO3/BiVO4 heterojunction films, the electrons photoexcited in BiVO4 are injected into WO3, overcoming the lower charge carriers' diffusion properties limiting the PEC performance of BiVO4 photoanodes. Here, we investigate by ultrafast transient absorption spectroscopy the charge carrier interactions occurring at the interface between the two oxides in heterojunction systems to directly unveil their wavelength dependence. Under selective BiVO4 excitation, a favorable electron transfer from photoexcited BiVO4 to WO3 occurs immediately after excitation and leads to an increase of the trapped holes' lifetime in BiVO4. However, a recombination channel opens when both oxides are simultaneously excited, evidenced by a shorter lifetime of trapped holes in BiVO4. PEC measurements reveal the implication of these wavelength-dependent ultrafast interactions on the performances of the WO3/BiVO4 heterojunction

Photovoltaics as an Experimental Tool for Determining Frontier Orbital Energies and Photocatalytic Activity of Thiol Protected Gold Clusters

Metal clusters are an emerging photonic material with a rapidly growing library of stable, atomically precise clusters recently reported. The growing interest in metal clusters, such as thiol-protected Au clusters, is due in part to interest in this new material for light harvesting, catalysis and electron transfer studies, and high efficiency photovoltaics (i.e., metal-cluster-sensitized solar cells (MCSSC) with long-term stability). Herein, we use cobalt redox couples as a tool to investigate the electronic properties (i.e., HOMO energy level) and the wavelength-dependent photocatalytic activities of glutathione protected gold clusters. To this purpose, we have synthesized a series of cobalt complexes with bipyridine and phenanthroline derivatives in order to study Au₁₈(SR)₁₄ and Au₂₅(SR)₁₈ sensitized solar cells. Using cobalt complex mediators as an alternative to the conventional high performance I^–/I₃^– electrolyte, long-term performance of MCSSC is achieved. Furthermore, these one-electron redox mediators conclusively demonstrate the unique optical activity of clusters, with excitation-wavelength-dependent photocatalytic activity

Room Temperature Ferromagnetism in Single-Crystalline Fe5Si3 Nanowires

We have investigated electrical and magnetic properties of single-crystalline Fe5Si3 nanowires. The nanowire ensemble shows ferromagnetic properties with a high T-c of 380 K, small coercivity, and no remanence in zero field at room temperature. Such magnetic properties of the single-crystalline nanowires should give a chance to realize not only novel nanospintronic devices but also biomedical applications. Electrical transport measurements on single Fe5Si3 nanowire device show metallic properties with low resistivity of 487 mu . Omega . cm. Fe5Si3 nanowires are the first example of single-crystalline metallic ferromagnet with a T-c higher than room temperatureclose131