Enhanced Visible Light Conversion Efficiency Using Nanocrystalline WO3 Films

Santato, Clara; Ulmann, M.; Augustyński, Jan

doi:10.1002/1521-4095(200104)13:7<511::aid-adma511>3.0.co;2-w

Cited by 170 publications

(142 citation statements)

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“…16,18,19 Nano-WO 3 is reported to have much higher PC activity compared to bulk WO 3 photoelectrodes. 5,20 This is related to the different mechanism of charge separation and charge transport in the nanocrystalline semiconductor films, which is a subject of continuing discussion. 21 The PC activity depends on the electronic structure, which is related to crystal structure and surface morphology.…”

Section: Introductionmentioning

confidence: 99%

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

2012

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Nanostructured tungsten trioxide films were prepared by reactive dc magnetron sputtering at different working pressures P tot 5 1-4 Pa. The films were characterized by scanning electron microscopy, x-ray diffraction, Rutherford backscattering spectroscopy, Raman spectroscopy, and ultraviolet-visible spectrophotometry. The films were found to exhibit predominantly monoclinic structures and have similar band gap, E g % 2.8 eV, with a pronounced Urbach tail extending down to 2.5 eV. At low P tot , strained film structures formed, which were slightly reduced and showed polaron absorption in the near-infrared region. The photodegradation rate of stearic acid was found to correlate with the stoichiometry and polaron absorption. This is explained by a recombination mechanism, whereby photoexcited electron-hole pairs recombine with polaron states in the band gap. The quantum yield decreased by 50% for photon energies close to E g due to photoexcitations to band gap states lying below the O 2 affinity level.

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Section: Introductionmentioning

confidence: 99%

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

2012

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“…Because most of these impurities are not usually isovalent, but are either donors or acceptors, the incorporation of a high concentration of impurities often leads to metal oxide films with high carrier concentration and recombination centers. As a result, the metal oxides with significantly reduced bandgap usually exhibit very small depletion widths and high recombination rate, and therefore, show poor photoresponse [15][16][17][18]. Recently, we proposed to overcome this problem by charge-compensated donor-acceptor co-doping, e.g., Ga and N co-incorporation in ZnO [19,20].…”

Section: Introductionmentioning

confidence: 99%

Effect of substrate temperature on the photoelectrochemical responses of Ga and N co-doped ZnO films

et al. 2010

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Ga-N co-doped ZnO thin films with reduced bandgaps were deposited on F-doped tin-oxide-coated glass by radio-frequency magnetron sputtering at different substrate temperatures in mixed N 2 and O 2 gas ambient. We found that Ga-N co-doped ZnO films exhibited enhanced crystallinity when compared to undoped ZnO films grown under the same conditions. Furthermore, Ga-N co-doping ensured enhanced N-incorporation ZnO thin films as the substrate temperature is increased. As a result, Ga-N co-doped ZnO thin films exhibited much improved photoelectrochemical (PEC) response, compared to ZnO thin films. Our results therefore suggest that the passive codoping approach could be a means to improve PEC response for bandgap-reduced wide-bandgap oxides through impurity incorporation.

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“…5,6 The deposition of WO 3 •H 2 O was performed using a newly developed solvothermal method. A solution of 2 mmol WCl 6 in 70 mL ethanol was prepared in a globe box filled with dry air to avoid hydrolysis of WCl 6 by atmospheric humidity.…”

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“…2.6 eV. [5][6][7][8][9] Nanocrystalline WO 3 films prepared by sol-gel techniques possessed porous network structures consisting of well-crystallized nanoparticles exhibiting a large surface area for semiconductor/liquid junctions. Since porous electrodes require a thickness of several micrometers to maximize light absorption, 10,11 the increase in thickness would increase grain boundaries, at which free electrons are scattered and recombination of photogenerated electron-hole pairs occurs, resulting in retardation of electron transfer to a back-contacted conductive substrate.…”

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confidence: 99%

“…S1 in ESI), which is close to the previously reported potentials for a WO 3 electrode. [5][6][7][8] This negative shift of the onset potential suggests that direct hole transfer to methanol to form CH 2 OH radical is more efficient than to water to form hydroxyl radical. 6 Since the CH 2 OH radical exhibited the large negative redox potential, which can transfer an electron to the conduction band of WO 3, the possibility of back-electron transfer is expected to be negligible.…”

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Fabrication and photoelectrochemical property of tungsten(vi) oxide films with a flake-wall structure

2010

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Efficient visible light-induced photoelectrochemical oxidation of water was achieved using a tungsten(IV) oxide (WO 3 ) film composed of perpendicularly oriented plate-like crystallites, a flake-wall film, prepared on a transparent conductive substrate by controlling anisotropic crystal growth of tungsten oxide hydrate (WO 3 •H 2 O) followed by calcination.Water splitting using solar light is a key technology for the establishment of a low-carbon society. 1 Because of the positive Gibbs energy change in the water splitting, a direct one-step reaction may not proceed even though compensating energy is injected from outside the system, but it can be achieved by dividing into two parts: reduction of water to hydrogen and oxidation of water. Fujishima and Honda reported, for the first time, that photoirradiated titania and platinum electrodes could be used for the oxidation and reduction parts, respectively. 2 Although such a "photoelectrochemical" cell requires additional external energy as electrical or chemical bias to compensate the potential drop due to resistance of a circuit as well as overpotentials for the redox (electron transfer) reactions, the anode and cathode can be designed and their performance can be optimized separately and individually, which is the most significant merit of photoelectrochemical systems compared with particulate photocatalytic systems. Photoelectrochemical oxidation of water to evolve molecular oxygen is induced on an n-type semiconductor electrode by valence band holes generated by band-gap excitation. 3,4 Significant incident photon-to-current conversion efficiencies (IPCEs) for oxidation of water have been reported on WO 3 films, which are responsive to the blue part of visible light owing to the band gap of ca. 2.6 eV. 5-9 Nanocrystalline WO 3 films prepared by sol-gel techniques possessed porous network structures consisting of well-crystallized nanoparticles exhibiting a large surface area for semiconductor/liquid junctions. Since porous electrodes require a thickness of several micrometers to maximize light absorption, 10,11 the increase in thickness would increase grain boundaries, at which free electrons are scattered and recombination of photogenerated electron-hole pairs occurs, resulting in retardation of electron transfer to a back-contacted conductive substrate. 8,11,12 It has been reported that films composed of perpendicularly oriented crystallites showed higher photoelectrochemical performance than that of films with nanocrystalline particles. 11,13-16 For WO 3 , there have been few works focusing on the photoelectrochemical behavior of perpendicularly oriented crystalline films. 16 Herein, for the first time, WO 3 films consisting of perpendicularly oriented crystalline flakes were successfully fabricated by a wet process using anisotropic crystal growth of WO 3 •H 2 O with a layered crystal structure. Since the crystalline flakes were oriented normal to the substrate like a wall, we named this film a flake-wall film. Figure 1a shows the crystal structure of WO 3...

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Enhanced Visible Light Conversion Efficiency Using Nanocrystalline WO3 Films

Cited by 170 publications

References 2 publications

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

Effect of substrate temperature on the photoelectrochemical responses of Ga and N co-doped ZnO films

Fabrication and photoelectrochemical property of tungsten(vi) oxide films with a flake-wall structure

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Enhanced Visible Light Conversion Efficiency Using Nanocrystalline WO3 Films

Cited by 170 publications

References 2 publications

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

Structural and optical properties of visible active photocatalytic WO3 thin films prepared by reactive dc magnetron sputtering

Effect of substrate temperature on the photoelectrochemical responses of Ga and N co-doped ZnO films

Fabrication and photoelectrochemical property of tungsten(vi) oxide films with a flake-wall structure

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Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering

Structural and optical properties of visible active photocatalytic WO₃ thin films prepared by reactive dc magnetron sputtering