Tengfeng Xie

Surface photovoltage characterization of a ZnO nanowire array/CdS quantum dot heterogeneous film and its application for photovoltaic devices

ZnO nanowire (NWs) arrays coated with CdS quantum dots (QDs) were successfully fabricated with a chemical bath deposition process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD) have been utilized to characterize the samples. We have studied the processes of separation and recombination of the photo-generated charges in the visible region by surface photovoltage (SPV) and transient photovoltage (TPV) measurements. By controlling the amount of attached CdS QDs we found that the surface photovoltage characteristics change significantly. With a liquid electrolyte as the hole transport medium, the quantum dot sensitized nanowire solar cells (QDSSCs) exhibited short-circuit currents ranging from 0.8 to 2.6 mA cm(-2) and open-circuit voltages of 0.35-0.44 V when illuminated with light intensity 100 mW cm(-2). The relation between the performance of QDSSCs and their photovoltage characterization was also discussed.

Synthesis and Studies of the Visible‐Light Photocatalytic Properties of Near‐Monodisperse Bi‐Doped TiO2 Nanospheres

Near-monodisperse Bi-doped anatase TiO(2) nanospheres with almost uniform diameters in the range of 117 to 87 nm were prepared simply by introducing different amounts of bismuth nitrate pentahydrate into the reaction system and subsequent calcinations. X-ray diffraction, UV-visible diffuse reflectance spectra, and X-ray photoelectron spectroscopy confirm that the doped ions substitute some of the lattice titanium atoms, and furthermore, Bi(3+) and Bi(4+) ions coexist. All the Bi-doped TiO(2) samples show much better photocatalytic activity than pure TiO(2) in the degradation of rhodamine B (RhB) under the irradiation of visible light (lambda>420 nm), and, interestingly, it was found that the degradation mechanism is different from the conventional one, which has already been reported elsewhere. The detailed mechanism is discussed in this article.

Carrier concentration-dependent electron transfer in Cu2O/ZnO nanorod arrays and their photocatalytic performance

In this paper, we have engineered the interface electronic structure in Cu2O/ZnO nanorod arrays, via adjusting the carrier concentration of Cu2O, and applied them to photocatalysis. The photoinduced charge transfer kinetics at the interface between Cu2O and ZnO were systematically investigated. The Cu2O (pH 11.0)/ZnO nanorod arrays have the largest magnitude of interfacial electric field, and photoinduced charge carriers can be separated rapidly and efficiently, which generates the highest photocatalytic efficiency for the reduction of methylviologen. Heterojunction construction is an exciting direction to pursue for highly active photocatalysts, and also offers opportunities to investigate the relationship between the electronic structure and the photocatalytic performance.

Investigation of Photocatalytic Activities over Bi2WO6/ZnWO4 Composite under UV Light and Its Photoinduced Charge Transfer Properties

Bi(2)WO(6)/ZnWO(4) composite photocatalysts have been successfully synthesized by a facile hydrothermal process. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron microcopy (TEM), and UV-vis diffuse reflectance spectrum (DRS). The results show that Bi(2)WO(6) nanoparticles grow on the primary ZnWO(4) nanorods. The Bi(2)WO(6)/ZnWO(4) composites have better UV light photocatalytic activities compared to single ZnWO(4) nanorods. Furthermore, the photoinduced charge transfer properties of Bi(2)WO(6)/ZnWO(4) composites were investigated by means of transient photovoltage (TPV) technique in detail. The interconnected interface of Bi(2)WO(6)/ZnWO(4) composites led to the low recombination ratios of photoinduced electron-hole pairs and enhanced photocatalytic activities.

Synthesis of highly efficient C-doped TiO(2) photocatalyst and its photo-generated charge-transfer properties.

Carbon-doped anatase TiO(2) was prepared by a facile hydrothermal process without adding additional carbon source. The as-prepared sample shows highly efficient photocatalytic activity, which only requires 4min and is about 11 times higher than that of Degussa P25 TiO(2) in degradation of methyl orange (MO) dye under UV light irradiation. Moreover, a highly visible-light activity is also observed. UV-vis diffuse reflectance spectra and X-ray photoelectron spectroscopy confirm that the carbon atoms are incorporated into the interstitial positions of TiO(2) lattice and form a strong interaction with titanium atoms and extend photoresponding range to 700nm. Surface photovoltage spectra (SPS) and transient photovoltage (TPV) suggest that the presence of interstitial carbons induce several localized occupied states in the gap, enhance the separation extent and restrain the recombination of the photo-induced electron and hole carriers in TiO(2).

Synthesis and Plasmon‐Induced Charge‐Transfer Properties of Monodisperse Gold‐Doped Titania Microspheres

Monodisperse gold-doped titania microspheres have been synthesized under high concentration of a titanium precursor (9.34 mM) by introducing a trace amount of chloroauric acid (CA) into the reaction system; the size of the microspheres can be easily tuned (from approximately 587 to approximately 392 nm) by varying the amount of the CA added. The plausible formation mechanism has been discussed in detail. Chloroauric acid was found to act as the stabilizing agent to induce the formation of monodisperse colloidal spheres. Gold-doped anatase titania spheres with approximately 7 nm gold nanodots on the surface were synthesized by calcination. Interestingly, results from surface photocurrent, surface photovoltage, and transient photovoltage measurements indicate that the gold nanodots exhibit different electronic properties when the gold-doped anatase titania spheres were illuminated by different wavelengths of light: one is an electron acceptor in the UV region, while the other is an electron donor in the visible region. Furthermore, the decay time of the injected plasmon-induced electrons was found to be on the millisecond timescale and increased with increasing amounts of gold doped.

Enhancement of Gas Sensing Properties of CdS Nanowire/ZnO Nanosphere Composite Materials at Room Temperature by Visible-Light Activation

CdS nanowire/ZnO nanosphere materials (CdS/ZnO) with hierarchical structure were synthesized by a three-step solvothermal process. XRD, FESEM and TEM analysis confirmed the growth of ZnO nanospheres on the surface of CdS nanowires (NWs). The transient photovoltage (TPV) measurements revealed that the interface between CdS and ZnO can inhibit the recombination of photogenerated excess carriers and prolong the lifetime of excess carriers in CdS/ZnO materials. Moreover, the CdS/ZnO materials exhibit a dramatic improvement in optoelectronic performance and visible-light-irradiation gas sensing activity, which gave 1 order of magnitude larger than that of CdS NWs in response to formaldehyde. The enhancement of sensing properties is attributed to the interfacial transport of excess carriers.

Self-assembled 3D hierarchical clew-like Bi2WO6 microspheres: Synthesis, photo-induced charges transfer properties, and photocatalytic activities

Three-dimensional (3D) hierarchical clew-like microspheres with small size of bismuth tungstate (Bi2WO6) were successfully synthesized by a simple hydrothermal route at a proper volume ratio (1 : 1) of H2O/EG mixed solution. It has been found that ethylene glycol (EG) plays important roles in the formation of the clew-like structure. Bi2WO6 with different morphologies could be obtained by simply adjusting the volume ratio of the H2O/EG in the mixed solution. The kinetic features of photo-induced charges transfer properties of samples have been discussed by surface photovoltage spectrum (SPS) and transient photovoltage (TPV) techniques in detail. The Bi2WO6 with hierarchical clew-like structure possessed the highest efficiency of electron-hole separation and the lowest recombination rate of photo-induced charges, resulting in the highest photocatalytic activity for the degradation of Orange-II under the visible light (λ > 420 nm) illumination. The information provided here is thought to be beneficial for engineering high efficient photocatalysts.

Surface treatment with Al3+on a Ti-doped α-Fe2O3 nanorod array photoanode for efficient photoelectrochemical water splitting

In this paper, we present the fabrication of Ti-doped α-Fe2O3 and surface treatment with Al3+ for application as a photoanode in photoelectrochemical water splitting. The Ti-doped α-Fe2O3 with Al3+ treatment shows a 100 mV cathodic shift of the onset potential and a notable improvement of the photocurrent density. The samples were characterized by SEM, TEM, HRTEM, XRD, Raman, UV-vis and XPS to obtain the information after surface treatment. Based on electrochemistry and photoelectrochemistry techniques, it appears that surface treatment with Al3+ passivates the surface states and decreases the accumulation of charge at the surface of Ti–Fe2O3. The results show that Ti-doped Fe2O3 with Al3+ surface treatment can be used as an efficient photoanode for photoelectrochemical water splitting.

Photovoltaic properties of a ZnO nanorod array affected by ethanol and liquid-crystalline porphyrin

A vertically aligned array of ZnO nanorods, fabricated on conductive ITO substrate in aqueous solution, was characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), and UV-visible transmission spectroscopy. Surface photovoltage (SPV) techniques based on a lock-in amplifier and a Kelvin probe were both employed to study the photogenerated charges in the system. The effects of ethanol solvent and a liquid-crystalline porphyrin, [5-(para-dodecyloxy)phenyl-10,15,20-tri-phenyl] porphyrin (DPTPP), on the photovoltage enhancement in the ZnO nanorod array were studied via SPV comparison between different irradiation directions on the system. We demonstrate that the ethanol adsorption could induce the space charge region to expand towards the ZnO/ITO interface. In the absence of ethanol, the ZnO nanorod array with the DPTPP adsorption showed enhanced SPV with reduced attenuation rate of photogenerated charge carriers. We found that the separation of photogenerated charges could be further improved by coating the surface with DPTPP and ethanol together. Furthermore, the SPV spectra patterns of the composite system with opposite incident-light directions reveal that the DPTPP molecules adsorbed just at the surface of ZnO nanorods adopt a more monomeric alignment in contrast to the aggregative state in the DPTPP bulk.