Xingfu Zhou

Construction of hollow and mesoporous ZnO microsphere: a facile synthesis and sensing property.

Mesoporous and hollow structure have been attracting increasing attention for their special properties and potential applications. Here we show a facile fabrication of hollow and mesoporous ZnO microsphere via a one-step wet chemical process using polyethylene glycol (PEG, MW 200) as the solvent and soft template. The morphology and structure of the products were characterized by using scanning electron microscopy and X-ray powder diffraction techniques. Thermal analysis and Fourier transform infrared spectroscopy techniques were also performed to show the properties of the precursor and annealed product. A possible growth mechanism of hollow and mesoporous ZnO microsphere was also proposed. The Brunauer-Emmett-Teller surface area of ZnO microsphere is 28.5 m(2)g(-1) and the size of mesopores is about 10 nm. The Photoluminescence spectra of the as-synthesized ZnO hollow microspheres were also presented. The mesoporous and hollow structure enhance the gas sensitivity of ZnO microsphere, and the obtained ZnO microspheres based sensor has an excellent performance for precision detection of ethanol and acetone with low concentration.

Sn-doped TiO2 nanorod arrays and application in perovskite solar cells

Tin-doped (Sn-doped) TiO2 nanorods arrays were successfully synthesized on a TiO2 seed layer via a mild one-pot hydrothermal method. Sn-doped TiO2 nanorods with high electron mobility were assembled into a solid perovskite solar cell. The study indicated that the introduction of the Sn element led to the change of the TiO2 band gap from 3.0 to 3.04 eV. Electrochemical impedance spectroscopy showed that the resistance of the device based on Sn-doped TiO2 nanorods was lower than that of the undoped device. The PCE of the Sn-doped perovskite device achieved 6.31%, which was almost 67% higher than that of the undoped sample.

Hollow anatase TiO2 porous microspheres with V-shaped channels and exposed (101) facets: Anisotropic etching and photovoltaic properties

Owing to the excellent physical and chemical properties for potential application in multiple fields, design and synthesis of semiconductor titanium dioxide with tailor-made crystal facets and V-shaped porous sturcuctures have attracted great research interest. In this work, we prepared hollow anatase TiO2 microspheres (HTS) with exposed (101) facets and V-shaped channels via a novel anisotropic etching method. The obtained HTS microspheres are constructed by two layers, the inner layer is TiO2 nanoparticles, while the outer layer is composed of single-crystal TiO2 nanosheets with highly exposed (101) facets and V-shaped channels. The cooperative effect of hydrogen peroxide with ammonium fluoride and an anisotropic corrosion process are proposed to understand the formation mechanism. Hydrogen peroxide decomposed to form O2 bubbles, which acted as templates for the formation of TiO2 microspheres with cavities. Fluorine ions were able to promote the formation of anatase (001) facets at the beginning of the reaction and then etch the (001) facets with the reaction progress, leaving highly exposed (101) facets and V-shaped channels along the [001] direction. Due to the unique structure of anatase TiO2 (101) single crystal nanosheets and the strong light scattering effects from the V-shaped channels, the dye-sensitized solar cells (DSSCs) based on our HTS sample have a high open voltage of 0.9 V. The optimized DSSC based on our HTS sample showed an overall light-electron conversion efficiency of 7.05% with a lower dye absorption.

Mixed-phase TiO2 nanorods assembled microsphere: crystal phase control and photovoltaic application

Here, mixed-phase TiO2 nanorods assembled microspheres were fabricated via a facile one-step hydrothermal process. The synthesized samples were investigated employing X-ray powder diffraction (XRD), Raman spectrometry, field emission-scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM). The study shows the interesting symbiotic phenomenon occurred in the mixed anatase and rutile phase TiO2. The mixed crystalline phase of anatase–rutile ratios were accurately tuned by adjusting the concentration of disodium edetate (EDTA). The crystalline phase has a great influence on their photovoltaic performance. The photoelectric conversion efficiency increases by 162% when the anatase weight ratio increases from 6% to 51%. While a 263% increase in the photoelectric conversion efficiency of the optimized mixed-phase TiO2 nanorods is achieved when compared to the pure rutile phase TiO2. Accordingly, the DSSCs based on the optimized mixed-phase TiO2 nanorods assembled microspheres show a high open circuit voltage of 0.85 V and a conversion efficiency of 8.85% with a relative low dye adsorption of 0.99 × 10−7 mol cm−2.

Promising alkoxy-wrapped porphyrins with novel push-pull moieties for dye-sensitized solar cells†‡

Dye-sensitized solar cells (DSSCs) have been considered as very promising third generation solar cells. Porphyrins are promising candidates as highly efficient sensitizers for DSSCs because of their superior light-harvesting ability in the visible region and their mimicking of photosynthesis. This paper focuses on the structure modification of porphyrin dyes for efficient DSSCs, which was based on a rational design using density functional theory (DFT) before the experiment. We synthesized and fully characterized four porphyrin dyes, named ZLD13, ZLD14, ZLD15 and ZLD16. On one hand, we used 5-ethynylthiophene-2-carboxylic acid to replace 4-ethynylbenzoic acid as the electron-withdrawing anchoring group for the first time. Property studies indicate that the aggregation of porphyrin molecules can be sufficiently suppressed via this modification. On the other hand, 4,4′-di(2-thienyl)triphenylamine moiety, which has been proved to be a electron donor group for triarylamine dyes in our previous reports, was introduced to porphyrin dyes, and energy conversion efficiencies (η) were improved by 76% (ZLD15 vs. ZLD13). After the two modifications, the energy conversion efficiency (η) of ZLD16 is comparable with an N719-based reference cell under the same conditions. Enhancement of photovoltaic performances from ZLD13 to ZLD16 is partly due to the decreased dark current and charge recombination rate.

Improvement of photovoltaic performance of DSSCs by modifying panchromatic zinc porphyrin dyes with heterocyclic units

A series of novel panchromatic D–D–π–A porphyrin dyes have been synthesized and applied to dye-sensitized solar cells. Three porphyrin dyes named JP1, JP2 and JP3, and their photophysical and electrochemical properties and photovoltaic performance were investigated and compared with reference dye YD2-O-C8. 2-Hexylthiophene chromophores were introduced to the donor groups, which extended the π-conjugation system effectively, then broadened the range of spectral response and improved the charge separation between the donor and acceptor moieties in the excited state. Moreover, this paper used thiophene-2-carboxylic acid instead of the traditional benzoic acid as an anchor group, which can make the molecules arrange to tilted orientation when adsorbed on the TiO2 surface, and this may effectively suppress the dye aggregation and prevent charge recombination. These dyes were clearly red-shifted when compared with dye YD2-O-C8. Especially for dye JP3, its maximum absorption peak was red shifted 20 nm with respect to dye YD2-O-C8 from 645 to 665 nm, and the molar extinction coefficient (6.2 × 104 M−1 cm−1) of JP3 is double that of YD2-O-C8 (3.1 × 104 M−1 cm−1) at the Q band. Dye JP3 extended the spectral response to 750 nm. The density functional theory (DFT) calculations indicated that the electronic density of the HOMO was increased by the additional thiophene units in these dyes when compared with YD2-O-C8, and this will improve the conjugation and electron donating ability. The power conversion efficiencies of JP1, JP2 and JP3 are 5.09%, 5.62% and 6.40% respectively under AM 1.5G irradiation, which are 74.5%, 82.3% and 93.7% of the YD2-O-C8 based-device (6.83%) under the same conditions.

Improvement of dye-sensitized solar cells performance through introducing different heterocyclic groups to triarylamine dyes

This paper focuses on the structure modification of triphenylamine dyes for efficient dye-sensitized solar cells (DSSCs). Three D–D–π–A dyes (TTR1–3), with triphenylamine moiety and its derivatives as the electron donor, thiophene ring as the π-bridge, and 2-(1,1-dicyanomethylene)rhodanine (DCRD) as the electron acceptor, were synthesized and fully characterized. Nanocrystalline TiO2-based DSSCs were fabricated using these dyes to investigate the effect of different donor groups introduced into triphenylamine on their photovoltaic performances. The overall power conversion efficiency (PCE) of DSSCs based on TTR1–3 with chenodeoxycholic acid (CDCA) coadsorbant are 5.20%, 5.71% and 6.30%, respectively, compared to 6.62% achieved with N719. Introduced heterocyclic group with alkyl lain into triphenylamine decreased dye absorbed amount but significantly improved the value of the open circuit voltage (Voc) and the short-circuit photocurrent (Jsc), which result from the fact that they can effectively suppress the charge recombination and prevent aggregation between adjacent molecules on TiO2. We also researched the effect of sensitization for single dyes on their photovoltaic performances. The PCEs of DSSCs soaked for 32 h increase slightly compared to those of DSSCs soaked for 16 h, which result from the adsorption quantity on the TiO2 surface. We found that, with soaking twice in 32 h, the Jsc and Voc were both obviously improved compared with soaking once in 32 h. These results provide a new approach for enhancing the photovoltaic performances of DSSCs based on single dye.

TiO2@CdSe/CdS core–shell hollow nanospheres solar paint

TiO2@CdSe/CdS core–shell hollow nanospheres solar paint was successfully prepared via hard template and ion exchange method considering the match of their band gap. The outer layer of TiO2 shell protects CdSe and CdS from decomposition and increases their stability. The diameters of the TiO2@CdSe/CdS hollow nanospheres were uniformly around 600 nm with a shell thickness of 70 nm. The visible light absorption onset of TiO2@CdSe/CdS hollow nanospheres is around 650 nm corresponding to a bandgap of 1.8 eV, showing a red-shift when compared with TiO2/CdS. TiO2@CdSe/CdS hollow nanospheres can be directly used as solar paint. The photoanode decorated by the solar paint performs a reliable photoelectric conversion efficiency of ∼0.79% and current density of 6.6 mA cm−2.

Microsphere assembly of TiO2 with tube-in-tube nanostructures: anisotropic etching and photovoltaic enhancement

We report an anisotropic etching route to prepare rutile TiO2 microspheres with a tube-in-tube nanostructure from their rod-like precursor. The crystalline structures and morphologies of both the precursor and the final product were examined by X-ray powder diffraction (XRD), field emission-scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). We also examined the photovoltaic performances of our samples by assembling them in photoanodes in dye-sensitized solar cells (DSSCs). The TiO2 microspheres sample with the tube-in-tube nanostructure shows a 213% and 269% increase in short current and conversion efficiency compared to that of TiO2 nanorods microspheres. The most interesting result in this study is that, even under the conditions with less dye adsorption (ca. 20% less), an optimized photoanode containing our TiO2 sample showed an energy-conversion efficiency of 7.57%, higher than the value (6.50%) of the photoanode containing solely anatase TiO2 nanoparticles. We concluded that the unique micro and nanostructure helps to increase the light harvesting and, thus, improve the photovoltaic performance of DSSCs.

Catalytic outgrowth of SnO2 nanorods from ZnO–SnO2 nanoparticles microsphere core: combustion synthesis and gas-sensing properties

We report for the first time the combustion synthesis of flower-like ZnO–SnO2 composite microspheres by decomposition at temperatures of 873 K in the presence of polyethylene glycol as the surfactant. A plausible mechanism for the formation of the core-shell structured microspheres is also proposed. The as-obtained sample exhibits good sensing properties against ethanol vapour at an operating temperature of 673 K, including a rapid response and recovery and high sensitivity, which makes the product a good candidate for fabricating ethanol sensors.