The-Vinh Nguyen

Effect of chelating agents on the properties of TiO2–SiO2 mixed oxide for photocatalytic water decomposition

High band-gap energy and large contribution of Ti–O–Si linkage were found on the catalyst synthesized with acetyl acetone as a chelating agent in a sol–gel process. Meanwhile, when acetic acid as a chelating agent was employed, it promoted the formation of TiO2–SiO2 mixed oxide with relatively high specific surface area and high photocurrent density. Low charge transfer resistance as well as wide space charge region in TiO2–SiO2 particles prepared with acetic acid gave rise to high photocurrent density, which might result in the superior photocatalytic water decomposition for hydrogen production.

Charge storage and transfer in dye-sensitized solar cells: a study by electrochemical impedance spectroscopy

AC impedance measurement was found as an efficient tool to elucidate the charge storage and transfer in dye-sensitized solar cells. The imaginary impedance of the apparent space charge region at the dye adsorbed TiO/sub 2//electrolyte interface was inversely dependent on the density of photoexcited electrons. For a given TiO/sub 2/ material, the thicker the thickness of the substrate, the higher the charge storage and the slower the charge transfer of the resulting DSC. Accordingly, the existence of an optimized thickness of TiO/sub 2/ substrate is inherent for the highest overall conversion efficiency of a DSC fabricated with a given TiO/sub 2/ material. The combination of the charge storage or the density of photoexcited electrons in the porous TiO/sub 2/ film and the prompt charge transfer between it and TiO/sub 2//TCO glass interface was worthwhile to note for improvement on the overall conversion efficiency of DSC.

Preparation of TiO 2 thin film using modified doctor-blade method for improvement of dye-sensitized solar cell

We have demonstrated a modified doctor-blade method using a dense TiO<inf>2</inf> paste in combination with moderate compression for preparation of TiO<inf>2</inf> thin film. Dye-sensitized solar cell (DSSC) with the working area of 0.25 cm² using that novel TiO<inf>2</inf> thin film was observed to show its superior photovoltaic performance at AM 1.5: V<inf>OC</inf> of 0.77 V, J<inf>SC</inf> of 18.2 mA/cm², FF of 0.50 and η of 7.0 %. This overall conversion efficiency was approximately 2 times as much as that of a corresponding DSSC fabricated with a conventional TiO<inf>2</inf> thin film (η of 3.7%). The modified doctor-blade method was also found to significantly improve the efficiencies of DSSCs with the working areas of 0.5, 1.0 and 5.0 cm².

Photoresponse and AC impedance characterization of electrodeposited TiO2-based nanocomposite films for dye-sensitized solar cells

The effect of calcination temperature on the photoelectrochemical properties of the electrodeposited TiO₂ and TiO₂/SiO₂ films as well as the corresponding dye-sensitized solar cells (DSSCs) was investigated in combination with photoresponse and AC impedance measurement. The thermal treatment of as-prepared electrodeposited TiO₂-based films was found to decrease the charge transfer resistances at the TiO₂-based film/FTO-coated glass and the TiO₂-based film/electrolyte interfaces. Meanwhile, such the treatment could significantly increase the charge storage in the TiO₂/SiO₂ film, which is ascribed to the increase in the bonding between TiO₂ nanoparticles as well as the enhancement of the bonding between TiO₂ and SiO₂ that effectively forms the energy barrier between the TiO₂ matrix and redox electrolyte. This barrier consequently brings about the improvement of photocurrent density of the derived TiO₂/SiO₂ film and the photovoltaic performance of corresponding DSSC.

Module construction of dye-sensitized solar cells by using chemical etching

Module construction of dye-sensitized solar cells (dsscs) by using chemical etching was found as a simple process to characterize and optimize the size of unit cell in terms of photovoltaic performance of the resulting module. This method was also a simple and promising process to enlarge dssc size and commercialize dssc module. Under high intensity irradiation, the deleterious effect of internal resistance in the unit cell of dssc module was found to become significant on the photovoltaic performance of the system. Meanwhile, high active area dssc module that is always accompanied by the low external resistance gives rise to the high photovoltaic performance of the system under low intensity illumination. Accordingly, optimization of the size of unit cell is worthwhile to note for the optimum performance of resulting dssc module under a particular illumination source.

Optimization of TiO/sub 2/ substrate for dye-sensitized solar cells

The effect of pre-thermal treatment on anatase TiO/sub 2/ with high specific surface area (ca. 334 m/sup 2//g, HK) was investigated for dye-sensitized solar cell (DSC). The optimized substrate was observed on the HK pre-calcined at 450/spl deg/C (HK-450) in terms of morphological feature, crystallinity, surface area, and photocurrent density. A DSC fabricated with HK-450 exhibited the high photovoltaic performance with significantly improved short-circuit current. This was attributed to the superior morphological features of HK-450, causing the high adsorption of dye and high photocurrent density. The optimization between the morphological feature, crystallinity, specific surface area and the photocurrent density of TiO/sub 2/ substrate was found to give rise to the improved overall conversion efficiency of DSC.