Browsing by Author "Wu, C.-G."

Three types of flexible dye-sensitized solar cells (DSSC) were fabricated, using as the photoanode an array of TiO2 nanotubes (TNT) or TiO 2 nanotubes filled with TiO2 nanoparticles (TNT-TNP, particle size 14 nm) or TiO2 nanotubes not only filled with nanoparticles but also coated with a layer of strontium oxide (TNT-TNP-SrO). The nanotubes were obtained by electrochemical oxidation of a Ti sheet and their lengths (0.5 μm to 18.8 μm) were controlled by varying the anodization period from 0.25 to 18 h. The DSSC using titanium nanotube arrays as the photoanode (hereafter called TNT-DSSC) showed a solar-to-electricity conversion efficiency (η) of 3.46%, when the anodization period was 12 h. When TNT-TNP was used as the anode, the efficiency of the DSSC (hereafter called TNT-TNP-DSSC) has increased to 4.56%. An efficiency of 5.39% was obtained when TNT-TNP-SrO was used as the photoanode for the DSSC (hereafter called TNT-TNP-SrO-DSSC). Our own dye, coded as CYC-B1 was used in all the cases. The morphologies of TNT and TNT-TNP were characterized by FE-SEM. XRD was used to characterize the TNT. Explanations on the photovoltaic performances of the DSSCs are substantiated by using electrochemical impedance spectra (EIS), incident photon to current conversion efficiency (IPCE) curves, and Mott-Schottky plots. © 2010 The Royal Society of Chemistry.

Dye-sensitized Solar Cell (DSC) is a new generation solar cell with promising for low cost clear renewable energy. Ruthenium complexes were the best sensitizers amongst all types of molecules used for DSC. Molecular design of ruthenium complex for high efficiency DSC is an active research area. A heteroleptic ruthenium complex, coded CYC-B6S, which incorporating an antenna carbazole moiety in the ancillary ligand was used as a typical example to demonstrate the strategy of molecular design. CYC-B6S exhibits the lower energy MLCT band centered at 548 nm with a molar absorption coefficient of 1.61 × 104 M-1 cm-1. Solution state cell based on CYC-B6S show a conversion efficiency of 9.72%. 3.5% was achieved with all-solid state device based on CYC-B6S. Flexible DSCs sensitized with CYC-B6S has an efficiency of 3.8% at TiO2 thickness as small as 6.0 μm.

Quasi-solid-state dye-sensitized solar cell (qss-DSSC) is a promising photovoltaic system, intended to solve the problem of electrolyte leakage and enhance the stability of this type of cell. The most challenging issue for thus type of cell is its relatively low power conversion efficiency (η), compared with that of its counter-part cell with a liquid electrolyte. In this study, various geometric structures of carbon, i.e., graphite, carbon nanotubes (CNT) and carbon spheres (CS) are added in an ionic liquid (IL) electrolyte to fabricate qss-DSSCs. Compare to the qss-DSSC with pristine IL electrolyte, the cells with graphite, CNT, and CS modified IL electrolyte show higher conversion efficiency. The highest photovoltaic performance of the cell with CS-modified IL electrolyte is explained on the basis of enhanced conductivity, increased diffusion coefficients of I- and I3- ions, and reduced charge transfer resistances, with reference to these parameters in the cases of pristine IL or ILs with graphite or CNT. Further comparative study is made among the performances of the qss-DSSCs using the CYC-B6S dye, reported by us previously, and the conventional N3 dye, both in the presence and absence of CS in the respective IL electrolytes. Finally, stability studies are made for these qss-DSSCs under continuous light soaking at 55 °C for 1,000 hours. All these studies demonstrate that the best performance (η = 6.16%) and stability (< 95%) are exhibited by the qss-DSSC with CS-modified IL electrolyte and CYC-B6S dye. © 2014 Elsevier Ltd.

Nanocomposite, 15-crown-5-functionalized multi-wall carbon nanotubes (denoted as MWCNT-15-C-5) were synthesized and used as an additive along with the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4) in the electrolyte of a dye-sensitized solar cell (DSSC); the pertinent quasi-solid-state DSSC showed a far superior photovoltaic performance than that of a cell with bare EMIBF4 or with MWCNT-added EMIBF 4 (MWCNT/EMIBF4). The heterocyclic structure of the crown ether, 15-C-5, provides its cavities to capture the lithium ions (Li +) in a DSSC, thereby facilitating the dissolution of Li+ and I- in the electrolyte of the cell. This further contributes to an improvement in the exchange reaction of I-/I3- in the electrolyte with EMIBF4. Consequently, the values of short-circuit current density (JSC) and power-conversion efficiency (η) of the DSSC with both EMIBF4 and MWCNT-15-C-5 in its electrolyte showed an increase from 3.23 ± 0.30 to 5.53 ± 0.38 mA cm-2 and from 1.52 ± 0.04 to 2.11 ± 0.10%, respectively, with reference to the values of a DSSC with bare EMIBF 4. Moreover, the at-rest durability of this quasi-solid-state DSSC was found to be unfailing for a period of 1200 h at 100 mW cm-2 illumination. Explanations are substantiated with Raman spectra, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HR-TEM), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). © 2011 The Royal Society of Chemistry.

(Graph Presented) The sensitive type: Two new ruthenium-based supersensitizers (CYC-B6S and CYC-B6L) in which a hole-transport moiety and a conjugated segment are connected sequentially to the bipyridine of the ancillary ligand show efficiency in dye-sensitized solar cells (DSCs) of up to 9.72%. Increasing the conversion efficiency of liquid-state DSCs by connecting a carbazole moiety to the ancillary ligand of the ruthenium-based sensitizer is demonstrated. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

In this study, the photoelectrochemical characteristics of a ruthenium photosensitizer with an alkyl bithiophene group, designated as CYC-B1, are studied. The effect of mesoporous TiO2 film thickness on the photovoltaic performance of CYC-B1 and N3 dye-sensitized solar cells was investigated. The performance of the dye-sensitized nanocrystalline TiO 2 solar cells (DSSC) fabricated using CYC-B1 dye-anchored TiO 2 photoelectrode showed a convincing enhancement in cell efficiency when the TiO2 film thickness was increased from 3 μm (eff. = 5.41%) to 6 μm (eff. = 7.1935). The efficiency of the CYC-B1 -sensitized DSSC was maximum at 6 μm of the TiO2 film thickness, reached its limiting value and remained constant up to 53 μm, although a similar trend was also observed for N3 dye-sensitized DSSC, however, the maximum efficiency achieved was only at 27 μm thickness (eff. = 6.75%). As expected, the photocurrent density generated in the DSSC modified by CYC-B1 dye is larger than that from N3 dye. The effect of guanidinium thiocyanate (GuSCN) (additive) addition to the electrolyte on the photovoltaic performance of DSSCs based on CYC-B1 was also investigated. Furthermore, the electrochemical impedance spectroscopy (EIS) technique and photo-transient laser method have been employed to analyze the charge transfer resistances (Rct) and the lifetime of the injected electrons on the TiO2 containing different thicknesses. © 2008 Elsevier B.V. All rights reserved.