We consider Carbon Nanotube (CNTs) counter electrode as alternative material to Platinum counter electrode for dye sensitized solar cells (DSSCs). Also, CNT counter electrodes having different visible light transmittance were prepared on fluorine-doped tin oxide (FTO) glass substrates by spray coating method. Microstructural images show that there are CNT-tangled layers coated on FTO glass substrates. Using such CNT counter electrodes and screen printed TiO2 electrodes, DSSCs were assembled and its I-V characteristics have been studied and compared. Light energy conversion efficiency of DSSCs increased with decreasing in light transmittance of CNT counter electrode. Our result shows that CNT counter electrode is compatible to Pt counter electrode.
The electronic state of Y doped ZnO (YZO) was calculated using the density functional theory. In this study, the program used for the calculation on theoretical structures of ZnO and YZO was Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The detail of electronic structure was obtained by the discrete variational Xα (DV-Xα) method, which is a sort of molecular orbital full potential method. The density of state and energy levels of dopant elements was shown and discussed in association with optical properties, especially related to down-conversion effect. The down-conversion effect of YZO was experimentally investigated by preparing thin films deposited on F doped SnO2 (FTO) glass substrates by sol-gel method using the spin-coating system. A homogeneous and stable solution was prepared by dissolving acetates in the solution added diethanolamine as sol-gel stabilizer. In order to confirm a ultraviolet ray interruption and down-conversion effects, the transmission spectrum and the fluorescent spectrum of YZO films were estimated. The results obtained by experiment were compared with the calculated structure.
Upscaling the dye sensitized solar cell (DSSC) is a key issue that confronting the entry of this type cells in commercial market. Performance of large size DSSCs is always poor than small size cells because of high resistive losses associated with sheet resistance of conducting glass substrates. Here we show a simple method to reduce resistive loss, also, efficient collection of photo generated carriers through silver current collectors which are prepared on both
working electrode and counter electrode substrates by screen printing method in analogy to conventional silicon solar cells. For long-term stability, to protect corrosion and to avoid charge recombination, silver current collectors were laminated by surlyn sheet. Using these substrates, DSSCs were prepared and their I-V characteristics have been studied as a function of light intensity and compared with normal cells which don't have silver carrier collectors.
For improving solar efficiencies, down conversion of high-energy photons to visible lights is discussed. The losses due to thermalization of charge carriers generated by the absorption of high-energy photons, can largely be reduced in a solar cell if more than one electron-hole pair can be generated per incident photon. The solar cell consists of dye-sensitized anatase-based TiO2, approximately 30 nm particle size, 6 μm thickness, and 6 x 6 mm2 active area, Pt counter electrode and T3/T2 electrolyte. Down conversion phosphor LiGdF4:Eu(LGF) located on the front surface of the solar cells. And we measured the photo-current, current-voltage characteristics, and down-characteristics, and down-conversion efficiency of the down conversion system.
Photo decomposition ability of ultra-fine rutile TiO2 powder was investigated using the photo-catalytic reaction in
aqueous 1.0 mmol 4-chlorophenol (4CP) solutions with pH-controlled conditions. Its photo-catalytic characteristics were
then compared with those of commercial P-25 powder having mainly anatase phase. When 4CP was completely
decomposed by the photo-catalytic reaction, HPPLTed TiO2 powder was more effective than the P-25 powder regardless
of the crystalline structures. As the photo-catalytic reaction time increased, the decomposition of 4CP in the aqueous
solution was accompanied with much consumption of OH- ions. However, in the case of the aqueous solution at pH=4
naturally obtained by mixing of water and 4CP, the photo-catalytic reaction of the HPPLTed TiO2 powder occurred more
actively, compared with in the cases of the more acidic and caustic aqueous solutions. Therefore, it is thought that the
decomposition of non-degradable 4CP would take place well at a certain amount of OH- ion concentration in the aqueous
solution, considering to show no difference in the adsorption of 4CP on the surface of TiO2 particle with various pHs of
the solution, when the HPPLTed TiO2 powder with high surface areas more than 180 m2/g was used.
Formation behavior and photo-oxidation abilities of nanostructured TiO2 powders were investigated through a direct
crystallization from aqueous TiOCl2 solutions containing various metal-chlorides at 100°C. The obtained TiO2 powders without any additives and those added with Ni2+, Fe3+ and Nb5+ ions, which have a similar positive ionic radius to Ti4+, were mainly crystallized with rutile phase, whereas those added with Al3+ and Zr4+ ions, which have a quite different positive ionic radius, were mainly crystallized with anatase phase. On the other hand, the secondary particles in the TiO2 powder consisted of acicular and spherical primary particles corresponding to rutile and anatase phases, respectively. From these results, it seems that the positive ionic radius of the additives would affect phase formation as well as morphology of TiO2 precipitates. Among the TiO2 powders prepared, Ni-added powder, which consisted mainly of rutile phase with a small amount of anatase phase, showed excellent photocatalytic ability in decomposition of 4-chlorophenol.