Fast electron transport in metal organic vapor deposition grown dye-sensitized ZnO nanorod solar cells.

The electron transport in dye-sensitized solar cells with a MOCVD (metal organic vapor deposition)-grown ZnO nanorod array (ZnO-N) or a mesoporous film prepared from ZnO colloids (ZnO-C) as the working electrode was compared. The electrodes were of similar thickness (2 mum) and sensitized with zinc(II) meso-tetrakis(3-carboxyphenyl)porphyrin, while the electrolyte was I(-)/I(3)(-) in 3-methoxypropionitrile. Electron transport in the ZnO-C cells was comparable with that found for colloidal TiO(2) films (transport time approximately 10 ms) and was light intensity dependent. Electron transport in solar cells with ZnO-N electrodes was about 2 orders of magnitude faster ( approximately 30 mus). Thus, the morphology of the working ZnO electrode plays a key role for the electron transport properties.

Binding studies of molecular linkers to ZnO and MgZnO nanotip films.

Two bifunctional linkers, a rigid-rod p-ethynyl-isophthalic acid capped with a Ru(II)-polypyridyl complex and 3-mercaptopropionic acid, were covalently bound to ZnO nanotip films grown by metal-organic chemical vapor deposition (MOCVD) technology. This highly vertically aligned, crystalline form of ZnO had not been functionalized before. The binding was studied by Fourier transform (FT) IR and UV spectroscopies and probed, in the case of the Ru complex, by static and dynamic fluorescence quenching. The molecules did bind through the carboxylic acid groups, and the FT-IR attenuated total reflectance spectra are indicative of a bidentate carboxylate binding mode. Other molecules (heptanoic acid, isophthalic acid, and trimethoxy(2-phenylethyl)silane) were also bound to the ZnO nanotips. A comparison was made with epitaxial ZnO films grown by MOCVD and ZnO mesoporous films prepared from colloidal solutions to investigate the effect of the ZnO morphology. The ZnO nanotips were excellent binding substrates, particularly for the rigid-rod linker. Since ZnO films are etched at low pH (< 4), novel nanotip films made of ternary MgxZn1-xO, which is formed by alloying ZnO with MgO and is more resistant to acids, were developed. The MgxZn1-xO nanotip films were employed to use linkers with acidic groups and to study the effect of pH pretreatment of the surface on the binding.