Thin films of ZnO semiconductor nanorods (ZnO-nr) of 6？μm length and thin ZnO nanoparticulate films (ZnO-np) have been prepared and modified with Q-dots CdS for comparison study. PIA (photoinduced absorption spectroscopy), a multipurpose tool in the study of dye-sensitized solar cells, is used to study a quantum-dot-modified metal-oxide nanostrucutred electrode. Q-dot CdS-sensitized ZnO-nr (1D network) sensitized photoelectrode has demonstrated best performances in both photoelectrical response (IPCE max = 92%) and broadening response into far visible comparing to ZnO-np-based CdS solar cell. Preadsorbing ZnO-nr with ZnO-np does not bring further improvement. Time constant for electron injection into ZnO-nr conduction band was relatively fast decay of 6.5？ms, similar to TiO2-coated CdS, and proves at least a well pore filling of ZnO-nr film by ultrafine CdS particles. Unidirectional electron transfer mechanistic in ZnO-nr has played a major role in these performances. 1. Introduction When used as electrodes in regenerative photoelectronchemical cells, wide bandgap nanostructured metal oxide (MO) semiconductor materials can serve as carriers of solar absorbers such as organometallic dyes [1–5] or inorganic narrow bandgap semiconductors (quantum dots: Q-dots) [6–9]. Power conversion efficiencies in the range of 8–12% in diffuse daylight have been obtained in the sensitization of highly porous TiO2 film with only a submonolayer required ruthenium complex [1, 2]. On the other hand, wide bandgap semiconductors have been sensitized by short bandgap (Q-dots) semiconductor materials CdSe/TiO2 [6], CdS/TiO2-SnO2 [9] as alternative to dye sensitization. Vogel and coworkers [7] have investigated the sensitization of nanoporous TiO2, ZnO by Q-sized CdS. Photocurrent quantum yields of up to nearly 80% and opencircuit voltages up to 1？V range were obtained. Under visiblelight irradiation, only the sensitizer is excited, and electrons transferred to their conduction band are injected to the inactivated MO semiconductor conduction band. If the valence band of the sensitizer is more cathodic than the valence band of MO, hole generated in the semiconductor remains there and cannot migrate to MO. Thus, the two charges will be separated effectively. Dye-sensitized solar cells (DSCs) based on one-dimensional (1D) ZnO nanostructures, which exhibit significantly higher electron mobility than that of both TiO2 and ZnO-np films [10], have recently been attracting increasing attention [10, 11]. In contrast with the dye-sensitized solar cells, fundamental understanding for the
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