TiO2, ZnO nanoparticulate(-np), and ZnO-nanorod(-nr) electrodes have been modified with FeS2 (pyrite) nanoparticles. Quantum size effect is manifested by a blue shift in both absorption and photocurrent action spectra. PIA (photoinduced absorption spectroscopy), a multipurpose tool in the study of dye-sensitized solar cells, is used to study quantum-dot modified metal oxide (MO) nanostructured electrodes. The PIA spectra showed an evidence for long-lived photoinduced charge separation. Time-resolved PIA showed that recombination between electrons and holes occurs on a millisecond timescale. Incident-photon-to-current efficiencies at 400？nm are ranged between 13% and 25%. The better solar cell performance of FeS2 on ZnO-nr over ZnO-np can be ascribed to the faster, unidirectional e-transport channels through the ZnO-nr as well as the longer electron lifetimes. The lower performances of electrodes can be explained by the presence of FeS2 phases other than the photoactive pyrite phase, as evidenced from XRD study. 1. Introduction A great effort is being exerted to obtain efficient and inexpensive organic and inorganic solar cells. The approach of using semiconductor colloids for the design of optically transparent thin semiconductor films is considered as a unique and an alternative for the amorphous silicon solar cells. Under this approach, films made from colloidal metal oxide semiconductors which have large band gap have attained much attention. This is primarily because they are quite stable. In addition, they predominantly absorb in the UV region. The usefulness of these systems for solar cell applications was made possible by a basic principle, namely, sensitization of their semiconductor surfaces into visible region either by organic dyes (dye sensitization) [1–4] or by inorganic short band gap semiconductors also called quantum dots (QDs; semiconductor sensitization) [5–8]. Power conversion efficiencies in the range of 8–12% in diffuse daylight have been obtained in the ruthenium-based dye-sensitized highly porous TiO2 film [1]. On the other hand, wide band gap semiconductors have been sensitized by quantum dots, for example, CdSe/TiO2 [4] and CdS/TiO2-SnO2 [8] as alternative to dye sensitization. Vogel and coworkers [6] have investigated the sensitization of nanoporous TiO2, ZnO, and so forth by Q-sized CdS with the photocurrent quantum yields of up to 80% and open circuit voltages up to 1？V. In contrast with the dye sensitized solar cells, fundamental understanding of factors controlling the interfacial electron transfer reactions for the
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