Received October 29, 2007

Abstract:

Different-sized CdSe quantum dots have been assembled on TiO₂ films composed of particle and nanotube morphologies using a bifunctional linker molecule. Upon band-gap excitation, CdSe quantum dots inject electrons into TiO₂ nanoparticles and nanotubes, thus enabling the generation of photocurrent in a photoelectrochemical solar cell. The results presented in this study highlight two major findings: (i) ability to tune the photoelectrochemical response and photoconversion efficiency via size control of CdSe quantum dots and (ii) improvement in the photoconversion efficiency by facilitating the charge transport through TiO₂ nanotube architecture. The maximum IPCE (photon-to-charge carrier generation efficiency) obtained with 3 nm diameter CdSe nanoparticles was 35% for particulate TiO₂ and 45% for tubular TiO₂ morphology. The maximum IPCE observed at the excitonic band increases with decreasing particle size, whereas the shift in the conduction band to more negative potentials increases the driving force and favors fast electron injection. The maximum power-conversion efficiency 1% obtained with CdSe-TiO₂ nanotube film highlights the usefulness of tubular morphology in facilitating charge transport in nanostructure-based solar cells. Ways to further improve power-conversion efficiency and maximize light-harvesting capability through the construction of a rainbow solar cell are discussed.

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