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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