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Published 2011 | Supplemental Material + Published
Journal Article Open

Photoselective excited state dynamics in ZnO–Au nanocomposites and their implications in photocatalysis and dye-sensitized solar cells

Abstract

Improving the performance of photoactive solid-state devices begins with systematic studies of the metal–semiconductor nanocomposites (NCs) upon which such devices are based. Here, we report the photo-dependent excitonic mechanism and the charge migration kinetics in a colloidal ZnO–Au NC system. By using a picosecond-resolved Förster resonance energy transfer (FRET) technique, we have demonstrated that excited ZnO nanoparticles (NPs) resonantly transfer visible optical radiation to the Au NPs, and the quenching of defect-mediated visible emission depends solely on the excitation level of the semiconductor. The role of the gold layer in promoting photolytic charge transfer, the activity of which is dependent upon the degree of excitation, was probed using methylene blue (MB) reduction at the semiconductor interface. Incident photon-to-current efficiency measurements show improved charge injection from a sensitizing dye to a semiconductor electrode in the presence of gold in the visible region. Furthermore, the short-circuit current density and the energy conversion efficiency of the ZnO–Au NP based dye-sensitized solar cell (DSSC) are much higher than those of a DSSC comprised of only ZnO NP. Our results represent a new paradigm for understanding the mechanism of defect-state passivation and photolytic activity of the metal component in metal–semiconductor nanocomposite systems.

Additional Information

© 2011 Royal Society of Chemistry. Received 24th March 2011, Accepted 13th May 2011. First published on the web 09 Jun 2011. SS thanks UGC and AM thanks CSIR for fellowships. We thank DST for financial grants SR/SO/BB-15/2007 and Indo-Thailand Project DST/INT/THAI/P06/2008 and also for financial support for the Unit in Nanoscience. The authors (JD, SB, TB) would like to acknowledge partial financial support from the Centre of Excellence in Nanotechnology at the Asian Institute of Technology and the National Nanotechnology Center (NANOTEC) belonging to the National Science & Technology Development Agency (NSTDA), Thailand. We wish to thank Prof. A. K. Raychaudhuri, S. N. Bose National Centre for Basic Sciences, and Dr David J. Flannigan, California Institute of Technology, for scientific discussions in improving the manuscript.

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Published - Sarkar2011p14795Physical_Chemistry_Chemical_Physics.pdf

Supplemental Material - c1cp20892f.pdf

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