Femtosecond IR study of excited-state relaxation and electron-injection dynamics of Ru(dcbpy){sub 2}(NCS){sub 2} in solution and on nanocrystalline TiO{sub 2} and Al{sub 2}O{sub 3} thin films
- Emory Univ., Atlanta, GA (United States). Dept. of Chemistry
- National Renewable Energy Lab., Golden, CO (United States)
Photoelectrochemical solar cells based on dye-sensitized TiO{sub 2} films have received much attention in recent years because of their potential applications as a cost-effective alternative to silicon-based cells. The photophysics and electron injection dynamics of Ru(dcbpy){sub 2}(NCS){sub 2} [dcbpy = (4,4{prime}-dicarboxy-2,2{prime}-bipyridine)] (or Ru N3) in solution and adsorbed on nanocrystalline Al{sub 2}O{sub 3} thin films were studied by femtosecond mid-IR spectroscopy. For Ru N3 in ethanol after 400 nm excitation, the long-lived metal-to-ligand charge transfer ({sup 3}MLCT) excited state with CN stretching bands at 2040 cm{sup {minus}1} was formed in less than 100 fs. No further decay of the excited-state absorption was observed within 1 ns consistent with the previously known 59 ns lifetime. For Ru N3 absorbed on Al{sub 2}O{sub 3}, an insulating substrate, the {sup 3}MLCT state was also formed in less than 100 fs. In contrast to Ru N3 in ethanol, the excited state decayed by 50% within 1 ns via multiple exponential decay while no ground-state recovery was observed. This decay is attributed to electron transfer to surface states in the band gap of Al{sub 2}O{sub 3} nanoparticles. For Ru N3 adsorbed onto the surface of TiO{sub 2}, the transient mid-IR signal was dominated by the IR absorption of injected electrons in TiO{sub 2} in the 1700--2400 cm{sup {minus}1} region. The rise time of the IR signal can be fitted by biexponential rise functions: 50 {+-} 25 fs (>84%) and 1.7 {+-} 0.5 ps (<16%) after deconvolution of instrument response function determined in a thin silicon wafer.
- OSTI ID:
- 347512
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 16; Other Information: PBD: 22 Apr 1999
- Country of Publication:
- United States
- Language:
- English
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