Time-Resolved Infrared Spectroscopy of Dye Sensitized TiO2
Photovoltaic Devices.
- Todd Heimer and Edwin J. Heilweil
- Optical Technology Divison (844)
- National Institute of Standards and Technology
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- Dye sensitization has become an important method for extending the
spectral response of wide bandgap semiconductors, to increase their utilization
of the solar spectrum. One of the key parameters affecting the efficiency
of photovoltaic devices using this technology is the rate of electron transfer
from the sensitizer to the semiconductor. Time-resolved infrared spectroscopy
in the 6 micrometer region was employed to study the excited state properties
of the sensitizer [Ru(4,4'-(COOCH2CH3)2-2,2'-bipyridine)(2,2'-bipyridine)2]+2
in solution and anchored to nanostructured thin films of TiO2. For the
molecules attached to TiO2, a transient absorption appears which is attributed
to electrons injected into TiO2. This absorption appears within the instrumental
time resolution (ca. 30 ps) yielding an approximate 20 ps upper limit time
constant for electron transfer from the sensitizer excited state to TiO2.
Preliminary experiments with shorter light pulses indicate an approximate
1 ps electron injection time with a possible longer component for Ru(4,4'-(COOH2)2-2,2'-bipyridine)2(NCS)2
anchored to TiO2. For these systems, electron injection dominates the microsecond
sensitizer excited state decay, resulting in a near unit quantum yield
for interfacial electron transfer.