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Nick's Project Page - RISE Summer 2007 |
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Intern: Nick Anderson, Biological Sciences, University of Washington
Mentor: Nick Strandwitz
Faculty Supervisor: Galen Stuckey
Department: Materials |
QUANTUM DOT SENSITIZED PHOTOVOLTAIC DEVICES
Current photovoltaics are manufactured through energy intensive processes and
are therefore expensive. Quantum dot sensitization of nanoscopic metal oxide
semiconductors is a promising inexpensive alternative to silicon-based
semiconductors. Quantum dots (QDs) are semiconductor nanoparticles, which
exhibit quantized electronic energy levels due to their nanoscopic size. The
size of the particle determines its optical absorption properties, thus allowing
for tunable energy levels and absorption in the visible spectrum. These
particles can then incorporated into the nano-pores of semiconducting metal
oxide films to induce photocurrents by sensitizing (via electron donation) the
metal oxides to a wider range of the spectrum. A number of different variables
were tested to create the most efficient devices utilizing this concept. Cadmium
sulfide QDs were compared with lead sulfide QDs on various metal oxides,
including TiO2, SnO2, and ZnO. Two methods were employed to sensitize the
semiconductors; the SILAR technique and attachment of pre-synthesized QDs.
Various redox electrolytes were also tested, including non-aqueous cobalt
complexes, used previously in dye-sensitized solar cells, and aqueous sodium
sulfide. These redox couples were selected because they show little photo-
corrosion towards the QDs. Sandwich-cell devices were tested with focused light
from a mercury lamp, and photocurrents and photovoltages were observed. Cadmium
sulfide on TiO2 with a 2M sodium sulfide redox electrolyte doped with elemental
sulfur and sodium hydroxide produced the most photocurrent. The cobalt complexes
do not show any dark chemistry, and therefore may be better suited as redox electrolytes for QD sensitized photovoltaic devices.
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