Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
Basic Research Needs for Solar Energy Utilization - Office of ...
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thickness to 1-2 μm. Enhancing charge transport in the two phases could help overcome this<br />
problem by ensuring that electrons and holes reach the contacts be<strong>for</strong>e they recombine. Potential<br />
strategies include fabricating ordered arrays <strong>of</strong> oxide nanopillars to speed up transport toward the<br />
substrate.<br />
Potential molecular strategies to exceed the Shockley-Queisser limit include development <strong>of</strong><br />
multijunction structures as well as new light-harvesting (sensitizing) units such as selected<br />
molecular dyes and semiconductor quantum dots that can generate multiple charge carrier pairs<br />
from single high-energy photons. Multilayer and multijunction nanostructured cells can be<br />
fabricated by simple techniques such as screen printing or doctor blading. The short-circuit<br />
photocurrent output <strong>of</strong> the layers can be readily matched by changing the film thickness and<br />
effective pore size.<br />
The pursuit <strong>of</strong> high-efficiency cells should also include exploration <strong>of</strong> photon-energy upconversion<br />
schemes (e.g., using multi-band-gap nanostructures, metastable electronic states, and<br />
long-lived charge-separated molecular states). An inherent advantage <strong>of</strong> nanostructured solar<br />
cells is that all <strong>of</strong> these strategies can be implemented by manipulation <strong>of</strong> the interface rather<br />
than the bulk.<br />
POTENTIAL IMPACT<br />
Successful research on nanostructured solar cells <strong>for</strong> renewable energy is particularly relevant to<br />
the solar energy technologies programs in the United States. Since nanostructures will potentially<br />
play a prominent role in many new approaches to photovoltaic conversion, the research is<br />
directly related to the National Nanotechnology Initiative, which crosses many federal agencies.<br />
REFERENCES<br />
R.J. Ellingson, M.C. Beard, J.C. Johnson, P. Yu, O.I. Micic, A.J. Nozik, A. Shabaev, and<br />
A.L. Efros, “Highly Efficient Multiple Exciton Generation in Colloidal PbSe and PbS Quantum<br />
Dots,” Nano Lett. 5, 865 (2005).<br />
M. Grätzel, “Photoelectrochemical Cells,” Nature 414, 338 (2001).<br />
M. Grätzel, “Perspectives <strong>for</strong> Dye-sensitized Nanocrystalline <strong>Solar</strong> Cells,” Prog. Photovoltaics<br />
8, 171 (2000).<br />
A.J. Nozik, “Spectroscopy and Hot Electron Relaxation Dynamics in Semiconductor Quantum<br />
Wells and Quantum Dots,” Annu. Rev. Phys. Chem. 52, 193 (2001).<br />
A.J. Nozik, “Quantum Dot <strong>Solar</strong> Cells,” Physica E 14, 115 (2002).<br />
R.D. Schaller and V.I. Klimov, “High Efficiency Carrier Multiplication in PbSe Nanocrystals:<br />
Implications <strong>for</strong> <strong>Solar</strong> <strong>Energy</strong> Conversion,” Phys. Rev. Lett. 92, 186601 (2004).<br />
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