Organic and Nanotechnology Solar Cells
Organic semiconductors hold promise as building blocks for organic electronics, displays, and
very low-cost solar cells. In an organic solar cell, light creates a bound electron-hole pair, called
an exciton, which separates into an electron on one side and a hole on the other side of a material
interface within the device. One result of this different “physics” is that organic solar cells can be
about 10 times thinner than thin-film solar cells. Consequently, organic solar cells could lower
costs in four ways: low-cost constituent elements (e.g., carbon, hydrogen oxygen, nitrogen
sulfur), reduced material use, high conversion efficiency (the most critical issue for this
technology), and high-volume production techniques (e.g., high-rate deposition on roll-to-roll
plastic substrates). Research examples in organic solar cells include quantum dots (a
nanotechnology) embedded in an organic polymer, liquid-crystal (small-molecule) cells, and
small-molecule chromophore cells. Solar cell efficiencies to date are low (<3–5%).
Nanotechnology for PV is exciting because the optical and electronic properties of the materials
can be tuned by controlling particle size. They may be easy to manufacture when the
nanoparticles are produced by means of chemical solution. Some of these concepts are already
being pursued commercially. Long-term stability of these devices is another major issue to be
resolved.
Storage and Distribution Costs
We note that none of the above discussion considers the costs of storage of the energy but
instead assume a free electrical grid. The current grid can only handle at most 20% of its input
power as intermittent power; hence, if solar electricity were to be used on a very large scale, the
grid costs should also be included in the total adoption costs. In addition, for solar energy to play
a role other than a fill for another baseloaded energy source, storage and transmission must be
done on a large scale and cost-effectively. At present, the primary focus on solar electricity is on
intermittent power production, but its widespread use as a primary power source will require
equal attention to obtaining cost-effective storage and/or global distribution technologies to
provide the power to the end-user on demand as opposed to when the solar resource is locally
available to the conversion device.
REFERENCES
Much of this document is based on the recent review of PV technologies by T. Surek,
U.S. Department of Energy, National Center for Photovoltaics, “Helping to Make PV the Power
of Choice,” available at http://www.nrel.gov/ncpv, and Surek (2005).
T. Bruton, N. Mason, S. Roberts, O.N. Hartley, S. Gledhill, J. Fernandez, R. Russell, W. Warta,
S. Glunz, O. Schultz, M. Hermle, and G. Willeke, in Proc. 3rd World Conf. Photovoltaic Energy
Conversion, May 11–18, 2003, Paper No. 4PL-E1-01 (IEEE Catalog Number 03CH37497).
J.F. Geisz, J.M. Olson, and D.J. Friedman, in Proc. 19th European Photovoltaic Solar Energy
Conf., June 7–11, 2004 (to be published).