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Polymers, Electronic Properties 657

carrier ranges because of their very long deep-trapping technological promise, although, because of the infancy
lifetimes. of this class of electronic polymers, further advances lead-
For systems in which the photogeneration occurs by ing to other innovations cannot be ruled out.
photoexcitation within a polymer, such as the charge-
transfer complexes or dye-sensitized systems, the pho-
togeneration efficiency can be controlled by a geminate SEE ALSO THE FOLLOWING ARTICLES
recombination mechanism. This type of carrier recombi-
nation in molecular systems can lead to quantum efficien- ELECTRONS IN SOLIDS • FULLERENES AND CARBON
cies for photogeneration that are substantially less than NANOTUBES • ORGANIC CHEMICAL SYSTEMS,THEORY
• PHOTOGRAPHIC PROCESSES AND MATERIALS • POLY-
unity and are strongly field dependent. This may result in
a photosensitivity limitation, depending on the particular MERS,FERROELECTRIC • POLYMERS,SYNTHESIS
system, and can be overcome to some degree by increasing
the light exposure in a machine.
For other electronic applications, the magnitudes of the BIBLIOGRAPHY
carrier mobilities are of paramount importance, since they
determine the frequency response of devices or, through Chiang, C. K., Druy, M. A., Gau, S. C., Heeger, A. J., Louis, E. J.,
MacDiarmid, A. J., Park, Y. W., and Shirakawa, H. (1978). “Synthesis
the related diffusion lengths, determine ultimate collection
of highly conducting films of derivatives of poyacetylene (CH) x ,”
efficiencies in devices such as photovoltaic cells. Pendant- J. Am. Chem. Soc. 100, 1013.
group polymers and disordered molecularly doped sys- Farges, J.-P. (1994). “Organic Conductors: Fundamentals and Applica-
tems are not likely to find applications in these areas be- tions,” Marcel Dekker, New York.
cause of their low mobilities and the probable importance Kahol, P. K., Harbeke, G., and Clark, G. C. (1992). “Conjugated Con-
ducting Polymers,” Springer-Verlag, Berlin/New York.
of geminate recombination processes.
Kroschwitz, J., ed. (1988). “Electrical and Electronic Properties of Poly-
A major commercial application of highly conductive mers: A State-of-the-Art Compendium,” Wiley, New York.
polymers, such as doped polyacetylene, has yet to be re- Nalwa, H. S. (1997). “Handbook of Organic Conductive Molecules and
alized. Potential uses that have been explored or are cur- Polymers: Vol. 1, Charge-Transfer Salts, Fullerenes and Photocon-
rently under study include experimental photovoltaic and ductors,” Vol. 1, Wiley, New York.
Okamura, S., and Ranby, B. (1994). “Photoconducting Polymers/Metal-
photoelectrochemical cells and lightweight rechargeable
Containing Polymers,” Springer-Verlag, Berlin/New York.
batteries. Organic batteries, based on reversible electro- Skotheim, T. A., and Elsenbaumer, R. L. (1997). “Handbook of Con-
chemical doping, in particular, appear to hold the most ducting Polymers,” 2nd ed., Marcel Dekker, New York.