Conducting polymers photo-doping

Hendrickx E, Zhang YD, Ferrio KB, Herlocker JA, Anderson J, Armstrong NR, et al. Photo-conductive properties of PVK-based photorefractive polymer composites doped with fluo-rinated styrene chromophores. J Mater Chem 1999 9(9) 2251-8. 

Charge-carrier mobilities in amorphous disordered organic photo-conductive polymers that include molecularly doped polymers are typically near or below 10" m V s at E 10 Vm and T 295K. a-Conjugated silicon backbone polymers under similar conditions display hole mobilities around 1 m V s [40, 41]. 

These polymers are mainly known for their conductivity, particularly when doped with suitable electron donors or acceptors. Photoconductivity is marginal, and therefore these polymers are of limited interest for the study of this phenomena. Undoped and doped polyacetylene has been studied in some detail [53-57]. Undoped ds-poly-acetylene is photoconductive in UV light [54] doping with AsFs shifts the photoresponse to the visible range, but the polymer also becomes highly dark-conductive. Under certain conditions, the ratio of photo to dark... 

Dopant inclusion by co-crystallisation and vapour phase doping during polymerization have also been investigated (140). Conductivities as high as lO S/cm have been observed, but despite the apparently unperturbed crystal quality the conductivities of the doped samples were essentially isotropic. It should be noted that TS crystals grown in air contain considerable quantities of O2, this does not seem to affect their conductivity but is capable of oxidation of the polymer chain immediately after photo-excitation of charge transfer between the polymer backbone and the 2 (141). 

Another interesting applications area for fullerenes is based on materials that can be fabricated using fullerene-doped polymers. Polyvinylcarbazole (PVK) and other selected polymers, such as poly(paraphcnylene-vinylene) (PPV) and phenylmethylpolysilane (PMPS), doped with a mixture of Cgo and C70 have been reported to exhibit exceptionally good photoconductive properties [206, 207, 208] which may lead to the development of future polymeric photoconductive materials. Small concentrations of fullerenes (e.g., by weight) lead to charge transfer of the photo-excited electrons in the polymer to the fullerenes, thereby promoting the conduction of mobile holes in the polymer [209]. Fullerene-doped polymers also have significant potential for use in applications, such as photo-diodes, photo-voltaic devices and as photo-refractive materials. 

Polymers are major materials in the nanotechnology revolution, including as conductive (photo and electronic) materials. Delocalization of electrons throughout a polymer chain or matrix is important for electronic conductance. This is often accomplished through doping, which encourages flow of electrons. 

By the mid-80s it was clear to most researchers that success on the conductivity side had taken its toll on polymer processability. Attention turned back to restoring the solubility and mechanical properties of the polymer. Polyaniline received the most attention initially. The nonconductive emeraldine base form is soluble in A-methylpyrrolidone [28] and films can be cast. Subsequent doping with a protonic acid from aqueous solution, or in situ with a photo-acid generator [45], is necessary to achieve conductivity. Polyaniline is also soluble in sulfuric acid, not the most convenient of solvents. Nevertheless it proved possible to spin fibers [46], cast films and extmde sheets of conductive polyaniline sulfate, but the laboratory experiments did not make the transition into large-scale manufacmring. 

Samples prepared in this way allow a range of morphologies from microcrystalline to amorphous to be obtained. In this review it will be possible to cover only part of the literature describing measurements on such systems. The discussion will, therefore, be limited to three topics, a) the characterization of highly disordered polymers in solution and solid phases, b) photo-currents in slightly disordered solids and c) doping of PDAs to enhance conductivity,... 

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