Polystyrene, carrier transport

Figures 12-12 and 12-13 document that trap-free SCL-conduction can, in fact, also be observed in the case of electron transport. Data in Figure 12-12 were obtained for a single layer of polystyrene with a Cl 3-subsliluted vinylquaterphenyl chain copolymer, sandwiched between an ITO anode and a calcium cathode and given that oxidation and reduction potentials of the material majority carriers can only be electrons. Data analysis in terms of Eq. (12.5) yields an electron mobility of SxlQ- cm s . The rather low value is due to the dilution of the charge carrying moiety. The obvious reason why in this case no trap-limited SCL conduction is observed is that the CFs-quaterphenyl substituent is not susceptible to chemical oxidation.

In a recent pubHcation, Alivisatos and co-workers reported the making of hybrid nanorods-polymer solar cells and their properties [122]. These solar cells were made by spin casting of a solution of both poly(3-hexylthiophene) (hole acceptor) and CdSe nanorods (electron acceptor) onto indium tin oxide glass substrates coated with poly(ethylene dioxythiophene) doped with polystyrene sulfonic acid and aluminum as a top contact. Nanorods have been used in composites so as to improve the carrier mobiHty. Indeed, the latter can be high for some inorganic semiconductors, but it is typically extremely low for conjugated polymers [123]. The use of the nanorods suppHes an interface for the charge transfer as well as a direct path for electrical transport. Also, because of their anisotropy, self-assembly of these nanorods is observed by electron microscopy. It shows... 

Most polymers (typified by polystyrene and polyethylene) are electrically insulating and have conductivities doped with iodine to become electrically conducting (values have now been reported up to olO Scm ) represented a pivotal discovery in polymer science that ultimately resulted in the award of the Nobel Prize for Chemistry in 2000 [4]. The study of electrically conducting polymers is now well advanced and two extremes in the continuum of transport mechanisms exist. If the charge carriers are present in delocalized orbitals that form a band structure along the polymer backbone, they conduct by a delocalization mechanism. In contrast, isolated groups in a polymer can function as acceptors or donors of electrons and can permit... 

Experimental investigations into the behaviour of the enzymes a-amylase and glucoamylase bound to porous polystyrene show that their activity is raised in the presence of ultrasonic irradiation. The maximum activity increase that could be obtained using an acoustic intensity of 5 kW/m amounted to >200% [172]. Similar increases have been observed for a-chymotrypsin bound to agarose [173]. Schmidt and co-workers have suggested that this is attributable to a reduction of the thickness of the unstirred diffusion layer around the carrier bodies [172], that is to say that these observations are primarily due to increased mass transport rather than any cavitational effects. 

---