Mobility intrachain

A representative example for the information extracted from a TRMC experiment is the work of Prins et al. [141] on the electron and hole dynamics on isolated chains of solution-processable poly(thienylenevinylene) (PTV) derivatives in dilute solution. The mobility of both electrons and holes as well as the kinetics of their bimolecular recombination have been monitored by a 34-GHz microwave field. It was found that at room temperature both electrons and holes have high intrachain mobilities of fi = 0.23 0.04 cm A s and = 0.38 0.02 cm / V s V The electrons become trapped at defects or impurities within 4 ps while no trapping was observed for holes. The essential results are (1) that the trap-free mobilities of electrons and holes are comparable and (2) that the intra-chain hole mobility in PTV is about three orders of magnitude larger than the macroscopic hole mobility measured in PTV devices [142]. This proves that the mobilities inferred from ToF and FET experiments are limited by inter-chain hopping, in addition to possible trapping events. It also confirms the notion that there is no reason why electron and hole mobilities should be principally different. The fact... 

Prins P, Grozema FC, Schins JM, Patil S, Scherf U, Siebbeles LDA (2006) High intrachain hole mobility on molecular wires of ladder-type poly(p-phenylenes). Phys Rev Lett 96 146601... 

Fig. 2.8. Intrachain mobility of solitons in the t-PA calculated using the values of the diffusion coefficient given in Fig. 2.7 and the Einstein relation given in Eq. (2.10). Labeling of the curves and the symbols are the same as in Fig. 2.7 [25],...

More recent work [221-225] has not yet resolved the puzzle. It seems, however, that the small mobilities obtained initially were influenced by trapping, and the intrinsic value should be larger. Evidence for a sublinear increase in drift velocity with electric field and a tendency toward saturation has been found [224], but at a much higher field than proposed earlier. The lower limit of the low-field mobility would be about 103 cm2/V s. But since the chain length in the PDAs investigated to date is not known, the relative influence of intrachain transport and interchain hopping in this value is uncertain. It will be some time before values to be compared to a theory of transport in a CP are available. The high electron mobilities... 

In Fig. 4 the after-pulse growth of the PR-TRMC transients due to positive ion scavenging by different Tt-bond conjugated polymers in oxygen saturated benzene is illustrated. From kinetic fits to the transients, using the known free-ion yield in benzene, the intrachain hole mobility could be determined and the values were found to vary from a low of 0.02 cm /Vs for the polythiophene to a high of 0.74 cm /Vs for the polyfluorene derivative. Mobility values in the... 

Alternative approaches to improve polymer ambient stability by increasing the ionization potential have utilized electron poor comonomers in the polymer backbone. Electron deficient six-membered rings, such as 1,2-pyrazine [37] or perfluorobenzene [38], have also been introduced into the backbone. These are able to planarize the backbone through the formahon of intrachain S-N or S-F bonding interactions. Increases in ionizahon potenhal can therefore be attributed solely to an electron-withdrawing effect. Ambient stabilities were not reported, but charge carrier mobilities were on the order of 10 cm s. 

Both coil and linear or expanded-coil conformations exist in untreated PEDOT-PSS films, whereas the linear or expanded-coil conformation becomes dominant in high-conductivity PEDOT-PSS films. This conformational change results in an increase in the intrachain and interchain charge carrier mobility, so the conductivity is enhanced. ... 

The intrachain mobility is restricted by conformational and chemical defects in the PPy chain structure. Even though PPy chains are intrinsically planar and linear, many conformational and structural defects can be formed during polymerization (Figure 8.3) [5], The defects break the planarity and linearity of the PPy chain and reduce the extent of Tr-orbital overlaps. The defects include conformational defects such as 2-2 coupling with nonregular 180° rotation of the alternating pyrrole... 

Naito and co-workers used a thienothiophene linker to improve the relatively poor PL of the polythiophene in the solid state [59]. Such linkers are well known in the design of high-mobility PTs for field effect transistors and photovoltaics (see Chapter 17). The pl value of thiophene polymer 33 is close to that for regioregular P3HT (HT-9f) in solution (27 and 33 %, respectively), but is much higher in the solid state (16 and 0.3 %, respectively), which was ascribed to intrachain disorder of this less symmetric structure. Both PL in films and EL spectra of an ITO/33/A1 device showed emission at 580 nm, although no other characteristics of device performance was reported. 

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