Unipolar Films for OFETs

This section will therefore examine several unipolar blend systems that have been employed to improve OFET mobility, to enhance processability especially with a view to printing devices, to study the links between morphology and charge transport, and finally to enable novel fabrication techniques such as gate dielectric self-assembly. We will broadly divide the section into blends based on oligothiophenes and those based on acenes since this covers a large fraction of the materials and concepts investigated to date. 

In this case, d is a fitting parameter relating to the width of the sigmoidal function, / polymer IS the mobiHty of the polymer alone, and max is the maximum achievable mobility in the blend. The latter will ideally be the intrinsic mobility of the high-mobility small molecule however, this is rarely the case. The aim is to achieve a i max that is greater than simply processing the small molecule with no polymer matrix This will also be lower than the intrinsic mobility due to the problems discussed earlier with thin-film formation of highly crystalline materials. 

The model of percolation itself is relatively straightforward and is based on the fraction of a particular phase within a particular conduction pathway. The mobility within the pathway is given by 

575 kg moP and results are shown for before the American Chemical Society.) 

This supports the theories of crystalline-crystalline blend behavior discussed in Section 8.2.1. However, it should be noted that if the polymer is too crystalliz-able, it is possible for it to crystallize first leading to film microstructures dominated by the polymer and OFET mobilities closer to that of the neat polymer than that of the acene molecule. 

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