Holes columnar discotics

Hence, columnar (discotic) liquid crystals with an aromatic central core are of significant interest for application in OLEDs as an HTL, if the columnar phase can be aligned with the columns orthogonal to the substrate surface, i.e. the flow of holes from the anode to the ETL and/or emission layer is... 

As discussed in Chaps. 3 and 4, (columnar) discotic liquid crystals are oriented in columns separated by molten aliphatic chains and, consequently, they can conduct charge efficiently along the channels in one dimension. The organization of the different phases is described elsewhere [19, 20] and the efficiency of charge transport can be directly related to the short intermolecular spacing and order of different types of mesophase, with few exceptions [21]. For example, hole mobility is higher in ordered, rather than disordered, columnar phases and even higher in helically-ordered phases where molecular rotation is suppressed about the columnar axis [22], Some mesomorphic derivatives of hexabenzocoronene, for example hexaphenyl-substituted hexabenzocoronene (HBCn, see Table 8.2 for chemical structures of all discotic materials discussed here) have hole mobilities... 

Where, Ep is the average energy required to produce an electron-hole pair and P is the fraction of charge carriers that survive until the end of the pulse. The values of P are estimated according to a model that describes scavenging of the charge carriers by the aromatic cores of the columnar structures formed by the discotic molecules, see for example ref [14], Since JZftTRMc is measured in three dimensions, the intracolumnar mobility parallel to the columns JZb io is three times as big. 

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