Liquid Crystals as HTL

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 

Polycatenar compounds, with more than one terminal chain at each end of a rod-like molecule can also exhibit columnar phases, although they possess a linear molecular structure. Three linear molecules aggregate together to form a self-assembled disc. These discs then stack up to form a fluid columnar structure. Non-dispersive charge-carrier mobility in such polycatenar compounds has also been found.  

A further potential problem associated with the practical fabrication of multilayer OLEDs with low-molar-mass calamitic and columnar liquid crystals with a charge-transport layer, especially as the HTL, is the fluid nature of the liquid crystalline state. This could permit contamination of the columnar liquid crystal during the deposition of subsequent layers by the process of vapour deposition or spin-coating. The columnar materials could well be soluble in the solvent used to deposit the next layer. This would lead to chemical contamination of the individual layers due to mixing of one component into another, the 

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