Nondispersive hole transport of liquid crystalline glasses and a cross-linked network for organic electroluminescence

Abstract

Photocurrent time-of-flight experiments are used to study the transport properties of hole-conducting nematic liquid crystals. Nondispersive transients are observed and a value of $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}$ is found for the hole mobility of a chiral nematic glass at room temperature. The hole mobility of a reactive mesogen in the nematic glass phase is increased by photopolymerization of its reactive end chains to form an insoluble network. The mobility of the network shows a weak field dependence over the temperature range 295--373 K. The experimental data can be explained by hopping between the nematic cores using a Gaussian disorder model that includes spatial correlations in the carrier energy. The density-of-state distribution obtained from the model agrees with that measured spectroscopically.