A Study on positive hole injection from electrode to liquid-crystalline semiconductor
Abstract:Although a liquid crystalline organic semiconductor is characterized by bipolar charge transport with carrier mobility, which is as high as more than 10−3cm2/Vs and independent of electric field and temperature, it has not been clarified yet how the charge carrier injection from an electrode to a liquid crystalline organic semiconductor is governed. We have studied the current-voltage characteristics of a liquid-crystalline organic semiconductor 2-(4'-Octyphenyl)-6-dodecyloxynaphthalene (8-PNP-O12) in contact with electrodes with different work functions, and have concluded that the observed current is given by thermal positive hole generation at the interface between them in the low electric field region and by the positive hole injection from electrodes to 8-PNP-O12 according the Richardson-Schottky model in the high electric field region. The temperature dependence of the observed current has revealed the formation of an electric double layer at the interface, which depresses the positive hole injection. In order to enhance the positive hole injection, we have modified an Au electrode by a self-assembled monolayer with phenylthiols, and observed dramatic increase in current density. It has been found that the positive hole injection is enhanced with aid of the HOMO levels of phenylthiols, which act as the steps for positive holes to thermally jump from the electrode to the HOMO level of 8-PNP-O12.
Document Type: Research Article
Publication date: 2006-01-01
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