Hole mobilities in sol–gel materials

New silylated precursors with hole transporting units are prepared by modification of different active molecules (carbazole, oxadiazole and tetraphenylphenylenediamine derivatives) using sol-gel precursors. Absorption and photoluminescence spectra show that the electronic structures are not significantly modified by the functionalization. Field dependence of the hole mobility of the different sol-gel layers is measured using the time-of-flight technique. The highest hole mobility is observed for the layer having tetraphenylphenylenediamine units: 5.7 × 10—5 cm2.V—1.s—1 at a field strength of E = 5 × 105 V.cm—1. For the best carbazole compound, the mobility is found to be about twentyfold lower at the same field. Further experiments are required to test these new materials as hole transporting layers in photorefractive and electroluminescent devices. Copyright © 2000 John Wiley & Sons, Ltd.