Effect of field cycling on the ac and dc properties of Alq3 device

Abstract In this work, we have undertaken a study of the changes in the conductive properties of the ITO (Indium Tin Oxide)/Alq3 [aluminium–tris (8-hydroxyquinoline)]/Al device under successive electrical applied fields. Electrical fields up to 1.5 × 10 6 V/cm were applied and after each current–voltage measurement cycles a complete ac characterization was made. Current–voltage data reveals a space charge limited conduction trap dependent, with the exponent n in current decreasing with the successive applied electrical fields. This is accompanied by a decrease of dc resistance in the intermediate voltage region. In the high voltage region, the current–voltage curves reach to a limit. The impedance spectroscopy exhibits a Z ∗ relaxation peak with the relaxation frequency shifting towards higher values with the successively applied fields. The Cole–Cole plot shows a successively approach to a Debye relaxation. Modeling with a parallel RC circuit ( R p and C p ) in series with a resistance ( R s ), shows that the total device resistance decreases with the successive filed application while C p remains quite constant. An attempt to interpret the data considering that the field induced structural changes that re-arrange the defect density profile giving a different location of energy levels and lowering the trap energy is made.