Analysis of deep and shallow trapping of holes in anthracene

Abstract

Hole trapping in anthracene is studied by analysing space-charge limited and thermally stimulated currents against applied voltage V and temperature T. The two methods are used for thin crystals, with continuous hole injection from a copper iodide electrode. The use of the two techniques allows a quantitative determination of the characteristics of deep and shallow traps. It is shown that, even in the range where deep traps control i(V) curves, an influence of shallow traps is still noticed. Variation of the quasi-Fermi level is stated precisely as a function of V and T. For the crystals studied, in dry air, the main level of shallow traps is about 0.65 eV above the valence band, but levels between 0.75 and 0.9 eV have been obtained by thermocurrents; the total density of deep traps, which have an exponential distribution in energy, is about 10²² m^-3.