ABSTRACT
The physics of charge injection through an interface, separating a metal and an organic material or two molecular materials, strongly depends on the equilibrium dark conductivity of these materials. In narrow-band and doped semiconductors, the density of free carriers is high enough to form, at zero external electric filed, a space-charge cloud of either immobile ions or less mobile carriers next to the interface. This space charge causes the band bending and provides for the same value of the Fermi energy on both sides of the interface. This region of a low intrinsic conductivity is known as the Schottky depletion zone [1,2]. In principle, the related Schottky barrier can be established in a low-conductivity material at times longer than the Maxwell relaxation time tr = e0£/yd, where £0 is the permittivity of vacuum, s the dielectric constant, and yd the equilibrium dark conductivity. However, the latter is very low in undoped conjugated polymers and tT normally exceeds all experimentally relevant times. Therefore, the Schottky depletion zone cannot be formed at a metal-polymer interface unless the metal is in contact with a heavily doped polymer [3]. Below we consider only contacts with undoped organic materials.
