The effect of deep traps on carrier hopping in disordered organic materials

An analytic model of equilibrium carrier hopping conductivity in disordered organic materials with traps is formulated. The model is based on the concept of the effective transport level. It is shown that deep traps may significantly affect the energy of the transport level especially at low temperatures. This implies rather restricted applicability of the trap-controlled hopping model, which suggests that, apart from trapping, deep localized states have no influence on charge carrier kinetics within the band of hopping sites. The calculated temperature-dependence of the mobility reveals significant deviations from the linear log mu versus 1/T-2 dependence that has been considered a universal characteristic feature of disordered organic materials. (C) 2003 Elsevier Science B.V. All rights reserved.