On description of coulomb effects caused by doping in amorphous and disordered organic semiconductors

Several attempts were devoted recently to theoretical interpretation of the experimentally established low efficiency of chemical doping in amorphous and organic semiconductors. Some of these attempts are based on calculations of the effect of Coulomb potentials of dopant species on charge carriers in the host material. We estimate the effect of the Coulomb centres introduced by doping on the charge carriers in localized states of the host system and show that there is very strong correlation between spatial positions of dopant ions and extra charge carriers, in particular, in lightly doped materials. Previous calculations carried out in the framework of such an approach neither take the charge neutrality of the system, nor screening effects into account.