Facile tailoring of the electrical transport in representative hole transport materials by molecular doping

N,N'-Diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB) and 4,4',4"-tris (N-3-methylphenyl-N-phenylamine) triphenylamine (m-MTDATA) are widely used as hole transport materials in organic optoelectronic devices. In the present article, the hole transport properties of blends of NPB and m-MTDATA compared with the pristine materials are investigated using admittance spectroscopy and considering temperature dependent current-voltage characteristics and electroluminescent characteristics. It has been found that m-MTDATA dramatically lowers the carrier mobility in the NPB matrix to a large extent by enhancing the total density of traps and results in more dispersive transport. However, by introducing NPB into m-MTDATA the hole mobility is nearly unchanged in comparison with pristine m-MTDATA film. These differences are attributed to two different charge transport mechanisms, trapping and scattering. Obtained quantitative information regarding the charge transport parameters could help to extend optimization strategies for the fabrication of new organic optoelectronic devices by enabling the facile tailoring of the charge transport process.