Charge transport in molecularly doped polymers at low dopant concentrations: simulation and experiment Original Research Article

A new computational technique has been developed to simulate charge transport in dilute, energetically random, media. The results predict that in materials containing 15–20% hopping sites, the transition from field-assisted to field-saturated drift occurs within a field range of 105–106 V/cm, lower values referring to lower degrees of energetic disorder. Experimental results are reported for N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and 5′-[4-[bis(4-methylphenyl)amino]-phenyl]-N,N,N′,N′-tetrakis (4-ethylphenyl) [1,1′:3′,1″-terphenylʹ-4,rt́-diamine (EFTP) doped in either a polycarbonate (PC) or poly(styrene) (PS). While TPD doped PS fulfills all criteria of disorder controlled hopping, a superposition of disorder and polaron effects has to be invoked for EFTP in both PC or PS, the latter resulting from coupling of the charge transfer process to a torsional mode of the dopant molecule. Criteria to separate disorder and polaron effects in experimental data are briefly outlined.