Effect of substitution on the hole mobility of bis(diarylamino)biphenyl derivatives doped in poly(styrene)

The effect of substitution on hole mobility in N,N'-bis(m-tolyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (TPD) derivatives doped in polystyrene was studied using the time-of-flight technique. Mobility data were collected as a function of electric field and temperature to yield the energetic and positional disorder parameters defined in the disorder formalism. Substituted derivatives exhibit lower mobilities than regular TPD. This decrease is influenced by the change in dipole moment upon substitution of the molecule. However, the dipolar disorder contribution is found to account only partially for the large differences in mobility.