Hole transport in molecularly doped naphthyl diamine

The effects of dopants on the hole-transporting properties of NPB, i.e., (⁠$N,N′$-diphenyl-$N,N′$-bis(1-naphthyl)(⁠$1,1′$-biphenyl)-$4,4′$ diamine), were studied by time-of-flight technique and admittance spectroscopy. Three dopants were chosen in this study. They were 4-dicyanmethylene-2-methyl-6-4H-pyran (DCM1), rubrene (RB), and tris-(8-hydroxyquinoline) aluminum $(Alq3)$⁠. It can be shown that DCM1 behaves as hole traps whereas $Alq3$ behaves as hole scatterers in NPB. Generally, both trapping and scattering lower hole mobilities in NPB. The hole mobilities decrease when DCM1 and $Alq3$ are introduced into NPB whereas the hole mobility remains nearly unchanged when RB is doped into NPB. The effect of doping on carrier dispersion is also studied.