Controlled p doping of the hole-transport molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-di amine with tetrafluorotetracyanoquinodimethane

A study of controlled p-type doping of the hole-transport organic molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl- 4,4′-diamine (α-NPD) with tetrafluorotetracyanoquinodimethane was performed. Direct and inverse photoemission spectroscopy, contact potential difference measurements, and in situ current-voltage (I-V) measurements were used in the study. The results show that the large relaxation energy of the ionized α-NPD molecule limits the movement of the Fermi level and, ultimately, the hole injection.