Study of hole concentration of 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′ diamine doped with tungsten oxide by admittance spectroscopy

The effect of tungsten oxide (WO3) incorporation into 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′ diamine (NPB) layer is investigated in NPB-tris(8-hydroxyquinoline)aluminium heterojunction organic light-emitting diodes. The admittance spectroscopy studies show that increasing the WO3 volume percentage from 0% to 16% can increase the hole concentration of the NBP layer from 1.97×1014to1.90×1017cm−3 and decrease the activation energy of the resistance of the NPB layer from 0.354to0.176eV. Thus, this incorporation reduces the Ohmic loss and increases the band bending in the NBP layer near the interface, resulting in an improved hole injection via tunneling through a narrow depletion region.