Improved drive voltages of organic electroluminescent devices with an efficient p-type aromatic diamine hole-injection layer

An SbCl5-doped N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-di amine (TPD) thin film was studied as a hole-injection layer in low-molecula r-weight organic electroluminescent (EL) devices. EL characteristics of dev ices with a TPD hole-injection layer doped with other oxidizing reagents, s uch as iodine, FeCl3, and tris(4-bromophenyl)aminium hexachloroantimonate w ere compared with that of SbCl5-doped TPD. The device with SbCl5-doped TPD on a cleaned indium-tin-oxide (ITO) substrate exhibited the best performanc e of all the devices studied. The improvement in device performance was att ributed to an increase in work function of ITO due to acid formation as a r esult of hydrolysis of SbCl5 and by thinning the tunneling barrier for hole injection due to formation of the space charge region in highly doped TPD with SbCl5. (C) 2000 American Institute of Physics. [S0003- 6951(00)03950-4 ].