Photoemission study of the interface between phenyl diamine and treated indium-tin-oxide

The interface formation between indium-tin-oxide (ITO) having various work functions and N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamin e (NPB) was investigated using x-ray and ultraviolet photoelectron spectros copy. Phosphoric acid and tetrabutylammonium hydroxide were used to modify the ITO work function. The energy difference between the highest occupied m olecular orbital (HOMO) position of NPB and the ITO Fermi level can be vari ed substantially by surface treatment. The work function of acid-treated IT O dramatically decreases after deposition of a thin NPB layer. We attribute this to the reaction between the NPB nitrogen and the proton of the adsorb ed dipole layer. No significant reaction was observed for NPB deposited on standard ITO. (C) 1999 American Institute of Physics. [S0003-6951(99)01336- 4].