Thin lithium fluoride (LiF) interlayers between the low work function elect
rode and the electron transport layer in organic light emitting diodes (OLE
D) result in improved device performance. We investigated the electronic st
ructure of LiF coated Al and Pt electrodes by x-ray photoemission spectrosc
opy (XPS) and ultraviolet photoemission spectroscopy (UPS). Thin LiF films
were grown in several steps onto Ar+ sputtered Al and Pt foils. After each
growth step the surfaces were characterized in situ by XPS and UPS measurem
ents. After evaluating band bending, work function and valence band offset
for both samples, their band lineups were determined. Our measurements indi
cate that despite the insulating character of LiF in both samples, band ben
ding is present in the LiF layer. The difference in band bending between th
e samples allows the conclusion that the driving force for the development
of the band bending results from the contact potential between the metal an
d the LiF overlayer. The band bending is most likely caused by a redistribu
tion of charged Frenkel or Schottky type defects within the LiF layer. The
work function of both samples after LiF deposition was dramatically lowered
compared to the values obtained on the clean sputtered metal surfaces. (C)
1998 American Institute of Physics. [S0021-8979(98)01624-7].