FERMI-LEVEL DETERMINATION IN ORGANIC THIN-FILMS BY THE KELVIN PROBE METHOD

We show that the Kelvin probe method (KPM) is well suited for ia situ measurements of the Fermi level of organic vapor-deposited dye layers. The method works well even for high resistivity materials, is nondest ructive. and does not need any top contacts. First results for zinc-ph thalocyanine (ZnPc) and perfluorinated ZnPc (ZnPc-F-16) are presented. The KPM results show that a 2.5% admixture of ZnPc-F-16 to a ZnPc mat rix leads to a 0.2 eV lowering of the Fermi level of ZnPc, i.e., ZnPc- F-16 has acceptorlike properties relative to ZnPc. (C) 1996 American I nstitute of Physics.