Controlled p-doping of zinc phthalocyanine by coevaporation with tetrafluorotetracyanoquinodimethane: A direct and inverse photoemission study

P-doping of zinc phthalocyanine (ZnPc) with tetrafluorotetracyanoquinodimet hane (F-4-TCNQ) is investigated with ultraviolet and x-ray photoemission sp ectroscopy, inverse photoemission spectroscopy, and in situ current-voltage (I-V) measurements. The electron affinity of F-4-TCNQ (5.24 eV) is found t o be equal, within experimental error, to the ionization energy of ZnPc (5. 28 eV), consistent with efficient host-to-dopant electron transfer. As a re sult, the Fermi level in doped ZnPc drops from near midgap to 0.18 eV above the leading edge of the highest occupied molecular orbital and a narrow sp ace-charge layer (< 32 <Angstrom>) is formed at the interface with the Au s ubstrate. In situ I-V measurements show a seven orders of magnitude doping- induced increase in hole current. (C) 2001 American Institute of Physics.