Investigation of the interfaces formed between ITO and metal phthalocyanines (NiPc and CoPc) by photoelectron spectroscopy

The interfaces formed between metal phthalocyanines (NiPc and CoPc) and ITO were studied by X-ray and Ultra-Violet Photoelectron Spectroscopies (XPS and UPS, respectively). The results showed the formation of an interfacial dipole in both cases (NiPc/ITO, CoPc/ITO) in different direction due to the different electronic properties of the organic materials. This was evidenced by the shift of the XPS organic related peaks as well as the change of the vacuum level position. A broadening of the HOMO feature at the early steps of deposition, compared to the bulk organic layers, was also observed. The HOMOcut-off position for the NiPc overlayer was found to be at 1.00 ± 0.05 eV of binding energy from the Fermi level of the energy analyser and at 0.80 ± 0.05 eV for the CoPc layer, respectively. A comparison between ITO and polycrystalline Au foil as substrates in interfaces with MePcs (NiPc, CoPc) is also discussed.