Changes in the Electronic Structure of Tetra-Tert-Butyl Copper Phthalocyanine Film by Ultraviolet-Ozone Treatment

Ultraviolet-ozone (UVO) treatment modifies the surface properties of film for use in thin-film optoelectronics. In particular, the hydrophobic nature of the surface of organic films can be changed to a hydrophilic nature, thereby enabling a multilayer structure using a solution process. However, the electronic structure of organic films with UVO treatment has not been investigated in detail. In this study, the changes in the electronic structure of tetra-tert-butyl copper phthalocyanine (ttb-CuPc) films by UVO treatment were explored using UV-vis absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). The ttb-CuPc film was fabricated by spin coating, and various UVO treatment times were applied. As the UVO treatment time increased, the absorption intensity of the ttb-CuPc films exponentially decayed. In the XPS spectra, the oxidation process was observed in two stages (macrocyclic isoindole units followed by peripheral ttb units). Upon oxidation, while the C and N atoms in the ligands exhibited an electron-donating characteristic, the central Cu atom showed an electron-withdrawing nature. Such an altered charge distribution on the ttb-CuPc molecule can significantly influence charge transport in optoelectronic devices.