UV/ozone treated Au for air-stable, low hole injection barrier electrodes in organic electronics

Ultraviolet and x-ray photoelectron spectroscopies were used to study electronic properties of interfaces between Au substrates and a number of organic semiconductors (small molecules and polymers). Au surface work function (phi) values before organic deposition were similar to 4.7 eV (exposed to air), similar to 5.2 eV (atomically clean), and similar to 5.5 eV (UV/ozone treated). The high phi obtained for UV/O-3 treated Au was due to Au oxide formation and surface-adsorbed carbon and oxygen species. Au surface morphology remained essentially unchanged by UV/ozone exposure, as observed by atomic force microscopy. Hole injection barriers (HIBs) at interfaces between UV/ozone treated Au and the organic semiconductors were systematically lower than those for untreated Au (both atomically clean and air exposed). Reductions in HIB of up to 1.4 eV (for p-sexiphenyl) were achieved. In addition, good long-term stability of reduced HIBs of such interfaces was observed for air storage of up to several days. (c) 2006 American Institute of Physics.