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 $(ϕ)$ values before organic deposition were $∼4.7eV$ (exposed to air), $∼5.2eV$ (atomically clean), and $∼5.5eV$ (UV∕ozone treated). The high $ϕ$ obtained for $UV∕O3$ 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 $1.4eV$ (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.