The effect of UV ozone treatment on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)

The interface between ultraviolet (UV) ozone treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and N,N'-diphenyl-N,N'-bis-(1-naphthyl)-1-1'-biphenyl-4,4'-diamine (alpha-NPD) was investigated using single carrier hole-only devices and in situ ultraviolet and x-ray photoelectron spectroscopy to elucidate the implications for device applications. It is found that although the work function of PEDOT: PSS is increased by UV ozone treatment, the injection barrier to alpha-NPD is in fact increased, resulting in lower current density in devices. The apparent increase in work function is attributed to a metastable surface dipole as a result of UV ozone treatment, which does not significantly influence the energy-level alignment. (C) 2009 American Institute of Physics. [doi:10.1063/1.3257382]