An increase of work function （0.3 eV） is achieved by irradiating poly（3,4-ethylenedioxythiophene）：poly（styrene sul- fonate） （PEDOT：PSS） film in vacuum with 254-nm ultraviolet （UV） light. The mechanism for such an improvement is investigated by photoelectron yield spectroscopy, X-ray photo electron energy spectrum, and field emission technique. Sur- face oxidation and composition change are found as the reasons for work function increase. The UV-treated PEDOT：PSS film is used as the hole injection layer in a hole-only device. Hole injection is improved by UV-treated PEDOT：PSS film without baring the enlargement of film resistance. Our result demonstrates that UV treatment is more suitable for modifying the injection barrier than UV ozone exposure.
We describe a simple method to increase the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)film by exposure to ultraviolet(UV)light in vacuum.Up to four order of conductivity improvement(from 10 3to 50 S/cm)is achieved by irradiating PEDOT:PSS film with 254 nm ultraviolet(UV)light.Increased conductivity in UV treated PEDOT:PSS film is stable under ambient exposure.The mechanism for conductivity improvement is investigated by current-voltage measurement,atomic force microscopy,and absorption spectrum.Photo-cross-linking of PSS chains is determined as the reason for conductivity improvement.Our result demonstrates that UV treatment is capable of modifying the conductivity of PEDOT:PSS film independent of the process of film formation.
