Increased work function in PEDOT：PSS film under ultraviolet irradiation

An increase of work function (0.3 eV) is achieved by irradiating poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (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. Surface 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.