Influence of water on the work function of conducting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)

The influence of water exposure on the work function (phi) and surface composition of conducting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDT:PSS) was investigated with ultraviolet and x-ray photoelectron spectroscopies. It was found that annealing PEDT: PSS in vacuum to 220 degrees C yields a high phi of 5.65 eV. Subsequent exposure to water vapor or air reduces phi to similar to 5.15 eV, and the film surface becomes enriched with PEDT. These observations were fully reversible for repeated annealing-water exposure cycles. The reduction in phi is attributed to (i) the inclusion of water leading to a larger dielectric constant and (ii) polymer swelling-induced rearrangements of surface dipoles. (c) 2007 American Institute of Physics.