The influence of water exposure on the work function (ϕ) 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°C yields a high ϕ of 5.65eV. Subsequent exposure to water vapor or air reduces ϕ to 5.15eV, and the film surface becomes enriched with PEDT. These observations were fully reversible for repeated annealing–water exposure cycles. The reduction in ϕ is attributed to (i) the inclusion of water leading to a larger dielectric constant and (ii) polymer swelling-induced rearrangements of surface dipoles.

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