Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films incorporating Pt nanoparticles were synthesized by a simple method using H(2)PtCl(6)center dot xH(2)O. The surface morphology, chain structure, bonding states, and electronic structure of the films were investigated. Unusual formation of a PEDOT-rich surface was accompanied with interactions between PEDOT:PSS and Pt nanoparticles due to agglomeration of PEDOT:PSS around Pt nanoparticles and destabilization of chain conformation. High doping of the PEDOT moiety occurred during the reduction of H(2)PtCl(6)center dot xH(2)O so that an increased work function and a decreased energy gap between the edge of the highest occupied molecular orbital and the Fermi level were observed. Intermediate products including chlorine and [PtCl(6)](-), and the ionic nature of the Pt nanoparticles were responsible for the resultant properties of Pt-PEDOT:PSS. Products generated during the formation of Pt nanoparticles served as a third anionic dopant like PSS and as an inhibitor of segregation. (C) 2010 Elsevier B.V. All rights reserved.