Modification of the electrical properties of PEDOT:PSS by the incorporation of ZnO nanoparticles synthesized by laser ablation N.G. Semaltianos a, * , S. Logothetidis a , N. Hastas a , W. Perrie b , S. Romani b , R.J. Potter b , G. Dearden b , K.G. Watkins b , P. French c , M. Sharp c a Department of Physics, Aristotle University of Thessaloniki, Thessaloniki GR-54124, Greece b Department of Engineering, University of Liverpool, Brownlow Hill, Liverpool L69 3GH, UK c General Engineering Research Institute, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK article info Article history: Received 3 September 2009 In final form 24 November 2009 Available online 26 November 2009 abstract Laser ablation of a solid target in a liquid environment offers an easy, fast, and environmentally friendly method for the generation of nanoparticles with desired properties. In this Letter we report modification of the electrical properties of PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)) by the incorporation into it of ZnO nanoparticles which were synthesized by laser ablation. By forming the nanocomposite, change of the chemical structure of the polymer from a mixture of benzoid and quin- oid to a mostly quinoid and a conformational change of the polymer chains from coil to expanded-coil or linear was observed. Furthermore, these changes result in an increase by almost twice of the electrical conductivity of the polymer. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction PEDOT:PSS (poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate)) is an organic material which is com- monly used as the anode electrode (hole injection/transport layer) in organic electronic devices such as light emitting diodes, field ef- fect transistors and photovoltaic cells [1,2]. It is easily processable from aqueous solution, has high strength and flexibility, excellent thermal, mechanical and environmental stability and high trans- parency in the visible range. It replaces the traditionally used in- dium tin oxide (ITO) usually in the case of flexible organic electronic devices or it can be used as a buffer layer on top of ITO to smooth its surface and improve device stability [2,3]. The electrical conductivities of thin films spin-coated from com- monly used types of PEDOT:PSS such as pure PH500 were reported to have values of up to 1 S/cm which is by more than two orders of magnitude lower than the conductivity of ITO (8000 S/cm) [3,4]. Traditional methods to increase the conductivity of PEDOT in- cluded in the past the addition of DMSO (dimethyl sulfoxide) or DMF (N,N-dimethylformamide) to the polymer [3,5,6], a compound with two or more polar groups such as glycols (EG, DEG or TEG), meso-erythritol, methyl sulfoxide, 1-methyl-2-pyrrolidinone or 2-nitroethanol [7–10] or anionic surfactants [11]. Lately a maxi- mum conductivity of 570 S/cm was reported for the PEDOT:PSS PH750 modified with 5% DMSO and 13% isopropanol [12] while the PEDOT:PSS PH500 modified with 5% DMSO and 13% isopropa- nol showed a conductivity of 330 S/cm [4,12]. Very recently H.C. Starck has also produced a PEDOT:PSS (CLEVIOS™ PH1000) with a minimum conductivity of 900 S/cm (after again the addition of 5% of DMSO) [13]. In the evolution of the field of organic electronics, incorporation into polymer matrices of inorganic or metallic nanoparticles (NPs), in general, with the resulting formation of polymer–NPs compos- ites (hybrid materials, nanocomposites) seems as an attractive method for the modification of the properties of polymers which are commonly used in the fabrication of organic optoelectronic de- vices, for improved performance [14]. This method combines the large variety of organic polymers which are solution-processable with the excellent electronic and optical properties of NPs. Due to its unique optical and electrical properties as an inor- ganic material for optoelectronic applications combined with its intoxicity and relatively large abundance at low cost, ZnO in the form of NPs has been used for the formation of hybrid materials which are used mainly as active layers in organic devices [15– 18] and in the form of nanorods, in a smaller degree, for the mod- ification of the properties of the device anode layer (PEDOT:PSS) [19]. The ZnO NPs or nanorods which have been utilized so far for the fabrication of nanocomposites, have been usually synthe- sized by sol–gel colloidal chemical methods involving hydrolysis and condensation of zinc acetate dihydrate by potassium hydrox- ide in alcoholic solution under basic conditions [20–22] or mixing zinc acetate dihydrate with the polymer polyvinylpyrrolidone fol- lowed by water evaporation and finally calcination of the dried mixture [19,23]. These methods usually require high temperatures and long reaction times for the synthesis of nanomaterials. 0009-2614/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2009.11.054 * Corresponding author. E-mail address: semal@physics.auth.gr (N.G. Semaltianos). Chemical Physics Letters 484 (2010) 283–289 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett