Hybrids composites of NCCO/PEDOT for thermoelectric applications Mario Culebras a , Antonio García-Barberá b , José F. Serrano-Claumarchirant b , Clara M. Gómez b, *, Andrés Cantarero a, * a Molecular Science Institute, University of Valencia, PO Box 22085, 46071 Valencia, Spain b Materials Science Institute, University of Valencia, PO Box 22085, 46071 Valencia, Spain A R T I C L E I N F O Article history: Received 28 September 2016 Received in revised form 14 December 2016 Accepted 15 December 2016 Available online xxx Keywords: Thermoelectrics Nanocomposites Conducting polymers Perovskites A B S T R A C T Organic materials are becoming a realistic roadway to fabricate efficient thermoelectric devices using environmental friendly materials. Such requirements are actually fulfilled by thermoelectric generators operating by conducting polymers, but also by hybrid materials. The combination of organic + inorganic compounds may exhibit a high electrical conductivity and Seebeck coefficient as well as lower thermal conductivity in order to efficiently generate thermoelectric power. In these hybrid compounds, perovskite-type oxides are a suitable election for the inorganic part since they have a high Seebeck coefficient although their electrical conductivity is usually low. Blending them with conducting polymers would be a good procedure to improve their thermoelectric properties. In this work, hybrids materials formed by a cobalt perovskite, Nd 1-x Ca x CoO 3 (NCCO), have been combined with the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with either poly(styrenesulfonate) (PSS) or tosylate (Tos). The electrical conductivity, Seebeck coefficient, X-ray diffraction and scanning electron microscopy have been used to characterize the resulting material. A thermoelectric power up to 1.0 mW/K 2 m has been obtained for NCCO/PEDOT:Tos at a 95/5 mass ratio. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The increasing energy demand in the World’s developing countries due to the economic growth, added to the energy curtail produced by the reservoir reduction of fossil fuels has accelerated the development of renewable energy resources. Particularly interesting is the use of thermoelectric (TE) devices, since a thermoelectric generator (TEG) is able to recover waste heat and directly converts it into electricity [1–4]. This phenomenon occurs by means of devices that work without fluids or moving parts making them compact and reliable compared to more conven- tional engines. However, to build a TEG with enough efficiency to be competitive when compared to other technologies (photo- voltaics, wind mills, hydraulic plants, etc), materials with a parameter termed figure of merit higher than unity is required [1,5]. The value of the dimensionless figure of merit (ZT) at a constant temperature depends on the Seebeck coefficient, S, the electrical conductivity, s, and the thermal conductivity, k, that is: ZT = (S 2 sT)/k. Semiconductor compounds and alloys such as: Bi 2 Te 3 , PbTe, SiGe and others are being efficiently used in the last twenty years, mainly in high temperature applications [6–9], but several drawbacks have been encountered in most of these inorganic materials such as toxicity, raw material shortages or high costs of production. Clearly, alternative materials must be developed with similar or better ZT. On one hand, cobalt-oxide-based crystals like Na x CoO 2 , with layered structures and their derivative compounds have been considered extremely good thermoelectric materials achieving ZT values close to 1 or higher. Within this crystal family, we can stand out single crystals of perovskite-type based on transition-metal oxides such as Sr 1-x La x TiO 3 [10–13]. These kind of oxides offer large Seebeck coefficients, low electrical conductivity, and relatively low thermal conductivity, although they are not easily synthesizable. In the last years, organic semiconductors, in particular conducting polymers, are increasingly being employed in elec- tronic and optoelectronic applications such as: solar cells, transistors or supercapacitors [1–17]. They offer important advantages over traditional inorganic semiconductors such as material abundance, low weight, low cost, high toughness and elasticity. They present low thermal conductivity, with improved values of ZT, but unfortunately S and s are low [1]. In principle, the low electrical conductivity can be improved by doping [18,19], that * Corresponding authors. E-mail addresses: Clara.Gomez@uv.es (C.M. Gómez), Andres.Cantarero@uv.es (A. Cantarero). http://dx.doi.org/10.1016/j.synthmet.2016.12.016 0379-6779/© 2016 Elsevier B.V. All rights reserved. Synthetic Metals xxx (2016) xxx–xxx G Model SYNMET 15547 No. of Pages 5 Please cite this article in press as: M. Culebras, et al., Hybrids composites of NCCO/PEDOT for thermoelectric applications, Synthetic Met. (2017), http://dx.doi.org/10.1016/j.synthmet.2016.12.016 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/sy nmet