Relationship between electrical and thermal conductivity in graphene-based transparent and conducting thin films M. Shafiq Ahmed a , Sabastine Ezugwu a , Ranjith Divigalpitiya b , Giovanni Fanchini a,c, * a Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond St., London ON N6A 3K7, Canada b 3M Canada Company, 1840 Oxford St., London ON N5V 3R6, Canada c Department of Chemistry, University of Western Ontario, 1151 Richmond St., London ON N6A 5B7, Canada ARTICLE INFO Article history: Received 18 September 2012 Accepted 21 May 2013 Available online 30 May 2013 ABSTRACT We measured and modeled the electrical, optical and thermal properties of transparent and conducting thin films based on graphene and graphitic platelets. Thermal conductivity of our films decreases with increasing electrical conductivity. Our experiments indicate that, for sufficiently large platelets, the influence factor in controlling the thermal conduc- tivity is represented by the junctions between neighboring graphene platelets. The thick- ness of such junctions is determined by the average number of graphene layers (N) forming each platelet. The fact that both the thermal and electrical properties depend on N allows us to establish a model that leads to a theoretical relationship between the ther- mal and electrical conductivity in our samples, which is general enough to be applied to a large class of graphene-based thin films. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The exceptional thermal properties of graphene-based nanomaterials make them commercially viable for thermal management [1]. Graphene, an individual layer of carbon atoms, was shown to possess thermal conductivity up to 5000 W m 1 K 1 [1], with high optical transparency and excel- lent electrical properties [2–4]. Incorporation of small quanti- ties of graphitic nanoplatelets and graphene flakes into epoxy resins significantly improve the thermal conductivity of these materials [1,5,6]. While transparent and conducting carbon- based films (TCCF) prepared from graphene platelets are not as of yet competitive with indium-tin oxide (ITO) as transpar- ent electrical conductors, they are superior to ITO for thermal management applications, since the thermal conductivity of ITO is quite low (5.9 W m 1 K 1 ) [7]. Interestingly, the thermal properties of single-layer graphene are also retained, to a large extent, in thin graphite multilayers [3], TCCF and insu- lating nanocomposites including small amounts of graphene [4] and are preserved even when few-layer graphene and thin graphite are placed on a substrate [8]. However, a physical model describing the thermal properties in TCCF and related composite materials is still missing. While the thermal properties of ITO at room temperature are determined by the electronic band structure (and, there- fore, related to the electrical conductivity via the Wiede- mann–Franz law) the thermal properties of graphene-based materials are dominated by lattice vibrations [1,9], which makes the relationship between the thermal and electrical conductivity more complicated to be determined. Little at- tempt exists in the literature to determine such relationship as a function of the average number of layers and the fraction 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.05.041 * Corresponding author at: Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond St., London ON N6A 3K7, Canada. E-mail address: gfanchin@uwo.ca (G. Fanchini). CARBON 61 (2013) 595 – 601 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon