Ethanol-CVD growth of large single-crystal graphene and graphene-based derivative for photovoltaic applications

Graphene is a flat monolayer of carbon atoms in sp2 hybridization that exhibits exceptional physical properties such as very low resistivity, high current density, high thermal conductivity, high electronic mobility and high transparency. Graphene has raised strong interest already starting since 2004, the year in which physicists Geim and Novoselov isolate it from a block of graphite for the first time. Today the research is focused on the use and integration of graphene in optoelectronic technologies and on the optimization of graphene quality obtained by Chemical Vapour Deposition in order to obtain single-crystal graphene films or large single-crystal graphene grains with appropriate physical and electronic properties. In this thesis, the graphene growth parameters in ethanol-CVD on flat copper foil were studied and optimized. Ethanol (C6H12O6) is preferred to methane because it is cheaper, safer and allows to obtain graphene films in a shorter time. Particular attention was paid to the transfer method of the graphene from the growth substrate to interest substrates by using the cyclododecane (C12H24) as support layer during all the transfer process. The produced graphene was characterized by Raman spectroscopy and electron and atomic force microscopy. Graphene films with different electronic properties were grown by varying the growth parameters in CVD, in particular the temperature. These graphene films were assembled to realize graphene on n-type silicon Schottky Barrier Solar Cells. A conductive few-layers graphene film grown at 1070°C was used as transparent electrode while a non-conductive graphene-based derivative (GBD) grown at 790°C was used as interlayer between the n-type silicon absorber and the electrode. The non-conductive interlayer reduced the effects of recombination at the interface between the two materials that form the Schottky junction, increasing the Schottky barrier height and the external quantum efficiency with optical bias and then improving the performance of the device.