Síntese e caracterização de óxido de grafeno e aplicações em eletrônica orgânica

Abstract

In this thesis, we explore the synthesis and characterization of graphene oxide (GO) for Organic Electronic applications using the modified Hummers’ method. GO nanosheets thin films were obtained using the sprayer technique deposition and were further reduced using a combination of chemical and thermal treatments. High-quality films are normally obtained with thermal treatment at temperatures about 1000 °C, while the highest temperatures employed during the thermal treatment in this work were as low as 400 °C, which is a mandatory condition when dealing with organic electronic devices on glass substrates. To reach such a low thermal treatment, a two-step oxidation process was employed in order to allow the formation of carbonyl chemical groups rather than epoxy functionalization. Each GO sample was structurally and chemically analyzed by infrared spectroscopy (ATR-FTIR), x- ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-VIS), thermogravimetric analysis (TGA), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The GO conducting thin films exhibited a sheet resistance of 3.2x103 ohm/sq as well as a high transmittance: up to 80% at 550 nm. Furthermore, Raman spectroscopy, xray diffraction and AFM show that the thermally reduced thin films are mainly composed of single and bilayer GO nanosheets with a very low average roughness. These thin films have been employed as transparent anodes in organic light emitting diodes (OLEDs). Also, GO thin films were used as hole transport layer (HTL) in organic photovoltaic devices. Surprisingly, we observed an increase of 20% in the efficiency of the devices compared with those fabricated using PEDOT:PSS as HTL. The increase in the performance was attributed to the stoichiometric composition observed on the as prepared GO using the route described in this work.