In situ reduction of Graphene oxide into polymer for Photovoltaic Application

n this work the effectiveness of different methods for green in situ reduction of graphene oxide were investigated. Aiming at enhancing the electrical conductivity of polymeric matrices for photovoltaic (PV) application. Graphene is a 2-D single layer of sp2-bonded carbon atoms characterized by high specific surface area, Young’s modulus, thermal stability, mobility of charge carriers and plus fascinating transport phenomena such as the quantum Hall effect [1]. These unique physical and chemical properties massively improve the electrical conductivities, transparency, and flexibility of graphene-including materials, thus capturing the interest of researchers in the field of solar cells. In this frame, graphene based nanocomposites or thin films have been recently exploited as transparent electrodes, electron and hole transporting layers [2]. Among the several methods, including chemical vapor deposition (CVD) and mechanical exfoliation, the chemical reduction of graphene oxide (GO) is regarded as the most promising for the large-scale production and solution processability of graphene. Thanks to the presence of hydroxyl and epoxide groups at the surface of the basal planes and carbonyl groups at the edges, GO can be dispersed in aqueous solution. In addition those functionalities promote linking with polymeric matrices to create a continuous interconnected phase [3]. However, these functional groups could decrease the electrical properties of graphene thus hindering the mobility of charge carriers; consequently the reduction of GO is deemed necessary aiming at PV applications. In this work, GO prepared by a modified Hummers method was used [4]. Several methods to reduce in situ graphene oxide into different polymeric matrices were investigated as function of nanocomposites composition. The aim of this screening was finding the most suitable method for implementing such nanocomposites into photovoltaic devices of different nature (perovskite solar cells, colloidal nanocrystals-based solar cells). Nanocomposites films were obtained by spin coating onto different substrates and characterized by several techniques, such as UV-visible spectrophotometry and X-ray photoelectron spectroscopy (XPS). The microstructure of the films was characterized by X-ray diffraction. Graphene-based nanocomposite surface morphology was investigated by scanning electron microscopy and atomic force microscopy. The resistivity of composite films was measured with a four-point probe method. Moisture permeation measurements were carried out using a permeabilimeter. Finally the film with the better properties was implemented in a hybrid solar cell to evaluate the impact on the device performance. Acknowledgments This work was financially supported by Caripuglia