Graphene oxide (GO) was synthesized using modified Hummers method. GO films were deposited by doctor blade onto glass slides and Ecoflex® membranes using GO suspensions, or dip-coated onto molecular functionalized glass substrates. Doctor bladed films were studied by optical transmittance, linear sweep voltammetry and by thermal imaging under applied potential. Dip coated films were reduced with different chemical agents to produce transparent, conductive, reduced graphene oxide (rGO) films that were characterized by optical transmittance, current sensing atomic force microscopy and X-ray photoelectron spectroscopy. Doctor bladed GO films were mechanically stable, with resistances ranging 10 6 to 10 11 ohm depending on the film thickness, which in turn depended on the GO precursor solution concentration. Thermal imaging did not provided evidence of visible voltage-activated conduction. The best reduction treatment to obtain transparent and conductive rGO films comprised a primary reduction with NaBH4 followed by an air annealing at 120 ºC. Conductive atomic force microscopy indicated that rGO film conductivity is governed by the superposition of individual sheet and X-ray photoelectron spectroscopy suggested that the C/O ratio is not determinant for conduction. The better-reduced films had transmittances ca. 85% with sheet resistances around 10 3 ohm/sq, making them feasible as transparent electrodes. Finally, a short discussion about location of GO/rGO in organic solar cells is presented.

Graphical Abstract

Optical and electrical properties of graphene oxide and reduced graphene oxide films deposited onto glass and Ecoflex® substrates towards organic solar cells