Fabrication and Applications of Graphene Oxide-Based Thin Films

Abstract

New approach for fabrication of reduced graphene oxide (rGO) multilayers which can be used for transparent and conducting thin films was developed. This was achieved by using layer-by-layer (LbL) assembly of positively and negatively rGO sheets which could provide highly controllable thin films in terms of thickness, transmittance, and sheet resistance. In particular, the thickness of the multilayer thin films of rGO was able to be controlled precisely in the subnanometer scale by ~ 0.46 nm via simply varying the number of stacking layers. Therefore, this method enabled an excellent control of rGO multilayers over the optical and electrical properties which are related to thickness. Furthermore, we demonstrated the application of the rGO multilayers for an OLED device. The LbL assembly could successfully expand to integration of metal nanoparticles and GO sheets for hybrid films of GO/metal which can be used for transparent counter electrodes with improved conversion efficiency of DSSCs to replace the Pt. Very thin films of GO were fabricated through a layer-by-layer (LbL) assembly process with high controllability, and metal nanoparticles are then formed on the assemblies. The thin hybrid films of GO/Pt and GO/Au were still transparent and show a 9.5 and 7.1 % increase in efficiency when they were applied as a counter electrode for DSSCs as compared to DSSCs with conventional Pt counter electrodes. It is particularly interesting that Au in the form of hybrid films with GO can be utilized as counter electrodes since Au has not been applied in DSSC devices because it is easily etched away by iodide/triiodide in the electrolyte. Moreover, such GO/metal hybrid films could be applied with metals such as Cu, Ni, and Ag. These metals have not been used in DSSC systems for the reasons mentioned above regarding Au. Therefore, this GO/metal hybrid film as a counter electrode affords a chance for an even lower DSSC fabrication cost with high efficiency and transparency.