Sprayed organic photovoltaic cells and mini-modules based on chemical vapor deposited graphene as transparent conductive electrode

Chemical Vapor Deposited (CVD) graphene is one of the most interesting candidate to replace indium tin oxide (ITO) as transparent conductive electrode in organic photovoltaic field. Here, a four-layer graphene has been properly doped to decrease the sheet resistance down to 30 Ohm/sq and treated with PEDOT:PSS to make it compatible with the typical solution processing of this photovoltaic technology. The functionalized graphene has been applied as cathode in inverted polymer solar cells fabricated by spray coating the active layer and the transport layers. A significant power conversion efficiency of 3.1% has been achieved, not far from the reference ITO-based cells. All the process has been carried out by using commercial materials and industry-compatible solvents. Moreover, the preliminary results on the first application of graphene electrode in a module are reported. The active area of the module is 1.6 cm2. The electrical functionality of the module demonstrates the high quality of graphene over relatively large area and, combined with the spray technique used for the deposition of the layers, shows the potential for a real ITO-free scale-up of organic photovoltaics.