Application of solvent modified PEDOT:PSS to graphene electrodes in organic solar cells

Graphene has been proposed as a promising transparent conducting electrode material in organic photovoltaic (OPV) solar cells to substitute the widely used indium tin oxide (ITO). Various studies have reported OPV devices with graphene electrodes showing comparable performances to ITO-based OPV cells. However, the fabrication reliability or device yield has not been widely discussed. In our investigation it was found that graphene-based OPVs tend to have much lower device yield than the ITO-based ones if similar fabrication processes are used. One possible reason could be due to the challenge faced in obtaining a uniform coating of PEDOT:PSS hole injection layer (HIL) on graphene. In fact, several attempts have been made to overcome this challenge. In this work, we report a facile method of solvent modification of PEDOT:PSS to achieve a homogeneous coating on graphene. A significant enhancement in the device yield was observed as compared to devices using normal aqueous solution based PEDOT:PSS; nevertheless, it was still only ∼50%. Further improvement was made by adding an additional electron blocking layer (EBL), molybdenum trioxide, after the coating of PEDOT:PSS. The observation in this work calls for further investigation to understand the role played by the HIL or EBL in graphene-based OPV devices.