Effect of bending deformation on photovoltaic performance of flexible graphene/Ag electrode-based polymer solar cells

Abstract

The current work describes a simple low cost solution-based method to synthesis graphene silver (Gr/Ag) nanocomposite as electrode material in fabrication of flexible polymer solar cells (PSCs). Flexible and transparent Gr/Ag – based electrodes were easily prepared on a desired scale by spin coating of an aqueous solution of Gr/Ag nanocomposite on polyethylene terephthalate (PET) substrate at ambient conditions. With the optimization of the weight ratio of Gr/Ag and the electrode thickness, flexible electrodes with sheet resistance of as low as 83 kΩ sq⁻¹ and transmittance of 47% were achieved. These electrodes were then utilized as transparent anodes in the fabrication of flexible PSC devices, replacing ITO. Photovoltaic performance of the fabricated devices was evaluated as a function of the anode electrode thickness under three conditions; at rest, inward bending and outward bending. The introduction of Ag into Gr resulted in a significant improvement in open circuit voltage (V_OC), short circuit current density (J_SC) and power conversion efficiency (PCE) compared to that considered for Gr-based devices. The Gr/Ag-based devices showed J_SC of 1.46 mA cm⁻² and a V_OC of 0.71 V. Under bending, PSC devices showed considerably larger V_OC and J_SC compared to the rest position. Furthermore, PCE of the devices decreased about 5.6% when they were bent inward and increased about 34% as they were bent outward. This was in good agreement with the observed changes in the sheet resistance of the fabricated flexible electrodes under similar conditions. The advantages of the described method for fabrication of flexible transparent electrodes include simple solution-based process, production of Gr-based electrodes with high mechanical stability via a low cost and environmentally friendly method and finally, the compatibility and adaptability of the method with roll-to-roll manufacturing technique suitable for industrial production.