Bio-Inspired Catecholamine-Derived Surface Modifier for Graphene-Based Organic Solar Cells

Abstract

Owing to the growing interest in next-generation solar cells as a clean and renewable energy source, the demand for alternative transparent conducting electrodes (TCEs) has also increased. Although indium tin oxide (ITO) has been widely used as the standard TCE, its chemical and mechanical instabilities limit its widespread use in emerging photovoltaics. Graphene has attracted much attention as a potential alternative TCE owing to its excellent physical, optical, and electrical properties. However, owing to the inert nature of graphene with a hydrophobic surface, a significant amount of research has been devoted to resolve the nonwetting issue of charge-transporting materials on graphene. In this study, a thin layer of norepinephrine, an amphiphilic catecholamine derivative, was applied to graphene as a hydrophilic surface modifier to enable efficient surface modification without significantly decreasing the optical transmittance or the electrical conductivity. This modification allowed a commonly used hole-transporting material to be applied uniformly to the surface. Thus, the power conversion efficiency (PCE) of organic solar cells (OSCs) fabricated with this poly(norepinephrine)-coated graphene electrode was 7.93%, which is approaching close to that of the ITO-based reference device with a PCE of 8.73%. This work represents the first demonstration of an adhesive biomaterial as an efficient surface modifier for chemically inert graphene and its successful application in OSCs, which shows promise for the future development of bio-inspired graphene systems for applications to various optoelectronic devices.