Electronic structure of graphene films prepared from water dispersions and their energy level alignments with organic semiconductors

Abstract

The unique physical and chemical properties of graphene offer significant potential in a wide range of applications, particularly as a flexible electrode in electronic devices. Solution-processable graphene, especially graphene dispersion in water (GDW), has emerged as a promising candidate for cost-effective, environmentally friendly, and large-scale production. However, the energy level alignment between GDW and semiconductors, which is critical for designing efficient device architectures, remains insufficiently understood. In this study, we investigated the interfacial electronic structures of GDW electrodes with organic semiconductors (C60 and rubrene) using in situ x-ray/ultraviolet photoelectron spectroscopy. We also explored the effect of ultraviolet–ozone (UV–O3) treatment on the charge injection barriers. After 5 min of UV–O3 treatment, the work function of GDW increased by ∼0.4 eV due to surface oxidation, shifting the electron and hole injection barriers for C60 from 0.59 and 1.66 eV to 0.84 and 1.41 eV, respectively, and shifting those for rubrene from 1.82 and 0.74 eV to 2.14 and 0.42 eV, respectively. Weak interactions of both organic semiconductors with the GDW were observed, in contrast to metal electrodes. These results provide valuable insights into the design of future high-efficiency devices using GDW.