Wide-range work-function tuning of active graphene transparent electrodes via hole doping

Graphene is regarded as a potential candidate to replace the transparent conductive (TC) electrodes that are currently used in various optoelectronic applications. However, there is still a lack of methods by which to achieve low sheet resistance (R_s) with stable doping and work functions with a wide range of tunability, which is significant for band alignment at the interface to enhance charge transport and thus to achieve higher device performance. We developed a novel strategy for preparing a TC electrode by doping layer-by-layer (LBL)-stacked graphene with AuCl₃, by which means an excellent TC performance (an R_s of 40 ohm sq^-1 at a transmittance (T) of 89.5%) and an extremely wide range of work-function tunability (∼1.5 eV) were successfully achieved. Moreover, a hybrid electrode prepared by transferring doped graphene onto a pre-patterned Cu metal mesh exhibited a low resistance of ∼4.9 ohm sq^-1. In addition, we monitored the long-term stability of AuCl₃-doped graphene for 6 months and also constructed a model for accelerated degradation testing. The relevant mechanism of charge transfer between the graphene and the dopants was characterized based on X-ray photoelectron spectroscopy (XPS) spectra to elucidate degradation observed after long-term testing. This work contributes a novel type of "active electrode"; the doped graphene film not only serves as a high-performance TC electrode but also provides a wide range of tunable work functions. The proposed active electrode is prepared using a scalable and facile doping process, which paves the way for its usage in applications such as optoelectronic devices.