Flexible electrochromic films based on CVD-graphene electrodes

Abstract

Graphene synthesized via chemical vapor deposition is a notable candidate for flexible large-area transparent electrodes due to its great physical properties and its 2D activated surface area. Electrochromic devices in optical displays, smart windows, etc are suitable applications for graphene when used as a transparent conductive electrode. In this study, various-layer graphene was synthesized via chemical vapor deposition, and inorganic WO(x) was deposited on the layers, which have advantageous columnar structures and W(6+) and W(4+) oxidation states. The characteristics of graphene and WO(x) were verified using optical transmittance, Raman spectroscopy, x-ray photoelectron spectroscopy and scanning electron microscopy. The optimum transparent conductive electrode condition for controlling graphene layers was investigated based on the optical density and cyclic voltammetry. Electrochromic devices were fabricated using a three-layer graphene electrode, which had the best optical density. The graphene in the flexible electrochromic device demonstrated a potential for replacing ITO in flexible electronics.

Graphene as Transparent Electrodes: Fabrication and New Emerging Applications

“…In order to utilize CVD graphene as TEs, it must be separated from the metal catalyst and transferred onto the target substrates. [14a],…”

“…Transfer : To form the CVD graphene‐based TEs, the transfer step is required to separate graphene from the catalyst metal and move it to arbitrary substrates, such as PET, glass, and SiO 2 /Si. [14a], Generally, the transfer methods for CVD graphene can be classified into four types including polymer‐supported transfer, mechanical exfoliation, continuous transfer via roll‐to‐roll process and transfer‐free techniques as summarized in Table . [7d]…”

“…Moreover, other kinds of supporting polymers such as fluoropolymer, conductive polymers, e.g., poly(3,4‐ethylene­dio­xythiophene):poly(styrenesulfonate) (PEDOT:PSS),[[40b],[46b] have also been investigated to provide both excellent supporting layer and residue‐free transfer methods. [40b], As can be seen in Figure A‐b, certain polymer film (e.g., PEDOT:PSS) was used not only as the supporting layer but also directly as the target substrate. Meanwhile, stable efficient doping of the GTEs was simultaneously reached by applying the PEDOT:PSS layer.…”

“…After the transfer process, the graphene/polymer electrode was ready to be used as a TE without any further removing or cleaning steps. [40b],[46b]…”

“…The quality of as‐deposited graphene films on a target substrate can be characterized in many ways. For GTEs, optical transmittance and sheet resistance are the two most crucial criteria to evaluate graphene films grown via different synthesis and fabrication methods[7a],[14c],[40b] (Tables and ). Other properties, such as surface properties, optical anisotropy, work function, mechanical properties, processibility, stability and production cost are also important factors for evaluating a candidate material for use as the TEs .…”