Researchers have been working on integrating graphene as a transparent electrode in photovoltaics or OLEDs for many years. For example, integrating graphene to improve the efficiency of curved touchscreens or solar cells. Due to its high electrical conductivity, integrating graphene into energy storage devices such as batteries or supercapacitors is a promising approach to improve the charge and discharge cycles. The large surface area also enables higher capacity and energy density, and the mechanical stability of the material contributes to the life and reliability of these storage devices.
© Fraunhofer FEP
Experimental setup for catalyst coating and graphene synthesis
Scalability has been a bottleneck in introducing graphene into applications to date. In addition, integrating graphene into existing manufacturing processes is a technical challenge.
Fraunhofer FEP has over 30 years of experience in developing coating systems with customized properties. The institute’s core competencies are electron beam and sputter technology as well as plasma surface technology, for example in the development of roll-to-roll processes for uniform thin films. Recently, Fraunhofer FEP researchers have made progress in a new technique for synthesizing graphene using plasma-enhanced chemical vapor deposition (PECVD). As part of the EU-funded project NewSkin (Grant Agreement No. 862100), Fraunhofer FEP demonstrated a proof of concept for a pioneering, low-cost graphene deposition process.
© Fraunhofer FEP
Overview of PECVD Synthesis Process for Graphene
Plasma process for more efficient production of graphene
Current graphene synthesis processes require high temperatures and the use of catalysts. In contrast, scientists at Fraunhofer FEP are using plasma-assisted processes. This significantly expands the parameter window for graphene synthesis, allowing simultaneous deposition at lower substrate temperatures and higher throughput.
Researchers at Fraunhofer FEP have taken advantage of the versatility of the inline coating tool MAXI to develop new processes. Depending on the maturity of the process, the versatile vacuum coating plant offers the possibility to run the process in sheet-to-sheet and roll-to-roll mode. Furthermore, the versatility of the MAXI process enables pilot production, providing good prerequisites for the development and scale-up of graphene deposition processes.
Dr. Stefan Sager, Group Leader Coated Metals and Energy Technology, explains the technology: “Graphene can be deposited on metal strips using an innovative PECVD process in roll-to-roll mode. In the first step, the metal strip is coated with a thin layer of a catalyst material such as copper under vacuum. This allows us to select the desired substrate material separately from the suitable catalyst material. The coated metal strip is then fed into a process unit with an argon plasma. The argon ions collide with the substrate and heat it efficiently within a very short time. By adding a suitable precursor gas such as methane or acetylene, the respective molecules are broken down into their constituent elements and partially ionized at the same time. Ideally, the resulting carbon atoms and ions are deposited on the substrate in a single-layer, well-ordered 2D structure, thereby synthesizing the desired graphene layer.”
Due to plasma ion assistance, the formation process can be realized at relatively low substrate temperatures compared to other state-of-the-art processes.
Researchers at Fraunhofer FEP have already been able to synthesize graphene layers on metal strips with a width of 280 mm using the newly developed PECVD process at a strip speed of 1 meter per minute. The process thus enables high production throughput and is associated with cost reductions in prospective production processes. In addition, the technology expands the range of substrate materials that can be used, opening up a wider range of applications.
Reproducibility and optimization are on the agenda
In the next step, scientists at Fraunhofer FEP will focus on further improving the reproducibility of the results and the layer properties, such as the number of graphene layers.
Another challenge in the development of new technologies is the precise control of plasma and temperature conditions for uniform layer quality and morphology. Future research will also focus on improving the winding process of hot strips and further expanding the current process parameters.
Fraunhofer FEP provides a solid basis for manufacturers in the electronics and renewable energy sectors as well as other technology companies and research institutes to further develop and scale up graphene coating processes by leveraging the results achieved, existing know-how and equipment. The new process and other Fraunhofer FEP capabilities will be presented at Manufacturing World in Tokyo.