Fraunhofer FEP Develops Roll-to-Roll Plasma Process for Graphene

Graphene layers promise great progress and increased efficiency in solar applications, energy storage and smart glass applications due to their outstanding properties, including transparency, barrier effect and conductivity.

The lack of scalable deposition processes with consistently high layer quality at cost-efficient throughputs has so far prevented the breakthrough of this promising material.

As part of the funded EU project NewSkin (GA No. 862100), the Fraunhofer Institute for Electron Beam and Plasma Technology FEP has developed an innovative PECVD process that enables the deposition of graphene at high process speeds and offers higher production throughputs and a wider range of substrates at lower process temperatures.

The researchers will present the process at Manufacturing World Tokyo from June 19 – 21, 2024 at booth No. E 53-11 in Tokyo, Japan.

Graphene has the potential for outstanding performance gains in solar cells, organic light-emitting diodes (OLEDs), electrical energy storage devices or smart windows and even membranes, e. g. for seawater desalination. Its phenomenal properties are impressive: the material is transparent, lightweight, and stronger than steel. Graphene also has a high electrical and thermal conductivity and is very flexible.

Researchers have been working on the integration of graphene as a transparent electrode in photovoltaics or in OLEDs, e. g. for curved touchscreens or to increase the efficiency of solar cells for several years. Due to its high electrical conductivity, the integration of graphene into energy storage devices such as batteries or supercapacitors is a promising approach to enhance charging and discharging cycles.

So far, scalability issues have been a bottleneck in getting graphene into applications. In addition, the integration of graphene into existing manufacturing processes is a technical challenge.

Recently, Fraunhofer FEP researchers have made progress in a new technology for the synthesis of graphene using PECVD (Plasma Enhanced Chemical Vapor Deposition). As part of the funded EU project NewSkin (Grant Agreement No. 862100) Fraunhofer FEP has demonstrated a proof of concept for a pioneering low-cost graphene deposition process.

Current synthesis processes for graphene require the application of high temperatures and the use of catalysts. On the other hand, scientists at Fraunhofer FEP are utilizing plasma-assisted processes. This allows the parameter window for the synthesis of graphene to be significantly expanded, so that deposition is also possible at lower substrate temperatures and higher throughputs at the same time.

“Graphene can be deposited on metallic strips using the innovative PECVD process in the roll-to-roll mode,” said Dr. Stefan Saager, group leader for coating metal and energy technology. “In the first step, the metal strip is coated with a thin layer of a catalyst material such as copper in vacuum. This allows the desired substrate material to be selected independently of the suitable catalyst material.

“The coated metal strip is then fed into a process unit containing an argon plasma. Its argon ions collide with the substrate and heat it efficiently in a very short time. By adding suitable precursor gases such as methane or acetylene, the respective molecules can be cracked into their constituents and partially ionized at the same time. Ideally, the resulting carbon atoms and ions are deposited on the substrate in a monolayer, well-ordered 2D structure, thus synthesizing the desired layer of graphene.”

Using the newly developed PECVD process, researchers at Fraunhofer FEP have already been able to synthesize graphene layers on metal strips with a width of 280 mm at a strip speed of one meter per minute.

In the next step, the scientists at Fraunhofer FEP are going to work on the reproducibility of the results and on the further improvement of the layer properties, e. g. the number of graphene layers.