Graphene-Based Composites Advance Energy Storage and Solar Cell Absorbers

Graphene-based technologies hold immense promise for revolutionising energy storage and conversion, yet realising this potential demands overcoming significant hurdles. Researchers Etienne Quesnel, Frédéric Roux and Fabrice Emieux, alongside colleagues from CEA, Liten and the Technological Educational Institute of Crete , including Emmanuel Kymakis and George Volonakis , detail advancements made within the European Graphene Flagship project towards integrating graphene and related materials into practical energy devices. Their work, presented in this paper, explores innovative composite materials and surface technologies for applications ranging from hydrogen storage and solar cells to high-performance batteries and supercapacitors, demonstrating how strategic integration can maximise graphene’s benefits. By highlighting both achieved progress and remaining technical challenges, this research offers a crucial perspective on the future of graphene in the energy sector.

Experiments show that these materials, possessing high electrical conductivity and a substantial surface-to-weight ratio, are particularly well-suited for applications requiring charge storage, gas storage, and catalytic reactions. This work establishes the potential of 2D crystals to enhance the performance of batteries, supercapacitors, hydrogen storage tanks, fuel cells, and photovoltaic cells, moving beyond simple material replacement towards entirely new device concepts.

The research highlights the creation of printable inks as a key pathway to realizing next-generation electrodes for energy storage and conversion devices. This breakthrough unveils a comprehensive evaluation of the value added by these graphene-based technologies compared to current device performances, aligning with the Horizon 2020 goals of providing sustainable and competitive solutions for European industry. For photovoltaic electrodes, where thin layers and precise interface engineering are crucial, surface technologies were favoured, demonstrating a focus on practical implementation. The study presents selected experimental and modelling results, showcasing how these technologies can maximize the benefits of GRM integration and address existing technical challenges.
Researchers are targeting a low-cost, roll-to-roll photovoltaic technology capable of achieving stable solar cells with efficiencies exceeding 10%, alongside the development of advanced GRM-based electrodes and lightweight batteries with an energy capacity target of 3. Furthermore, the work emphasizes the importance of scalability and environmental friendliness in the development of these technologies, ensuring their viability for large-scale industrial adoption. The research team is actively working to define applicative objectives related to building, portable, and transport applications, demonstrating a clear vision for the future of graphene-based energy solutions. This study not only advances the fundamental understanding of GRM integration but also paves the way for disruptive innovations in the energy sector, promising a new era of efficient and sustainable energy technologies.

Graphene Composites, Laser Doping and Surface Control represent

For photovoltaic applications requiring thin films and interface control, the research team prioritised surface technologies, employing both conventional vacuum processes and innovative laser irradiation strategies. Each implemented technology’s potential was assessed through experimental results and modelling. The study pioneered a laser-based doping methodology and validated it using density-functional theory (DFT) calculations. To probe work function (WF) modifications induced by chlorine atoms, first-principles DFT calculations were performed on zig-zag and armchair graphene nanoribbons, both pristine and edge-functionalized with chlorine.

Researchers functionalized twenty-five percent of the edges of the modelled nanoribbons, fully optimising the structures to determine an energy gain of 0.3 eV per chlorine atom on zig-zag edges, while armchair edges exhibited marginal stability. The team then calculated total charge density and electrostatic potential differences (ΔV) to analyse WF changes, revealing ΔV as the key driver of WF modification. Calculations demonstrated WF shifts of 0.15 eV and 0.26 eV for zig-zag and armchair edges, respectively, qualitatively agreeing with observed WF modifications of 0.25, 0.3 eV when functionalising graphene structures with chlorine. These investigations extended to other functional attachments and graphene flakes of varying shapes and sizes, paving the way for a comprehensive model of WF modification by covalent functionalisation, which will be detailed in a forthcoming publication.

Furthermore, the work explored hybrid inorganic material/graphene compounds to optimise photovoltaic conversion, aiming for a roll-to-roll compatible graphene-based organic photovoltaic (OPV) device reaching 10% efficiency. Scientists fabricated quantum dot (QD)-graphene hybrid materials to combine QD optical properties with graphene’s transport capabilities, addressing the challenge of improving carrier mobility in QD close-packed films. The team adopted a solution-processable, covalent-linking approach, functionalising reduced graphene oxide (rGO) with short-chained linker molecules to achieve a large contact area and short distance between the materials, facilitating efficient carrier transfer. This methodology enables the creation of materials with tailored properties for advanced energy applications.

Graphene composites enhance energy storage and photovoltaics significantly

The team evaluated the potential of the implemented technologies through a combination of experimental studies and modelling, demonstrating how the integration of graphene-related materials (GRMs) can be optimized to achieve high performance. Specifically, the research aims to enable low-cost, roll-to-roll photovoltaic technologies capable of delivering solar cells with stable efficiencies exceeding 10%. In parallel, the study targets the development of 2D material–based composites for lightweight batteries, with an energy density goal of 300 Wh kg⁻¹. Significant progress has also been reported toward lighter hydrogen storage tanks, with a gravimetric hydrogen storage target of 5.5 wt%. Additionally, researchers documented advances in sustainable fuel cell technologies, aiming to reach a performance of 10 kW gPt⁻¹ while substantially reducing platinum usage.

Supported by detailed device modelling, the research strategy emphasizes the careful selection and functionalization of graphene raw materials prior to their integration into energy devices, a critical step for effective material engineering and for achieving performance gains over conventional technologies. While thin-film solar cells currently hold only about 9% of the market share, they have demonstrated maximum power conversion efficiencies of approximately 20%. The work underscores the urgent need for lower-cost solar technologies, targeting costs below 0.5 €/W, and focuses on emerging solutions such as organic photovoltaics, perovskite solar cells, and quantum dot devices enabled by scalable roll-to-roll manufacturing processes.

Graphene composites advance energy device performance significantly

The research highlights graphene’s ability to act as a scaffold for controlling the growth of functional nanocrystals from liquid precursors, benefiting fuel cell electrodes, hydrogen storage, and Li-ion battery anodes. Graphene integration can lead to functionalities such as well-dispersed platinum catalyst particles for enhanced fuel cell activity, reduced hydrogen desorption temperatures for storage, and improved lithium ion storage mechanisms in batteries. However, the introduction of high surface area materials like graphene can also present challenges, including irreversible capacity in batteries and potential nanocrystal re-aggregation. The authors acknowledge the need for further material engineering to control surface chemistry within GRM scaffolds and to manage the formation of the solid electrolyte interphase in batteries.