Taking graphene from the lab to the industry is advancing by the leaps, thanks to the coordinated pan-European effort undertaken by researchers in the Graphene Flagship. All 15 Work Packages (WPs) showcased their annual highlights in the result report recently published online. Even though it is undeniable that all research directions produced highly interesting and relevant results, the Flagship Director, Jari Kinarent, singles out two of these breakthroughs.
The first breakthrough was a planned one, a result of long-term, goal-oriented research. A prime embodiment of the Flagship goals and purpose, an optical photodetector and modulator showed record performance that will enable, for example, ultrafast data switches for 5G communications. The other breakthrough was a serendipitous discovery that few-layer graphene flakes destroy monocytes, which may find its use in treatment of leukemia. The Director used this example to point out that research cannot always be planned in detail, and that a basic research component must remain even when the focus shifts towards higher technology readiness levels.
The WP “Enabling Research” focuses on exploring new concepts and applying them to novel applications. One such application is in lithium-ion batteries that rely on transport of lithium ions between the active electrolyte and a solid electrode. The electrodes must be built from materials that conduct electricity but also allow the passage of ions. Researchers from the Max Planck Institute for Solid State Research and CNR have discovered that lithium ions readily penetrate between sheets of graphene in bilayer samples, pointing to an opportunity to exploit the excellent carrier mobility of multilayer graphene in novel electrodes. Improved electrode quality should give a new lease on life to lithium-ion batteries, the capacity of which has been under increasing strain due to the rise of high-power mobile computing devices, drones, and autonomous vehicles.
The “Spintronics” WP members demonstrated several key building blocks for spintronic circuitry made of graphene. Namely, researchers showed that spin current can be efficiently injected into a graphene/hBN heterostructure which supports spin transport even at room temperature. In another paper, researchers presented their finding of a room-temperature field-effect spin transistor in a graphene and MoS2 device. Aside from these imminently practical applications, new research uncovered giant anisotropy in spin lifetimes in layered graphene/TMDC devices, showing the path towards spin filtering. The fact that all these effects were shown at room temperature is promising for real world applications.
All progress of technology based on graphene relies on optimizing the material for different applications and developing scalable synthesis methods. These are two key goals of the “Enabling Materials” WP, which exemplifies its progress through three key publications. The first of these reports on the first ever all-printed, all nanosheet transistors, opening the door to printed electronic devices from layered materials. The second paper demonstrates a scalable, bottom-up method of producing graphene nanoribbons, which transform graphene into a semiconductor by opening a band gap. Transistors made of these ribbons showed excellent switching behavior, promising densely packaged high-performance computing devices. The third report outlines a way to functionalize graphene for applications such as sensors, field-effect transistors, and other electronic devices, by first introducing single-atom defects in a graphene sheet, followed by controlled functionalization.
The “Health and Environment” WP is committed to studying the potential health effects of graphene and related materials (GRMs), both on the researcher and on the user of a graphene-based device. Fortunately, last year’s results show that skin reaction to graphene only occurs at extremely high amounts and exposure levels which are unlikely to occur in regular use. Furthermore, it was shown that graphene oxide (GO) can be rapidly degraded by the human immune system and that biodegradation can be enhanced using specific functional groups.
The “Biomedical Technologies” WP makes use of graphene’s excellent electrical and chemical properties combined with its biocompatibility to study potential use in new biomedical applications. For example, the WP researchers have shown flexible neural implants made of graphene that attach to a rat brain, enabling detection of previously unexplored neural activity. The graphene devices are thin, flexible and have very low noise, able to detect slow-wave activity, epileptic activity, and audio-visual responses. Graphene is also being explored as a novel platform for local delivery of drugs. These devices are now entering the preclinical development stages.
WP “Sensors” covers the broad landscape of sensing, including various kinds of physical and chemical sensors. Last year a prototype “electronic nose” was presented, mimicking the workings of a human nose – an array of sensors that are functionalized for different chemicals. Researchers also took pressure and humidity sensors to new heights, detecting pressure changes down to 25 mbar with suspended graphene membranes and constructing a printed graphene oxide humidity sensor that can be monitored wirelessly. There is close collaboration with industrial partners who have developed multiplexed prototypes for applications such as point-of-care detection of cardiac biomarkers.
The “Electronic Devices” WP targets high frequency and high performance electronic devices enabled by graphene and related materials. Last year was marked by the most complex GRM circuit to date, a processor made of 115 MoS2 transistors. Radio frequency and terahertz applications were also pushed forward, with a demonstrated microwave receiver for signals up to 2.45 GHz, a flexible THz detector, and a demonstration of efficient cooling of graphene-based nanoelectronic devices using hyperbolic phonon cooling.
The “Photonics and Optoelectronics” WP makes use of the exceptional electronic and optical properties of graphene for advances in technology to send and receive optical data signals. A key result last year was the demonstration of a detector with a bandwidth higher than 76 GHz, suitable for data rates of more than 100 Gb/s, produced on a 6” wafer. Graphene light modulators have reached bandwidths of 5 GHz for data transfer rates of 10 Gb/s. Finally, the blending of optics and electronics allowed the construction of a highly sensitive extremely broadband graphene-based camera sensor, covering the ultraviolet, visible and infrared parts of the spectrum.
The WP “Flexible Electronics” addresses the use of GRMs in the rapidly growing flexible electronics industry. To this end, members of the WP produced various electronic devices on flexible substrates using GRMs, such as for example flexible, all-solid-state graphene-based supercapacitors, wearable touch panels, a strain sensor, and a self-powered triboelectric sensor.
The WP “Wafer-Scale System Integration” operates towards integration of graphene technology with silicon-based electronics, a key development that is essential to take advantage of graphene’s potential in electronics. Developing processing methods to this end is the run-of-the-mill of this WP, which intersects with other WPs to yield results in high-speed electronics already mentioned earlier. A strong driving direction for this WP is to evaluate and reduce the costs of making graphene devices.
Energy generation is undoubtedly one of the main research directions of modern technological progress. The WP “Energy Generation” looks into ways that GRMs can be used to improve energy generation, including the improvement of perovskite solar cells (PSCs), highly promising next-generation solar power sources with very high efficiency. Flagship researchers made excellent progress in improving the lifetime and performance of PSCs, while reducing the production cost of PSCs. MoS2 interlayers improved the long-term lifetime of PSCs which retained 80% of their initial efficiency after 568 hours of operation in ambient conditions. Adding a reduced graphene oxide spacer layer to a PSC resulted in low-cost production of PSCs with 20% efficiency, retained up to 95% after 1000h of operation. A pilot production line and a 1 kWp GRM-perovskite solar farm are in the pipeline for the next period.
Once energy is produced, it needs to be reliably stored in batteries with high capacity and long lifetimes. Research in the “Energy Storage” WP tackles this challenge, most notably through the use of graphene in advanced electrodes. Combining graphene and silicon nanoparticles resulted in anodes that maintain 92% of their energy capacity over 300 charge-discharge cycles, with a high maximum capacity of 1500 mAh per gram of silicon. Achieved energy density values are well above 400 Wh/kg. In the next phase, a Spearhead project of the Flagship will focus on pre-industrial production of a silicon-graphene-based lithium ion battery. Furthermore, a spray-coating deposition tool for graphene was developed through this WP, enabling large-scale production of thin films of graphene which were used, for example, to produce supercapacitors with very high power densities.
The WP “Functional Foams and Coatings” works on developing new chemical processing and functionalization methods to enable GRMs at high quality and a large scale. These custom materials span a wide range of uses, including sensors, photocatalysis, anticorrosion, energy applications and more. Aside from a strong streak of high-impact publications, work of last year has resulted in several European and German patents and the creation of a spin-out company of the TU Dresden.
The same wide span of uses goes for the WP “Polymer Composites”, that engineers composites that contain GRMs for multifunctional benefits, including enhanced mechanical strength, thermal and electrical conductivity, and low mass density. The specific focus of this WP is on industries that already make wide-scale use of polymers, such as aerospace, automotive, and energy generation. Aside from fundamental studies of the mechanical impact of embedding graphene with a different aspect ratio, orientation, and the degree of stress transfer between graphene and polymer, WP researchers managed to engineer the load-bearing capability of such composites by optimizing the wrinkling of graphene. Finally, the manufacturing sector will benefit from new discoveries that adding graphene oxide and carbon nanotubes leads to electrically conductive rubbers with enhanced strength, as well as icephobic properties.
Finally, the WP “Production” brings together Europe’s very best manufacturing companies into a value chain to enable large scale manufacturing of GRMs and their end products. The focus of this WP is on optimizing throughput from the other WPs that have a production component to real large-scale industry.
These fantastic achievements are a result of coordinated efforts of the 158 Flagship partners across Europe, however the Flagship continues to include new members through the Associated Members and Partnering Projects modules. Associated Members aid in widening participation and broadening horizons of this unprecedented network of industrial and academic partners.
This year phase Core 1 of the Flagship ends, approaching the half-way point of the ten-year project. The Flagship is now present at major trade shows, such as the Mobile World Congress, Medica, and Composites Europe. Licensing agreements are being signed, products propelled to the marketplace, and spin-offs being launched. Core 2 will see the Flagship organized around six Spearhead projects, with clear objectives designed to fulfill market needs. It is becoming clear that the Graphene Flagship is well on track on its main mission of streamlining the passage of graphene research from the lab floor to end-market products.