MMaterialsgateNEWS 2016/02/15

Related MaterialsgateCARDS

Graphene leans on glass to advance electronics

Scientists' use of common glass to optimize graphene's electronic properties could improve technologies from flat screens to solar cells

Graphene, the two-dimensional powerhouse, packs extreme durability, electrical conductivity, and transparency into a one-atom-thick sheet of carbon. Despite being heralded as a breakthrough "wonder material," graphene has been slow to leap into commercial and industrial products and processes.

Now, scientists have developed a simple and powerful method for creating resilient, customized, and high-performing graphene: layering it on top of common glass. This scalable and inexpensive process helps pave the way for a new class of microelectronic and optoelectronic devices--everything from efficient solar cells to touch screens.

The collaboration--led by scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, Stony Brook University (SBU), and the Colleges of Nanoscale Science and Engineering at SUNY Polytechnic Institute--published their results February 12, 2016, in the journal Scientific Reports.

"We believe that this work could significantly advance the development of truly scalable graphene technologies," said study coauthor Matthew Eisaman, a physicist at Brookhaven Lab and professor at SBU.

The scientists built the proof-of-concept graphene devices on substrates made of soda-lime glass--the most common glass found in windows, bottles, and many other products. In an unexpected twist, the sodium atoms in the glass had a powerful effect on the electronic properties of the graphene.

"The sodium inside the soda-lime glass creates high electron density in the graphene, which is essential to many processes and has been challenging to achieve," said coauthor Nanditha Dissanayake of Voxtel, Inc., but formerly of Brookhaven Lab. "We actually discovered this efficient and robust solution during the pursuit of something a bit more complex. Such surprises are part of the beauty of science."

Crucially, the effect remained strong even when the devices were exposed to air for several weeks--a clear improvement over competing techniques.

The experimental work was done primarily at Brookhaven's Sustainable Energy Technologies Department and the Center for Functional Nanomaterials (CFN), which is a DOE Office of Science User Facility.

The graphene tweaks in question revolve around a process called doping, where the electronic properties are optimized for use in devices. This adjustment involves increasing either the number of electrons or the electron-free "holes" in a material to strike the perfect balance for different applications. For successful real-world devices, it is also very important that the local number of electrons transferred to the graphene does not degrade over time.

"The graphene doping process typically involves the introduction of external chemicals, which not only increases complexity, but it can also make the material more vulnerable to degradation," Eisaman said. "Fortunately, we found a shortcut that overcame those obstacles."

The team initially set out to optimize a solar cell containing graphene stacked on a high-performance copper indium gallium diselenide (CIGS) semiconductor, which in turn was stacked on an industrial soda-lime glass substrate.

The scientists then conducted preliminary tests of the novel system to provide a baseline for testing the effects of subsequent doping. But these tests exposed something strange: the graphene was already optimally doped without the introduction of any additional chemicals.

"To our surprise, the graphene and CIGS layers already formed a good solar cell junction!" Dissanayake said. "After much investigation, and the later isolation of graphene on the glass, we discovered that the sodium in the substrate automatically created high electron density within our multi-layered graphene."

Pinpointing the mechanism by which sodium acts as a dopant involved a painstaking exploration of the system and its performance under different conditions, including making devices and measuring the doping strength on a wide range of substrates, both with and without sodium.

"Developing and characterizing the devices required complex nanofabrication, delicate transfer of the atomically thin graphene onto rough substrates, detailed structural and electro-optical characterization, and also the ability to grow the CIGS semiconductor," Dissanayake said. "Fortunately, we had both the expertise and state-of-the-art instrumentation on hand to meet all those challenges, as well as generous funding."

The bulk of the experimental work was conducted at Brookhaven Lab using techniques developed in-house, including advanced lithography. For the high-resolution electron microscopy measurements, CFN staff scientists and study coauthors Kim Kisslinger and Lihua Zhang lent their expertise. Coauthors Harry Efstathiadis and Daniel Dwyer--both at the College of Nanoscale Science and Engineering at SUNY Polytechnic Institute--led the effort to grow and characterize the high-quality CIGS films.

"Now that we have demonstrated the basic concept, we want to focus next on demonstrating fine control over the doping strength and spatial patterning," Eisaman said.

The scientists now need to probe more deeply into the fundamentals of the doping mechanism and more carefully study material's resilience during exposure to real-world operating conditions. The initial results, however, suggest that the glass-graphene method is much more resistant to degradation than many other doping techniques.

"The potential applications for graphene touch many parts of everyone's daily life, from consumer electronics to energy technologies," Eisaman said. "It's too early to tell exactly what impact our results will have, but this is an important step toward possibly making some of these applications truly affordable and scalable."

For example, graphene's high conductivity and transparency make it a very promising candidate as a transparent, conductive electrode to replace the relatively brittle and expensive indium tin oxide (ITO) in applications such as solar cells, organic light emitting diodes (OLEDs), flat panel displays, and touch screens. In order to replace ITO, scalable and low-cost methods must be developed to control graphene's resistance to the flow of electrical current by controlling the doping strength. This new glass-graphene system could rise to that challenge, the researchers say.

Source: DOE/Brookhaven National Laboratory – 12.02.2016.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

Rice researchers say material is more or less brittle, depending on how hard it's pulled

The same slip-and-stick mechanism that leads to earthquakes is at work on the molecular level in nanoscale materials, where it determines the shear plasticity of the materials, according to scientists at Rice University and the State University of Campinas, Brazil. The Rice lab of materials scientist Pulickel Ajayan found that random molecules scattered within layers of otherwise pristine graphene affect how the layers interact with each other under strain. Plasticity is the ability of a material to permanently deform when strained. The Rice researchers, thinking about future things like flexible electronics, decided to see how graphene oxide "paper" would handle shear strain... more read more

An international team of researchers, led by Penn State, has developed ultrasensitive gas sensors based on the infusion of boron atoms into the tightly bound matrix of carbon atoms known as graphene.

The group is composed of researchers from six countries and includes the 2010 Noble laureate and graphene pioneer Konstantin Novoselov, and Morinobu Endo, the discoverer of carbon nanotubes. Graphene is well known for its remarkable strength and ability to transport electrons at high speed, but it is also a highly sensitive gas sensor. By adding boron atoms, the boron graphene (BG) sensors were able to detect noxious gas molecules at extremely low concentrations, parts per billion in the case of nitrogen oxides and parts per million for ammonia, the two gases tested to date. This translates to a 27 times greater sensitivity to NOx and a 105 times greater sensitivity to ammonia compared to... more read more

Scientists in Korea have developed wearable, graphene-coated fabrics that can detect dangerous gases present in the air, alerting the wearer by turning on an LED light.

The researchers, from the Electronics and Telecommunications Research Institute and Konkuk University in the Republic of Korea, coated cotton and polyester yarn with a nanoglue called bovine serum albumin (BSA). The yarns were then wrapped in graphene oxide sheets. Graphene is an incredibly strong one-atom-thick layer of carbon, and is known for its excellent conductive properties of heat and electricity. The graphene sheets stuck very well to the nanoglue—so much so that further testing showed the fabrics retained their electrical conducting properties after 1,000 consecutive cycles of bending and straightening and ten washing tests with various chemical detergents. Finally, the graphene... more read more

Graphene has been called a wonder material, capable of performing great and unusual material acrobatics. Boron nitride nanotubes are no slackers in the materials realm either, and can be engineered for physical and biological applications.

However, on their own, these materials are terrible for use in the electronics world. As a conductor, graphene lets electrons zip too fast--there's no controlling or stopping them--while boron nitride nanotubes are so insulating that electrons are rebuffed like an overeager dog hitting the patio door. But together, these two materials make a workable digital switch, which is the basis for controlling electrons in computers, phones, medical equipment and other electronics. Yoke Khin Yap, a professor of physics at Michigan Technological University, has worked with a research team that created these digital switches by combining graphene and boron nitride nanotubes. The journal Scientific... more read more

MaterialsgateNEWSLETTER

Partner of the Week

Search in MaterialsgateNEWS

Books and products

MaterialsgateFAIR:
LET YOURSELF BE INSPIRED