A collaborative team of scientists from 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 have developed a simple method for creating resilient, customized, and high-performing graphene: layering it on top of common glass. The scalable and inexpensive process may help pave the way for a new class of microelectronic and optoelectronic devices-from efficient solar cells to touch screens.
The team designed 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. Unexpectedly, the sodium atoms in the glass had a powerful effect on the electronic properties of the graphene - it created high electron density in the graphene, which is essential to many processes and has been challenging to achieve. Also, the effect remained strong even when the devices were exposed to air for several weeks- a clear improvement over competing techniques.
The process in question revolves 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 reach 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. But graphene doping processes usually include the introduction of external chemicals, which not only increases complexity, but can also make the material more vulnerable to degradation. This new process, however, is a shortcut of sorts that overcomes these 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 odd: the graphene was already optimally doped without the introduction of any additional chemicals. After much investigation, and the later isolation of graphene on the glass, they discovered that the sodium in the substrate automatically created high electron density within the multi-layered graphene.
Now that the basic concept has been demonstrated, the scientists want to focus on achieving fine control over the doping strength and spatial patterning. They now need to look 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.