New Graphene-Glass Combo Powers “Spontaneous” Solar Cell

February 12th, 2016 by Tina Casey

CleanTechnica has dubbed graphene the “nanomaterial of the new millennium,” partly because this super strong, 2D form of carbon with solar-friendly electronic properties could launch the next generation of high efficiency solar cells. The problem is getting the finicky material to behave, and a team of researchers at Brookhaven National Laboratory is onto an inexpensive, simple way to do that.

Brookhaven Does (Graphene) Windows

Apparently the Brookhaven solution to the graphene problem has been staring everybody in the face, ever since graphene was first discovered in 2004: ordinary window glass.

If you have no windows, then perhaps you have a bottle or two of soda pop or a baking dish. Chances are it’s all the same common soda-lime glass.

Somewhat ironically, according to our friends over at the University of Delaware’s Scientific Glass-Blowing Shop, soda-lime glass is not preferred for delicate research projects:

Soda lime is not as chemical resistant as borosilicate glass. Its lower melting point and higher coefficient or expansion and contraction make it ideal for certain glass to metal operations as well as inexpensive glassware such as pipettes or plate glass. However those same coefficients make it unusable where high heat or great temperature fluctuations are necessary. Because its characteristics it is not recommended that soda lime “apparatus” be purchased in many cases. It is much more difficult (or sometimes impossible) to repair if damaged.

Apparently the Brookhaven team stumbled on to soda-lime glass while exploring a more complex solution, with the poetic explanation in a press release being that “such surprises are part of the beauty of science.”

Graphene Meets Soda-Lime Glass

So, what is it about soda-lime glass that does the trick? The main ingredient, soda (Na2CO3), is a sodium compound, and when you layer graphene onto the glass, the sodium interacts with it. Apparently the interaction naturally results in a doping effect that researchers have been struggling to accomplish, as described by the research team:

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.

Here’s an overhead view of the graphene solar cell, as seen through a scanning electron micrograph (the white scale bar for the micrograph is 10 microns; the inset is a transmission electron micrograph showing the graphene (GR) interface with a scale bar of 100 nanometers):

The new approach solves a conundrum that has bedeviled the application of graphene to solar cells and other electronic devices. In the conventional approach, graphene is “doped” or altered in order to achieve the most efficient electronic balance between it and other materials in the device. However, doping typically involves introducing chemicals, which can cause performance to degrade over time.

The Brookhaven team was heading down the doping track when it had its eureka moment. The team was tinkering around with a new system composed of a graphene solar cell stacked on a conventional high-performance semiconductor (CIGS, for those of you keeping score at home), all on top of a piece of soda-lime glass:

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.

In other words, the graphene and CIGS layers were spontaneously compatible without the need for any further alteration.

The rest was a matter of detective work. The team knew what they observed, they just didn’t know why it was happening until they probed around and discovered that sodium in the glass was acting as a built-in doping agent.

If you’re feeling ambitious, you can check out the full study in the journal Scientific Reports under the title “Spontaneous and strong multi-layer graphene n-doping on soda-lime glass and its application in graphene-semiconductor junctions.“

So far the team has shepherded its graphene solar cell to the proof of concept stage. They’ve also demonstrated that the effect persists over a period of several weeks when the device is exposed to air — a critical issue for solar cell application.

It’s A Glass-Graphene World, We Just Live In It

Next steps include formulating a processes to fine-tune the new doping technique and conducting more intensive real-world strength tests.

There’s still a long way to go, but the team is already looking forward to the day when their glass-graphene system replaces, well, everything:

…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.

So…we were just talking about how the solar powered car of the future is practically here already. If the Brookhaven research pans out, perhaps we’ll all be driving around with solar moon roofs over our heads.

That would go nicely with the graphene-enabled fuel cell supercar that our sister site Gas2.org has been following, so stay tuned.

Images (screenshots): via Brookhaven National Laboratory.









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