We've told you how carbon nanotubes are being used for some amazing things, like the basis of a wearable energy-harvesting fabric, and reinforcing carbon fiber composite to make it seaworthy for duty as a boat construction material. Now, in a major first, researchers at Stanford University have built a prototype of an all-carbon solar cell, including carbon nanotubes.
Why carbon? Because it's a lot cheaper than silicon, and it's also abundant and highly conductive.
Carbon has the potential to produce high performance for its low cost, said Stanford Professor of Chemical Engineering, and the study's senior author, Zhenan Bao, in a university news article. "Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties."
The study builds on previous work done in her research group's lab. The results were published in an article in ACS Nano (subscription or purchase only).
Researchers at Stanford University have built a prototype of an all-carbon solar cell that includes carbon nanotubes in both the photoactive layer and the electrodes. (Source: Mark Shwartz / Stanford University)
The prototype is a flexible, thin-film solar cell made of carbon that is coated from solution. In most thin-film solar cells, the electrodes are made of conductive metals, such as silver and indium tin oxide. But as demand for indium rises, it's becoming scarce and more expensive, compared to carbon.
The new carbon-based cell consists of a photoactive layer made of carbon nanotubes and 1-nm-wide carbon buckyballs, sandwiched between two electrodes. The electrodes are made of single-walled carbon nanotubes and graphene.
The technique used for coating the cell can further reduce manufacturing costs, since compared to processing silicon, the team's coating methods reduce process steps and don't require expensive tools and manufacturing equipment, said Stanford graduate student Michael Vosgueritchian, co-lead author of the study. Potential applications could be coating windows, cars, or the surfaces of buildings to capture solar energy and generate electricity.
Because carbon withstands extreme environments much better than silicon, these cells might also be used in high temperature, high stress applications where silicon can't function.
"To the best of our knowledge, this is the first demonstration of a working solar cell that has all of the components made of carbon," said Bao. Although other researchers have reported the production of an all-carbon solar cell, those prototypes' carbon included only the inside photoactive layer, and not the electrodes.
Although carbon is plentiful and highly conductive, it's not known for being a good semiconductor, and is therefore very inefficient, since it absorbs near-infrared (NIR) light wavelengths. However, single-walled carbon nanotubes have superior electrical and mechanical properties, and many of them are semiconducting. They can also be easily dispersed in organic solvents or water, making them compatible with high-volume, low-cost coating processes such as large area roll-to-roll.
The research team is examining different methods for improving efficiency. One way is to improve the smoothness of each layer by improving layer-stacking methods, so they can collect more current. Other carbon nanomaterials that absorb more light across a wider spectrum are also being considered.
Other members of the research team included co-lead author of the study, postdoctoral Stanford researcher Marc Ramuz; postdoctoral Stanford researcher Peng Wei; and Chenggong Wang and Yongli Gao of the University of Rochester's Department of Physics and Astronomy.
Silicon may be cheap as a raw material, but not so much when it's processed to make wafers, in this case, solar wafers and cells. On the one hand, the solar industry began by leveraging the huge existing infrastructure for manufacturing silicon wafers, assuming this would be the fastest way to getting costs down. That was a reasonable assumption at the time, but the reality has proven to be a bit more complex. As the article states, silicon processing steps can be many and they're not cheap. Thin-film is not a monolithic manufacturing method. The cost of thin-film to make solar cells is highly variable, and depends on many factors, including base materials, coating methods, and the coating itself. But this particular method does away with wafers altogether, which is a major potential of thin-film, and the material's potential means better conductivity and light absorption for low cost.
The photoabsorber is a diminishing part of the cost of a solar module and efficiency is it's salient attribute. As for abundance, silica is 60% of the continental crust - it's literally everywhere, even if you restrict yourself to clean beach sand. And, it's literally dirt cheap. The cost in a photoabsorber material is in the processing of it not the raw material.
The transparent conductor in most production thin film panels is tin oxide (not ITO) where tin oxide coated glass is a commodity in the glazing industry i.e. not specific to solar modules and therefore cost optimized. The next alternatives are various zinc oxide alloys.
The back contact/mirror in production modules is generally not silver although, even when it is, it is a very thin coat. More commonly it is a nickel or aluminum alloy.
Keep in mind that the primary value proposition of thin film is low cost offsetting low efficiency. The problem for thin film is that the cost of solar grade silicon has plumeted (~10X since I started with solar), the utilization of silicon (grams per Watt) has been reduced (~3X) and efficiency has increased (~50%). Over my brief history, the cost of silicon photoabsorer in $/W terms has gone down ~45X. Another advantage of silicon is that 25+ year operating lifetimes have been demonstrated.
It's easy to forget that any technology requires an entire ecosystem to support it - that's why it takes so long for it to emerge as a commercial product if ever. The first semiconductor solar cell was demonstrated in 1888, the first silicon cel in 1954 and yet silicon solar cells are still not a mature technology.
Don't rain on their parade! They acknowledge that efficiency is being worked on, and one would expect it to be low at this point. This is something others have been chasing for decades with other solar cell materials too, which had horrible efficiency at first. (Or still does.) But say this costs half as much, but has half the energy efficiency. A net zero, disregarding real estate required. And if you can put it on the glass of a office tower which is already a net waste of energy, awesome.
I get excited at every article like this, whether it's batteries, solar, wind, wave, etc. I'm hoping for those big breakthroughs, i.e. game-changing scientific and engineering accomplishments that will go a long way to eliminating fossil fuels. That carbon was sequestered for eons, and we are freeing it without much regard for future effects.
GeorgeG, 'photoabsorbers' is a new term for me, and I found nothing on a Google search page.
Full disclosure- I have a lovely FL home which at high tide, is just a few feet above sea level!
Exactly: efficiency is king - especially now as the cost of photoabsorbers is becoming a fraction of the cost of a solar module. For an emerging technology, the first number to look at is the theoretical efficiency with the guesstimate that ultimately volume production product will achieve approximately 80% of that.
The researchers omitted one fact - efficiency. I couldn't find anything about the efficiency of their way-way cool carbon solar cell compared to standard silicon solar cells in the linked article.
Inspired by the hooks a parasitic worm uses to penetrate its host's intestines, the Karp Lab has invented a flexible adhesive patch covered with microneedles that adheres well to wet, soft tissues, but doesn't cause damage when removed.
Engineers at the University of California, San Diego are designing a robotic arm that takes inspiration from the loose, flexible, yet very strong structure of the armored plates on a seahorse's tail.
Researchers at the Missouri University of Science & Technology have designed a new nanoscale material that can transmit light faster than the 186,000 miles per second it usually takes to travel through air.
It has often been said that as California goes, so goes the nation. This spring, the state's wind power is setting energy generation records and solar energy generation is expected to rise sharply during the second half of 2013.
The latest model of Liquid Robotics' Wave Glider autonomous, unmanned marine vehicle (UMV), the SV3, is reportedly the world's first hybrid wave- and solar-power-propelled unmanned ocean robot.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
7 
