It’s not a joke, MIT’s Miles C. Barr, Jill A. Rowehl, Richard R. Lunt, Jingjing Xu, Annie Wang, Christopher M. Boyce, Sung Gap Im, and Vladimir Bulovi? led by Karen K. Gleason are printing photovoltaic cells on regular paper. Moreover, the process as being reported in MIT News, its possible to print on ordinary untreated paper, cloth or plastic as the substrate for building a solar cell array.
The new technology paper is published in the journal Advanced Materials, published online July 8.
The MIT News article opens describing that the sheet of paper looks like any other document that might have just come spitting out of an office printer, with an array of colored rectangles printed over much of its surface. But then a researcher picks it up, clips a couple of wires to one end, and shines a light on the paper. Instantly an LCD clock display at the other end of the wires starts to display the time. Seems to work, and considering the skill sets and innovative atmosphere at MIT its not a great surprise so much as a quite pleasant one. Photovoltaic is still far too expensive for mass adoption, and in the current economy and government situations, PV is a technology that must self wean itself from incentives.
The device is tough, formed from special “inks” deposited on the paper. It can be folded up to slip into a pocket, then unfolded to watch it again generating electricity in the sunlight. It’s a more complex than just printing out a paper. In order to create an array of photovoltaic cells on the paper, five layers of material need to be deposited onto the same sheet of paper in successive passes, using a mask (also made of paper) to form the patterns of cells on the surface. And the process has to take place in a vacuum chamber.
Solar Cells Printed on Paper. Graduate student Miles Barr holds a sheet of paper that has had one of the layers of the solar cell printed on its surface. Image Credit: Patrick Gillooly.
But the basic process is essentially the same as the one used to make the silvery lining in your bag of potato chips: a vapor-deposition process that can be carried out inexpensively on a vast commercial scale. When one considers the total area of metalized bags like potato chips versus photovoltaic panels the idea of the scale becomes clearer.
The MIT production process technique represents a major departure from today’s systems creating most solar cells on heavy solid inflexible substrates encased in glass, that require exposing the substrates to potentially damaging conditions, either in the form of liquids or high temperatures to etch the silicon into the needed shapes.
The new printing process uses vapors, not liquids, and temperatures less than 120 degrees Celsius. While the PC printer metaphor is used, the MIT News article clarifies that masks are used and vapor deposition takes place over five steps. Its not really so much inkjet printing as five round trips through the potato chip bag process making it more complex but still quite simple, low energy and material intensive and astonishingly low cost.
Using thin film PET plastic in lieu of paper as the substrate in printing a solar cell, the now flexible resilient solar cells still functions even when folded up into a paper airplane. Such assaults of folding and unfolding it 1,000 times, yields no significant loss of performance.
The team is hard at getting past function to appreciable efficiencies. Presently the paper-printed solar cells have an efficiency of about 1 percent, but the team believes this can be increased significantly with further fine-tuning of the materials.
Karen Gleason, who is the Alexander and I. Michael Kasser Professor of Chemical Engineering at MIT points out, “Often people talk about deposition on a flexible device — but then they don’t flex it, to actually demonstrate” that it can survive the stress. Beyond folding the MIT team has tried other tests of the device’s robustness. For example, Gleason explains, they took a finished paper solar cell and ran it through a laser printer, printing on top of the photovoltaic surface. That subjects the cell to the high temperature of the toner-fusing step, and demonstrated that it still worked. Test cells the group produced last year still work, demonstrating their long shelf life.
These attributes put a whole new perspective on the photovoltaic cell. Professor of Electrical Engineering Vladimir Bulovi? brings the idea forward. Because of the low weight of the paper or plastic substrate compared to conventional glass or other materials, “We think we can fabricate scalable solar cells that can reach record-high watts-per-kilogram performance. For solar cells with such properties, a number of technological applications open up,” he says. For example, in remote developing-world locations, weight makes a big difference in how many cells could be delivered in a given load.
That’s a major change in perspective.
The MIT team has demonstrated that the paper could be coated with standard lamination materials, to protect it from the elements opening up outdoor use. Plastic laminations aren’t going to last like glass, but say at 7% of the energy production at perhaps 1/1000th the cost of current glass photovoltaic cells, life expectancy isn’t going to have such an important factor in calculations.
“Printing” cells is commercial now at a price advantage to silicon on glass. Research has been working to produce solar cells and other electronic components on paper, but the big stumbling block has been paper’s rough, fibrous surface at a microscopic scale. To counter that, past attempts have relied on coating the paper first with some smooth material. The MIT team uses ordinary, uncoated paper, including printer paper, tissue, tracing paper and even newsprint with the printing still on it. All of these worked just fine. It’s a robust technology.
The MIT work in the early stages will most likely go to applications of shorter life times.
Wall applications, portable devices, and disposable electronics come to mind. As more research covers the problems of environmental exposure, raising the efficiency, optimizing connections and the field of applications will expand. Perhaps someone will
tie the ideas of gathering more of the spectrum together and very low cost photovoltaic solar will become a consumer reality.
It’s getting so a skeptic can look forward to photovoltaic solar in the coming years.
By. Brian Westenhaus
Source: Solar Cells Printed on Paper