Want to take a solar cell to a remote location so you can easily charge your flashlight or your cell phone? No problem: fold it up and slip it into your back pocket.
That’s the promise of a new technology developed by MIT professors Karen Gleason ‘82, SM ‘82, and Vladimir Bulovi, working with graduate student Miles Barr and several other students and postdocs. They have developed a way to print a solar cell onto almost any material, including flexible plastics, cloth, and paper. In tests, the new photovoltaic material showed virtually no loss of performance after being folded and unfolded 1,000 times.
In the United States, a solar cell’s supporting structure, the installation process, and the substrate (usually glass) that holds the photovoltaic material can cost up to twice as much as the active components of the cell itself. Printing solar cells directly onto inexpensive materials and then just fastening them to a wall for support could drastically reduce the costs of solar installations, which could be incorporated into window shades or wallpaper. Today, most commercial photovoltaic cells are produced using very high temperatures. The printing process developed by the MIT team requires temperatures of less than 120 °C, making it possible to use untreated cloth, plastic, or even ordinary paper as a substrate. The process also has an advantage over recently developed methods that print solar cells by using liquids to deposit organic materials onto a substrate. While printing with liquids can leave gaps on rough surfaces, hindering the device’s electrical conductivity, Gleason and Bulovi’s process uses vapors instead of liquids, producing a more uniform layer, even on rough surfaces like paper. And paper costs a thousandth as much as glass for a given area, the researchers say.
Because paper and plastic are so much lighter than glass or other substrate materials, Bulovi says, “we think we can fabricate scalable solar cells that can reach record-high watts-per-kilogram performance.”
To create an array of photovoltaic cells using the new method, five successive layers of material are deposited onto a sheet of paper (or cloth or plastic) in a vacuum chamber; stencil-like masks are used to form the necessary patterns. The vapor deposition process, similar to that used to make the silvery lining in potato chip bags, is quite adaptable to large-scale manufacturing.
The paper-printed solar cells currently turn just 1 percent of incoming sunlight into electricity, but the researchers believe their efficiency can be increased significantly by fine-tuning the materials. Even at the present level, Bulovi says, the cells are “good enough to power a small electric gizmo.”