A flexible and foldable array of solar cells has been printed on a sheet of paper. (MIT/Patrick Gillooly)
New MIT-developed materials make it possible to produce photovoltaic cells on paper or fabric. The technique represents a major departure from the systems used until now to create most solar cells, which require exposing the substrates to potentially damaging conditions, either in the form of liquids or high temperatures.

The new printing process uses vapors, not liquids, and temperatures less than 120 degrees Celsius. These “gentle” conditions make it possible to use ordinary untreated paper, cloth, or plastic as the substrate on which the solar cells can be printed.

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. The process has to take place in a vacuum chamber.

The MIT researchers describe printing a solar cell on a sheet of PET plastic (a thinner version of the material used for soda bottles) and then folding and unfolding it 1,000 times, with no significant loss of performance. By contrast, a commercially produced solar cell on the same material failed after a single folding.

“We have demonstrated quite thoroughly the robustness of this technology,” says Vladimir Bulović, professor of electrical engineering. In addition, 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.

In the video below, a paper solar cell circuit is dynamically folded and unfolded while the voltage is simultaneously measured on the meter. The paper photovoltaic is illuminated from below with simulated solar illumination.

(MIT)