Scientists at the Massachusetts Institute of Technology (MIT) have a created a set of self-assembling molecules that can turn sunlight into power, and which can repeatedly be broken down and reassembled by adding or removing solution. The scientific breakthrough—inspired by a natural process used by plants to renew light-capturing molecules that have been degraded by the sun—could mean that researchers are closer to creating a self-healing photovoltaic (PV) technology that can keep repairing itself to avoid loss in performance.

MIT Associate Professor of Chemical Engineering Michael Strano, who is conducting the research with a team of graduate students, said the research is important because developers of novel systems for generating electricity from light don’t often study how the systems change over time. For conventional silicon-based PV cells, there is little degradation, but with many new systems being developed—either for lower cost, higher efficiency, flexibility, or other improved characteristics—the degradation can be very significant. “Often people see, over 60 hours, the efficiency falling to 10 percent of what you initially saw,” he said.

Strano said the idea to create a self-assembling PV cell occurred to him while contemplating how “a leaf on a tree is recycling its proteins about every 45 minutes, even though you might think of it as a static photocell.”

To imitate that process, the MIT team produced a system of synthetic molecules composed of seven different compounds, including carbon nanotubes, phospholipids, and proteins that make up the reaction centers, which under the right conditions spontaneously assemble themselves into a light-harvesting structure that produces an electric current (Figure 4). When a surfactant is added to the mix, the seven components all come apart and form a soupy solution. Then, when the researchers removed the surfactant by pushing the solution through a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell.

4. In good repair. MIT researchers have produced a set of synthetic molecules that mimic the ability of plants to recycle light-capturing components that have been degraded by the sun. The breakthrough could mean that researchers are closer to creating a self-assembling photovoltaic technology that can keep repairing itself to avoid loss in performance. This proof-of-concept version of the researchers’ photoelectrochemical cell was used for laboratory tests. Courtesy: MIT/ Patrick Gillooly

The team built a prototype cell to test it out and ran it through repeated cycles of assembly and disassembly over a 14-hour period with no loss of efficiency. The individual reactions of these new molecular structures in converting sunlight are about 40% efficient—“about double the efficiency of today’s best solar cells,” MIT claimed. But in the initial work, the concentration of the structures in the solution was low, so the overall efficiency of the device—the amount of electricity produced for a given surface area—was very low. The researchers are now working to find ways to greatly increase the concentration.

—Sonal Patel is POWER’s senior writer.