Due to the damaging impact of UV exposure, a solar cell’s power output can degrade by 20 percent or more over its lifetime.
Researchers at MIT, investigating ways to prevent the power loss over time, are mimicking processes found in nature. In particular, the researchers are looking at the way plants address the problem.
To that point, plants have adopted an interesting strategy. They constantly break down their light-capturing molecules and reassemble them from scratch, so the basic structures that capture the sun’s energy are, for all practical reasons, always brand new.
Imitating that process, the researchers have created a set of self-assembling molecules that can turn sunlight into electricity. The molecules can be repeatedly broken down and then reassembled quickly, just by adding or removing a solution.
This work is being carried out by Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering at MIT, and his team of graduate students and other researchers.
To imitate that process, Strano and his team, supported by grants from the MIT Energy Initiative and the Eni Solar Frontiers Center at MIT, produced synthetic molecules called phospholipids that form disks. These disks provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light. The disks, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes, which are wire-like hollow tubes of carbon atoms that are a few billionths of a meter thick and capable of conducting electricity a thousand times better than copper. The nanotubes hold the phospholipid disks in a uniform alignment so that the reaction centers can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.
The group published a paper on this work in Nature Chemistry last fall.
The bottom line is that the group has demonstrated a way to have certain molecules and other components spontaneously self-assemble into light-harnessing systems.
The challenge is how this dynamically assembled solar cell approach could be used to create a device capable of regenerating itself. To get some insight into the issues of bring this technology forward. The group developed a prototype system. As the solar cell molecules in the prototype became damage, the system’s performance would degrade. Once degradation hit the 25 percent level, a solution is introduced into the system to begin the regeneration process. The damaged molecules are removed, and the remaining components re-assemble into a photoactive material.
Certainly, this work is still in the very early basic research stage. But it demonstrates an approach that might be used in solar cell systems of the future to ensure power degradation over time is reduced. This could potentially change to the cost analysis of building a large-scale solar system. If solar cells could retain their full efficiency over the lifetime of an installation, that would boost the total output a system could deliver over time.
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