PORTLAND, Ore. -- Carbon nanotubes studded with phospholipid disks enable solar cells to perform self-repairing operations similar to plants performing photosynthesis. The resulting photoelectrochemical solar cells are claimed by the Massachusetts Institute of Technology (MIT) researchers to be twice as efficient as the best solid-state solar panels.
The main difference between man-made and natural solar power conversion is that engineers aim to armor solar cells against gradual degradation with solid-state inorganic materials, whereas natural solar conversion uses photosynthesis to anticipate and repair inevitable damage to liquid-state organic materials.
In nature, examples abound of sustainable solar energy usage. For instance, the organic compounds that enable a leaf to perform photosynthesis are regularly damaged by sunlight, but the leaf has self-repair mechanisms. By studying the process by which biological photosynthesis constantly renews its solar-to-fuel transformation machinery, scientists now believe they can create solar cells that mimic that self-repair ability.
MIT researchers are not claiming to have unlocked the secret to photosynthesis, but to have mimicked the self-repairing mechanism used by plants to continually replenish their energy harvesting capabilities.
Photosynthesis includes built-in mechanisms that periodically breaks down a plant's chemical-based engine into basic building blocks, then reassembling a refurbished engine from the renewed components. According to MIT professor Michael Strano, plants perform this function every hour, renewing and recycling their protein-based photosynthesis capabilities to keep them continually working at optimal efficiency.
Strano's formulation mimics the reversibility of photosynthetic processes with synthetic disk molecules called phospholipids, each of which carries its own internal reaction center that coverts light into an electric current. When mixed into a solution with carbon nanotubes, the disks self-assemble around them. Since carbon conducts electricity even better than metals, the nanotubes enhance the transport of electrons freed inside the disks by their exposure to sunlight.
Inside the disks, Strano's team created a photosynthesis-like cyclical mechanism using seven different compounds that self-assemble into harvesters of light. By adding a surfactant, similar to those used to disperse oil in the Gulf this spring, the entire seven-compound assembly can be broken apart into its original components. Then, by forcing the whole solution through a filter that removes the surfactants, the original building blocks again self-assemble into a rebuilt solar cell.
Compared to under 20 percent for the best solid-state solar cells, the liquid-state photoelectrochemical cell achieved 40 percent efficiency; higher concentrations of nanotube-disks could increase efficiency further, according to researchers.
Funding for the research was provided by the MIT Energy Initiative and the U.S. Energy Department.
Taking examples from Nature to come up with technological solutions is as old as Leonardo da Vinci's time and I'm sure earlier examples can be found. Why reinvent the wheel of naural phenomena; just emulate it. Easier said than done. Keen observation can help. Take the MIT work emulating a bird perching and apply the mechanism to a winged aircraft: http://www.nxtbook.com/nxtbooks/cmp/eetimes_milaero_20100830/index.php#/40/OnePage
This is a pioneer research work! As most of the solar cell manufacturers are struggling to achieve 20-25% efficiency with the existing solar cell technologies, a new idea like this one is an essential need to achieve major breakthrough with the efficiency. Again the idea of self-healing technique mimicking the self-repairing mechanism used by plants is also great. Most of the technological breakthroughs (I believe all) are inspired by nature and there is plenty more to learn yet.
Nature has a lot to teach us, but usually we don't listen too closely because our designs are optimized. When evolution makes changes, it usually overlays the new over the old, rather than replace it with an optimized version. The message is that you can't just copy nature, but really need to understand what is going on so that you can mimic the good without copying the unnecessary. That said, I think these researchers are demonstrating that the time it ripe for adding a little complexity to our designs in order to mimic traits like self-healing.
I think you are targeting the heart of the matter in looking for the BOM cost and "true" efficiency (and survivability) of the solution; that indeed will be interesting... but/and as noted by Sanjib below, if 40% efficiency is affordably available it sounds like a real breakthrough.
These researchers claim that by making their solution more concentrated, they can boost efficiency much much further, but this is still lab work. We will have to wait and see what kind of efficiency a commercial version can yield.
Thank you for sharing your thoughts. I agree with what you and Nic_Mokhoff shared about "listening closely" / "keen observation" for applying the learning from the nature. Wish to see this research taking concrete shape in the near future. I was also going though an article on the same topic published in the link below : http://www.msnbc.msn.com/id/39058522/ns/technology_and_science-green_innovation/
The article says (towards the end) that the initial efficiency of this new solar cell is less compared to the current commercial solar panels? How do you interpret that information?
The 40 percent figure was calculated from the chemistry of the reactions, whereas the solution tested was relatively dilute. By improving the chemistry and making the solution more concentrated, they hope to outperform solid-state solar cells.