Jul
15
New Solar Cell Design Is Much More Efficient
July 15, 2015 | Leave a Comment
The team found that by assembling the components of the panels to more closely resemble the natural systems plants use to tap the sun’s energy, it may be possible to separate positive and negative charges in a stable way for up to several weeks compared to just millionths of a second – the current standard for many modern solar panels.
Sarah Tolbert, a UCLA professor of chemistry and one of the senior authors of the research explained the background with, “In photosynthesis, plants that are exposed to sunlight use carefully organized nanoscale structures within their cells to rapidly separate charges – pulling electrons away from the positively charged molecule that is left behind, and keeping positive and negative charges separated. That separation is the key to making the process so efficient.”
Buckyball and Polymer Solar Cell Construction. UCLA Scientists have devised a new arrangement of solar cell ingredients, with bundles of polymer charge donors (green rods) and neatly organized spherical carbon molecules, also known as fullerenes or buckyballs, serving as charge acceptors (purple, red). The researchers studied the new design at SLAC’s Stanford Synchrotron Radiation Lightsource. Image Credit: UCLA. Click image for the largest view.
The team’s X-ray studies at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), a DOE Office of Science User Facility, enabled them to see, at a microscopic level, which material design has the most ideal structure at the nanoscale for promoting this charge separation.
The team’s study results have been published in the journal Science.
To capture energy from sunlight, conventional rooftop solar cells use silicon, which can be expensive. Solar cells can also be made using lower-cost materials like plastics, but plastic cells are far less efficient – in large part because the separated positive and negative charges in the material often recombine before they can become electrical energy.
Tolbert continued, “Modern plastic solar cells don’t have well-defined structures like plants do because we never knew how to make them before. But this new system pulls charges apart and keeps them separated for days, or even weeks. Once you make the right structure, you can vastly improve the retention of energy.”
The UCLA-developed system is composed of strands of a polymer, the building block of plastics, that absorb sunlight and pass electrons to a fullerene, a spherical carbon molecule also known as a “buckyball.”
The materials in these types of solar cells are typically organized like a plate of cooked pasta – a disorganized mass of long, skinny polymer “spaghetti” with random fullerene “meatballs.” But this arrangement makes it difficult to get current out of the cell because the electrons sometimes hop back to the polymer spaghetti and are lost.
The researchers figured out how to arrange the elements more neatly – small bundles of uncooked spaghetti with precisely placed meatballs. Some fullerene meatballs are designed to sit inside the polymer spaghetti bundles and others are forced to stay on the outside.
The fullerenes inside the structure take electrons from the polymers and toss them to the outside fullerenes, which can effectively keep the electrons separated from the polymer for weeks. A series of experiments at SSRL and other studies confirmed the best arrangement of the polymer strands and buckyballs.
Benjamin Schwartz, a UCLA professor of chemistry and a co-author of the study explained what happens, “When the charges never come back together, it becomes easier to get them out of the solar cell in the form of electricity. This is the first time such long charge lifetimes have been shown using this type of material.”
Researchers found that the materials self-assemble into this ordered form when placed in close proximity. The new design is also more environmentally friendly than current technology, because the materials can assemble in water instead of more toxic organic solutions that are typically used.
“Once you make the materials, you can dump them into water and they assemble into the appropriate structure because of the way the materials are designed,” Schwartz said.
The UCLA researchers are now working on how to incorporate the technology into actual solar cells, and Tolbert said the team is planning follow-up research at SSRL.
Looks like quite an improvement, if there is some way to come up with the buckyball fullerenes at low cost, an idea that others are working on as market potentials are appearing quite frequently.
No word on actual efficiencies yet, this is basic research, but a big part of the allure is the ability to hang on to the electrons without them slipping away – offering a major change in what solar efficiency will mean in the years to come.
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