Four-junction, four-terminal stacked solar cell hits 43.9 percent efficiency

Four-junction, four-terminal stacked solar cell hits 43.9 percent efficiency

By Darren Quick
April 30, 2014

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Arrays of stacked multi-junction cells achieving ultra high efficiencies were produced using a printing-based assembly process
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The ultimate goal of solar cell technology is to be able to generate electricity at costs lower than sources such as coal, natural gas and nuclear. Key to this is continuing improvements in conversion efficiency, and with the development of the first four-junction, four-terminal stacked solar cell produced using a micro transfer printing process, researchers have taken another step towards this goal by achieving efficiencies of up to 43.9 percent, with the possibility of exceeding 50 percent in the near future.
The multilayer, microscale solar cell was created by North Carolina-based Semprius Inc. and California-based Solar Junction, working in collaboration with a team from the University of Illinois at Urbana-Champaign led by Professor John Rogers. Using Semprius' proprietary high-speed micro transfer printing process high that it says is able to simultaneously produce thousands of stacked microcells with very high yields, the team stacked a triple-junction microcell on top of a single-junction microcell to create a four-junction, four-terminal stacked solar cell.
The team says the use of four junctions allows the stacked cell to capture a broader range of the solar spectrum, while the use of four terminals rather than the standard two increases the yield of the solar cell under normal operation in the field. Additionally, a new interfacial material that is placed between the top and bottom cells helps to optimize overall efficiency by minimizing optical losses within the stack.

The triple-junction solar cell is covered in an anti-reflective coating to ensure efficient transmission of light to the uppermost layers, while the bottom cell is a single-junction germanium microcell. Light with wavelengths between 300 and 1,300 nm is captured by the triple-junction cell, while light with wavelengths from 1,300 to 1,700 nm passes through to the germanium cell. The result is a multilayer, microscale solar cell that the team says outperforms conventional silicon and single-junction solar cell in terms of efficiency.
"The strategy involves high-speed, printing-based manipulation of thin, microscale solar cells and new interface materials to bond them into multilayer stacks,” Rogers said. "Quadruple-junction, four-terminal solar cells that we can build in this way have individually measured efficiencies of 43.9 percent."
However, Semprius, which was co-founded by Rogers in 2006 to commercialize ultrahigh efficiency photovoltaic modules, promises that the same process will be capable of achieving efficiencies exceeding 50 percent in the near future.
Like the 44.4 percent efficiency record reported by Sharp last year, the 43.9 percent efficiency figure was achieved using a lens system to concentrate light onto the solar cells. Using a dual-stage optics system, the incident sunlight was focused more than 1,000 times. Modules created from the microscale solar cells also achieved efficiencies of 36.5 percent under the same conditions.
"This is very nice work," stated Ali Javey, a professor of electrical engineering and computer sciences at the University of California, Berkeley, who wasn't involved in the research. "The results are impressive, and the schemes appear to provide a route to ultra-high efficiency photovoltaics, with strong potential for utility-scale power generation."
Rogers is first author of a paper detailing the new solar cell that is published this week in the journal Nature Materials.
Sources: Semprius, University of Illinois at Urbana-Champaign

http://www.gizmag.com/four-junction-four-terminal-stacked-solar-cell/31868/

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Scientists Discover How to Generate Solar Power in the Dark

Meet 'photoswitches,' a breakthrough set of materials that act as their own batteries, absorbing energy and releasing it on demand.

Todd Woody Apr 15 2014, 1:27 PM ET

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The next big thing in solar energy could be microscopic.
Scientists at MIT and Harvard University have devised a way to store solar energy in molecules that can then be tapped to heat homes, water or used for cooking.

The best part: The molecules can store the heat forever and be endlessly re-used while emitting absolutely no greenhouse gases.  Scientists remain a way’s off in building this perpetual heat machine but they have succeeded in the laboratory at demonstrating the viability of the phenomenon called photoswitching.

An Atlantic Special Report
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“Some molecules, known as photoswitches, can assume either of two different shapes, as if they had a hinge in the middle,” MIT researchers said in statement about the paper published in the journal Nature Chemistry. “Exposing them to sunlight causes them to absorb energy and jump from one configuration to the other, which is then stable for long periods of time.”

To liberate that energy all you have to do is expose the molecules to a small amount of light, heat or electricity and when they switch back to the other shape the emit heat. “In effect, they behave as rechargeable thermal batteries: taking in energy from the sun, storing it indefinitely, and then releasing it on demand,” the scientists said.

The researchers used a photoswitching substance called an azobenzene, attaching the molecules to substrates of carbon nanotubes. The challenge: Packing the molecules closely enough together to achieve a sufficient energy density to generate usable heat.

It appeared that the researchers had failed when they were only able to pack fewer than half the number of molecules needed as indicated by an earlier computer simulation of the experiment.

But instead of hitting a projected 30 percent increase in energy density, they saw a 200 percent increase. It turned out that the key was not so much packing azobenzene molecules tightly on individual carbon nanotubes as packing the nanotubes close together. That’s because the azobenzene molecules formed “teeth” on the carbon nanotubes, which interlocked with teeth on adjacent nanotubes. The result was the mass needed for a usable amount of energy storage.

That means different combinations of photoswitching molecules and substrates might achieve the same or greater energy storage, according to the researchers.

So how would molecular solar storage work if the technology can be commercialized? Timothy Kucharski, the paper’s lead author and a postdoc at MIT and Harvard, told The Atlantic that most likely the storage would take a liquid form, which would be easy to transport.

“It would also enable charging by flowing the material from a storage tank through a window or clear tube exposed to the sun and then to another storage tank, where the material would remain until it's needed,” Kucharski said in an email.  “That way one could stockpile the charged material for use when the sun's not shining.”

The paper’s authors envision the technology could be used in countries where most people rely on burning wood or dung for cooking, which creates dangerous levels of indoor air pollution, leads to deforestation and contributes to climate change.

“For solar cooking, one would leave the device out in the sun during the day,” says Kucharski. “One design we have for such an application is purely gravity driven – the material flows from one tank to another. The flow rate is restricted so that it's exposed to the sun long enough that it gets fully charged. Then, when it's time to cook dinner, after the sun is down, the flow direction is reversed, again driven by gravity, and the opposite side of the setup is used as the cooking surface.”

“As the material flows back to the first tank, it passes by an immobilized catalyst which triggers the energy-releasing process, heating the cooking surface up,” he adds.

Other versions of such device could be used to heat buildings.
Kucharski said the MIT and Harvard team is now investigating other photoswitching molecules and substrates, “with the aim of designing a system that absorbs more of the sun's energy and also can be more practically scaled up.”

 http://www.theatlantic.com/technology/archive/2014/04/scientists-discover-how-to-generate-solar-power-in-the-dark/360679/

Scientists discover material that can be solar cell by day, light panel by night

http://phys.org/news/2014-03-scientists-material-solar-cell-day.html

This solar cell is developed from Perovskite, a promising material that could hold the key to creating high-efficiency, inexpensive solar cells. The new cells not only glow when electricity passes through them, but they can also be customised to emit different colours.
Picture this: A shopping mall facade could be storing solar energy in the day and transforms into a light display for advertisements that glows at night.
This discovery, published in top academic journal Nature Materials, was discovered almost by chance when NTU physicist Sum Tze Chien, asked his postdoctoral researcher Xing Guichuan to shine a laser on the new hybrid Perovskite solar cell material they are developing.


Read more at: http://phys.org/news/2014-03-scientists-material-solar-cell-day.html#jCp

This solar cell is developed from Perovskite, a promising material that could hold the key to creating high-efficiency, inexpensive solar cells. The new cells not only glow when electricity passes through them, but they can also be customised to emit different colours.
Picture this: A shopping mall facade could be storing solar energy in the day and transforms into a light display for advertisements that glows at night.
This discovery, published in top academic journal Nature Materials, was discovered almost by chance when NTU physicist Sum Tze Chien, asked his postdoctoral researcher Xing Guichuan to shine a laser on the new hybrid Perovskite solar cell material they are developing.


Read more at: http://phys.org/news/2014-03-scientists-material-solar-cell-day.html#jCp

This solar cell is developed from Perovskite, a promising material that could hold the key to creating high-efficiency, inexpensive solar cells. The new cells not only glow when electricity passes through them, but they can also be customised to emit different colours.
Picture this: A shopping mall facade could be storing solar energy in the day and transforms into a light display for advertisements that glows at night.
This discovery, published in top academic journal Nature Materials, was discovered almost by chance when NTU physicist Sum Tze Chien, asked his postdoctoral researcher Xing Guichuan to shine a laser on the new hybrid Perovskite solar cell material they are developing.


Read more at: http://phys.org/news/2014-03-scientists-material-solar-cell-day.html#jCp

In the future, when your mobile or tablet runs out of battery, you could just recharge it by putting it out in the sun. Nanyang Technological University (NTU) scientists have developed a next-generation solar cell material which can also emit light, in addition to converting light to electricity.

Read more at: http://phys.org/news/2014-03-scientists-material-solar-cell-day.html#jCp

A CIGS Photovoltaic Sub-Module With Conversion Efficiency Of 18.34 Percent

By putting together the formation technology for high quality light absorption layers and the advanced integration technology that had been developed at an earlier stage, the researchers achieved for the first time a high conversion efficiency, over 18 percent, of a CIGS photovoltaic sub-module. The developed technology is a core elemental technology for the improvement of the conversion efficiency of photovoltaic modules and is applicable to a wide variety of photovoltaic modules including large-area modules and flexible modules. This technology is expected to contribute to the improvement of the conversion efficiency of mass-produced photovoltaic modules, a reduction in power generation costs, and improvements in the functionality of photovoltaic modules.

http://www.photonicsonline.com/doc/a-cigs-photovoltaic-sub-module-with-conversion-efficiency-of-percent-0001

News | November 19, 2013

New Study Could Lead To Paradigm Shift In Organic Solar Cell Research

Organic solar cells have long been touted as lightweight, low-cost alternatives to rigid solar panels made of silicon. Dramatic improvements in the efficiency of organic photovoltaics have been made in recent years, yet the fundamental question of how these devices convert sunlight into electricity is still hotly debated.

Now a Stanford University research team is weighing in on the controversy. Their findings, published in the Nov. 17 issue of the journal Nature Materials, indicate that the predominant working theory is incorrect, and could steer future efforts to design materials that boost the performance of organic cells.
"We know that organic photovoltaics are very good," said study coauthor Michael McGehee, a professor of materials science and engineering at Stanford. "The question is, why are they so good? The answer is controversial."
A typical organic solar cell consists of two semiconducting layers made of plastic polymers and other flexible materials. The cell generates electricity by absorbing particles of light, or photons.
When the cell absorbs light, a photon knocks out an electron in a polymer atom, leaving behind an empty space, which scientists refer to as a hole. The electron and the hole immediately form a bonded pair called an exciton. The exciton splits, allowing the electron to move independently to a hole created by another absorbed photon. This continuous movement of electrons from hole to hole produces an electric current.
In the study, the Stanford team addressed a long-standing debate over what causes the exciton to split.
"To generate a current, you have to separate the electron and the hole," said senior author Alberto Salleo, an associate professor of materials science and engineering at Stanford. "That requires two different semiconducting materials. If the electron is attracted to material B more than material A, it drops into material B. In theory, the electron should remain bound to the hole even after it drops.
"The fundamental question that's been around a long time is, how does this bound state split?"
Some like it hot
One explanation widely accepted by scientists is known as the "hot exciton effect." The idea is that the electron carries extra energy when it drops from material A to material B. That added energy gives the excited ("hot") electron enough velocity to escape from the hole.
But that hypothesis did not stand up to experimental tests, according to the Stanford team.
"In our study, we found that the hot exciton effect does not exist," Salleo said. "We measured optical emissions from the semiconducting materials and found that extra energy is not required to split an exciton."
So what actually causes electron-hole pairs to separate?
"We haven't really answered that question yet," Salleo said. "We have a few hints. We think that the disordered arrangement of the plastic polymers in the semiconductor might help the electron get away."
In a recent study, Salleo discovered that disorder at the molecular level actually improves the performance of semiconducting polymers in solar cells. By focusing on the inherent disorder of plastic polymers, researchers could design new materials that draw electrons away from the solar cell interface where the two semiconducting layers meet, he said.
"In organic solar cells, the interface is always more disordered than the area further away," Salleo explained. "That creates a natural gradient that sucks the electron from the disordered regions into the ordered regions. "
Improving energy efficiency
The solar cells used in the experiment have an energy-conversion efficiency of about 9 percent. The Stanford team hopes to improve that performance by designing semiconductors that take advantage of the interplay between order and disorder.
"To make a better organic solar cell, people have been looking for materials that would give you a stronger hot exciton effect," Salleo said. "They should instead try to figure out how the electron gets away without it being hot. This idea is pretty controversial. It's a fundamental shift in the way people think about photocurrent generation."

SOURCE: Stanford University

http://www.photonicsonline.com/doc/new-study-could-lead-to-paradigm-shift-in-organic-solar-cell-research-0001

Color This New Solar Cell Efficiency Breakthrough Blue

The holy grail of our research is not necessarily to boost efficiencies as high as they can theoretically go, but rather to combine increases in efficiency to the kind of large-scale roll-to-roll printing or processing technologies that will help us drive down costs.
Read more at http://cleantechnica.com/2014/01/25/new-solar-cell-efficiency-breakthrough-harvests-blue-light/#jfhq1j5Du6HoudUH.99

http://cleantechnica.com/2014/01/25/new-solar-cell-efficiency-breakthrough-harvests-blue-light/

The thin film angle is important to solar cell affordability because, although thin film is not as efficient as the gold standard (that would be silicon), it is far more inexpensive to manufacture and it has a greater range of applications.
Read more at http://cleantechnica.com/2014/01/25/new-solar-cell-efficiency-breakthrough-harvests-blue-light/#jfhq1j5Du6HoudUH.99

The thin film angle is important to solar cell affordability because, although thin film is not as efficient as the gold standard (that would be silicon), it is far more inexpensive to manufacture and it has a greater range of applications.
The new Argonne solar cell research pivots on the manufacturing process to harvest more light from the blue end of the spectrum.

Read more at http://cleantechnica.com/2014/01/25/new-solar-cell-efficiency-breakthrough-harvests-blue-light/#jfhq1j5Du6HoudUH.99

The thin film angle is important to solar cell affordability because, although thin film is not as efficient as the gold standard (that would be silicon), it is far more inexpensive to manufacture and it has a greater range of applications.
The new Argonne solar cell research pivots on the manufacturing process to harvest more light from the blue end of the spectrum.

Read more at http://cleantechnica.com/2014/01/25/new-solar-cell-efficiency-breakthrough-harvests-blue-light/#jfhq1j5Du6HoudUH.99

Triangle researchers find possible solution to solar energy problem

By Jay Price

jprice@newsobserver.comJanuary 14, 2014 Updated 3 hours ago

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CHAPEL HILL — A team of researchers led by a UNC-Chapel Hill chemistry professor has discovered a potential solution to one of the fundamental problems of generating large amounts of energy from the sun’s rays: how to store some of the power so it’s available at night.
The scientists, who also include researchers from N.C. State University, found a new way to use solar energy to split molecules of water into its atomic-level components: oxygen and hydrogen. The hydrogen can then be burned for fuel, generating only water as waste, which can then be recycled to be split again.
The hydrogen could be created and used by infrastructure similar to generators and solar arrays that are already familiar, said Tom Meyer, director of the federally funded Energy Frontier Research Center at UNC-CH, who led the research.
“Part of a solar array, instead of just making electricity during the day, could in fact be making chemicals,” he said. “So when the sun goes down, you just run the chemicals through your power plant, and you extract the energy back out as you need it.”
Only a fraction of the energy being generated in the U.S. now comes from solar or from wind, which also is intermittent. But it’s enough to already create some distribution problems, and the issue is expected to increase as more renewable energy sources are added to the national grid.
Meyer had been researching how to turn solar energy into fuels for several decades while also working on other projects, he said. Parts of the process had long been apparent, but it took the addition of nanoparticle engineering to capitalize on the potential.
That’s where Gregory Parsons’ group at N.C. State University came in, said Meyer. Parsons is director of NCSU’s Nanotechnology Initiative.
The process uses two basic components. One, a molecule called a chromophore-catalyst assembly, absorbs sunlight and then begins breaking down the water molecules. The other, a nanoparticle to which thousands of chromophore-catalyst assemblies are attached, is part of a film that shuttles away electrons, a vital part of deconstructing the water molecules.
It didn’t work smoothly, though, until Meyer turned to Parsons’ team, which found a method for coating the nanoparticles with extremely thin layers of titanium dioxide. The scientists found that the nanoparticles could then carry away electrons quickly enough to make the process work well. They also figured out how to build a protective coating that keeps the chromophore-catalyst assembly tethered firmly to the nanoparticle, as the two pieces had tended to break apart.
More efficiency expected
The process currently generates hydrogen equal to about 1 percent of the energy in the sunlight received. But now that it’s clear the concept works, the researchers think there’s little doubt that they can improve the efficiency, Meyer said. They hope to reach their goal of at least 15 percent, which is similar to the efficiency of current commercial solar cells.
Also, they plan to explore the potential for using the same process to turn the greenhouse gas carbon dioxide into a carbon-based fuel such as methanol that could be burned in a closed loop, generating carbon dioxide to be used again.

Price: 919-829-4526

Read more here: http://www.newsobserver.com/2014/01/14/3532549/triangle-researchers-find-possible.html#storylink=cpy