Major U.S. solar company blames job cuts on Trump's solar import tariff

President Trump's decision to impose tariffs on imported solar materials is already taking its toll on U.S. jobs.

After putting plans on hold last month to expand its factories in the United States, SunPower Corp., one of the nation's largest solar panel manufacturers, now intends to lay off between 150 and 250 workers from its U.S. operations, or 3 percent of its global workforce, as part of a plan to cut operating expenses by 10 percent.

SunPower attributed the job cuts to the 30-percent tariffs imposed by the Trump administration on imported solar cells and panels, The Hill reported Wednesday. Company chief executive Tom Werner estimates the new tariffs will cause the company to lose $50 million in 2018 and as much as $100 million in 2019.

Werner's comments built on information that SunPower released in a filing submitted to the Securities and Exchange Commission (SEC) last week. The news also came only two weeks after SunPower reported a 35-percent decrease in revenue in 2017 compared to 2016.

Werner told The Hill that it has already begun the layoffs. Based in San Jose, California, SunPower imports most of its components from manufacturing facilities in the Philippines and Mexico.

Trump slapped the 30-percent tariff on imported solar cells and panels in January after the U.S. International Trade Commission ruled last year that China had harmed the domestic solar manufacturing industry with policies aimed at taking over the global market. The industry gets about 80 percent of its solar panel products from imports.

The Solar Energy Industries Association, the primary lobby group for the U.S. industry, estimates Trump's decision may cost the fast-growing industry about 23,000 jobs in 2018 and cause billions of dollars in solar investments to be canceled or delayed. The industry currently employees more than 260,000 people, primarily in the installation business.

The possibility that Trump would raise the price of a major component to solar photovoltaic systems contributed to a slowing of orders in 2017. This in turn helped reverse the multi-year trend in sharply rising employment.

In January, SunPower said it was putting a $20 million U.S. factory expansion and hundreds of new jobs on hold until its solar panels receive an exemption from Trump's solar tariffs. "We have to stop the $20 million investment because the tariffs start before we know if we're excluded," Werner told Reuters last month. "It's not hypothetical. These were positions that we were recruiting for that we are going to stop."

In the February 22 filing with the Securities and Exchange Commission, SunPower said it has started implementing initiatives to reduce operating expenses "in light of the known shorter-term impact of tariffs imposed on photovoltaic cells and modules." The company expects to complete the initiatives in mid-2019.

SunPower, majority-owned by Total, the French oil and gas multinational, said it expects mostly non-manufacturing employees to be affected.

Researchers improve spinach-based solar cells by adding blackberry dye

Biohybrid solar cells aren't nearly as efficient as standard silicon panels, but including natural materials in renewable energy could make it more cost-effective. Scientists have refined one design based on the proteins in spinach leaves by adding natural dye extracted from blackberries, a combination which apparently produces much more voltage than the greens alone.

A trio of just ripe blackberries on the vine.

Renewable energy researchers have been evaluating spinach-based designs for years, but biohybrid tech is still where silicon cells were 30 or 40 years ago, according to Vanderbilt School of Engineering's blog - back when the most solar powered were digital watches and calculators. Professors of the university's Chemistry and Biomolecular Engineering departments led the research on including blackberry dye with the photosystem I (PSI) molecules extracted from spinach leaves, which they described in an article published in the journal ACS Applied Energy Materials.

"We showed that this device produced about twice the photovoltage of the blackberry dye alone and 20 times that of the PSI alone," article coauthor and Vanderbilt professor Kane Jennings told the blog. While the the most the device managed to produce was 500 millivolts, it's the highest photovoltage ever recorded by the group, who have been investigating the potential of biohybrid solar cells for over a decade.

Students at Okanagan College create solar-powered table to charge cellphones

​Students at Okanagan College unveiled an outdoor table that doubles as a charging station at Okanagan College's Kelowna campus this week.

The table is the first creation by Project ReCharge - an initiative aiming to integrate solar technology with everyday objects.

The idea came when business students Nick Gallant and Cooper Simson joined with civil engineering student Josh Wiebe to find ways to charge their cellphones while enjoying the outdoors.

"A few of us had wanted to do something with solar energy," said Gallant.

"We were outside and wanted to charge our phones and work at the same time."

They enlisted the help of three more engineering students on campus to design and perfect their idea.

The group has been given the go-ahead to install similar tables at the college's Penticton, Vernon and Salmon Arm campuses.

The team will be heading to Calgary on March 1 to compete with against twelve other regional finalists and could win a spot in the national Scotiabank EcoLiving Green Challenge, which asks student teams to showcase environmentally sustainable business ideas.

They will also be competing for a $20,000 grant that will allow them to expand and get their product to market.

"We're looking at restaurants and schools and bars and areas like that, that already have existing tables but they would like to allow customers to charge their phone at the same time," said Gallant.

​

Global Selective Emitter Solar Cell Market 2021 with Key Companies Profile, Supply, Trends, Cost Structure, and SWOT Analysis

Selective Emitter Solar Cell Market

Efficiency and cost plays a vital role in the area of solar energy typically in the case of solar cells. Nowadays, there are solutions evolving for the improvement of performance in multicrystalline silicon that is based upon photovoltaic industry. Selective emitter is currently used to overcome the limitation of electrical performance in screen printed solar cells. There are two different zones in the emitter structure, one is lightly doped in the grid fingers and another is heavily doped directly under the metal contacts in the cell. In order to produce the structures of selective emitters, laser -assisted doping technique boosts regions of silicon that are beneath the contacts of solar cells.

There are several other techniques to gain selective emitters that includes dissemination masking, screen printed phosphorous doped paste, and etch-back. These techniques includes over doping by POCl3 of the emitter, adding a dopant in the metallization paste. There are several advantages of a selective-emitter cell that includes a low contact resistance because of heavy doping under the metal grid, improvement in front-surface passivation of lightly doped region in the grid. The selective emitter solar cell market is expected to expand at a healthy CAGR in the forecast period.

Key Vendors:

Tata Power Solar Systems Limited, Trina Solar Limited, SolarWorld AG, Suniva Inc, JinkoSolar Holding Co. Ltd, Pionis Energy Technologies LLC, Alps Technology Inc, Borg Inc, Itek Energy

This report studies Selective Emitter Solar Cell market, especially in North America, Europe, Asia Pacific, Middle East & Africa and Latin America and focuses on top manufacturers in the global market. They considered the production, revenue, capacity, price and market share for each manufacturer in detail.

Microeconomic and macroeconomic factors which affect the Selective Emitter Solar Cell market and its growth, both positive and negative, are also studied. The report features the impact of these factors on the ongoing market throughout the mentioned forecast period. The upcoming changing trends, factors driving as well as restricting the growth of the market are mentioned.

The investigation of the value chain and examination of the impact of Porter's five forces available on the market is likewise one of the goals of the report which incorporates the investigation of the impact of the Porter's five forces, namely, threat of substitutes, intensity of competitive rivalry, risk of new contestants, bartering power of purchasers, and bargaining power of suppliers on the market.

With all the information congregated and examined using SWOT analysis, there is a vivacious picture of the competitive landscape of the Global Selective Emitter Solar Cell Market. Openings for the future market development were revealed and preoccupied competitive dangers likewise textured. The drifts and inclinations of this market were considered and it demonstrates that there was an illustrious strategic direction observed. By the grasping market foundation and using the determined standards, methodologies, and inclinations of other driving markets for references, market data was understood.

Research N Reports is a new age market research firm where we focus on providing information that can be effectively applied. Today being a consumer driven market, companies require information to deal with the complex and dynamic world of choices. Where relying on a sound board firm for your decisions becomes crucial. Research N Reports specializes in industry analysis, market forecasts and as a result getting quality reports covering all verticals, whether be it gaining perspective on current market conditions or being ahead in the cut throat Global competition. Since we excel at business research to help businesses grow, we also offer consulting as an extended arm to our services which only helps us gain more insight into current trends and problems. Consequently we keep evolving as an all-rounder provider of viable information under one roof.

Transparent, flexible solar cells

Imagine a future in which solar cells are all around us - on windows and walls, cell phones, laptops, and more. A new flexible, transparent solar cell developed at MIT is bringing that future one step closer.

The device combines low-cost organic (carbon-containing) materials with electrodes of graphene, a flexible, transparent material made from inexpensive and abundant carbon sources. This advance in solar technology was enabled by a novel method of depositing a one-atom-thick layer of graphene onto the solar cell - without damaging nearby sensitive organic materials. Until now, developers of transparent solar cells have typically relied on expensive, brittle electrodes that tend to crack when the device is flexed. The ability to use graphene instead is making possible truly flexible, low-cost, transparent solar cells that can turn virtually any surface into a source of electric power.

Photovoltaic solar cells made of organic compounds would offer a variety of advantages over today's inorganic silicon solar cells. They would be cheaper and easier to manufacture. They would be lightweight and flexible rather than heavy, rigid, and fragile, and so would be easier to transport, including to remote regions with no central power grid. And they could be transparent. Many organic materials absorb the ultraviolet and infrared components of sunlight but transmit the visible part that our eyes can detect. Organic solar cells could therefore be mounted on surfaces all around us and harvest energy without our noticing them.

Researchers have made significant advances over the past decade toward developing transparent organic solar cells. But they've encountered one persistent stumbling block: finding suitable materials for the electrodes that carry current out of the cell.

"It's rare to find materials in nature that are both electrically conductive and optically transparent," says Professor Jing Kong of the Department of Electrical Engineering and Computer Science (EECS).

The most widely used current option is indium tin oxide (ITO). ITO is conductive and transparent, but it's also stiff and brittle, so when the organic solar cell bends, the ITO electrode tends to crack and lift off. In addition, indium is expensive and relatively rare.

A promising alternative to ITO is graphene, a form of carbon that occurs in one-atom-thick sheets and has remarkable characteristics. It's highly conductive, flexible, robust, and transparent; and it's made from inexpensive and ubiquitous carbon. In addition, a graphene electrode can be just 1 nanometer thick - a fraction as thick as an ITO electrode and a far better match for the thin organic solar cell itself.

Graphene challenges

Two key problems have slowed the wholesale adoption of graphene electrodes. The first problem is depositing the graphene electrodes onto the solar cell. Most solar cells are built on substrates such as glass or plastic. The bottom graphene electrode is deposited directly on that substrate - a task that can be achieved by processes involving water, solvents, and heat. The other layers are then added, ending with the top graphene electrode. But putting that top electrode onto the surface of the so-called hole transport layer (HTL) is tricky.

"The HTL dissolves in water, and the organic materials just below it are sensitive to pretty much anything, including water, solvents, and heat," says EECS graduate student Yi Song, a 2016-2017 Eni-MIT Energy Fellow and a member of Kong's Nanomaterials and Electronics Group. As a result, researchers have typically persisted in using an ITO electrode on the top.

The second problem with using graphene is that the two electrodes need to play different roles. The ease with which a given material lets go of electrons is a set property called its work function. But in the solar cell, just one of the electrodes should let electrons flow out easily. As a result, having both electrodes made out of graphene would require changing the work function of one of them so the electrons would know which way to go - and changing the work function of any material is not straightforward.

A smooth graphene transfer

For the past three years, Kong and Song have been working to solve these problems. They first developed and optimized a process for laying down the bottom electrode on their substrate.

In that process, they grow a sheet of graphene on copper foil. They then transfer it onto the substrate using a technique demonstrated by Kong and her colleagues in 2008. They deposit a layer of polymer on top of the graphene sheet to support it and then use an acidic solution to etch the copper foil off the back, ending up with a graphene-polymer stack that they transfer to water for rinsing. They then simply scoop up the floating graphene-polymer stack with the substrate and remove the polymer layer using heat or an acetone rinse. The result: a graphene electrode resting on the substrate.

But scooping the top electrode out of water isn't feasible. So they instead turn the floating graphene-polymer stack into a kind of stamp, by pressing a half-millimeter-thick frame of silicon rubber onto it. Grasping the frame with tweezers, they lift the stack out, dry it off, and set it down on top of the HTL. Then, with minimal warming, they can peel off the silicon rubber stamp and the polymer support layer, leaving the graphene deposited on the HTL.

Initially, the electrodes that Song and Kong fabricated using this process didn't perform well. Tests showed that the graphene layer didn't adhere tightly to the HTL, so current couldn't flow out efficiently. The obvious solutions to this problem wouldn't work. Heating the structure enough to make the graphene adhere would damage the sensitive organics. And putting some kind of glue on the bottom of the graphene before laying it down on the HTL would stick the two layers together, but would end up as an added layer between them, decreasing rather than increasing the interfacial contact.

Song decided that adding glue to the stamp might be the way to go - but not as a layer under the graphene.

"We thought, what happens if we spray this very soft, sticky polymer on top of the graphene?" he says. "It would not be in direct contact with the hole transport layer, but because graphene is so thin, perhaps its adhesive properties might remain intact through the graphene."

To test the idea, the researchers incorporated a layer of ethylene-vinyl acetate, or EVA, into their stamp, right on top of the graphene. The EVA layer is very flexible and thin - sort of like food wrap - and can easily rip apart. But they found that the polymer layer that comes next holds it together, and the arrangement worked just as Song had hoped: The EVA film adheres tightly to the HTL, conforming to any microscopic rough features on the surface and forcing the fine layer of graphene beneath it to do the same.

The process not only improved performance but also brought an unexpected side benefit. The researchers thought their next task would be to find a way to change the work function of the top graphene electrode so it would differ from that of the bottom one, ensuring smooth electron flow. But that step wasn't necessary. Their technique for laying down the graphene on the HTL actually changes the work function of the electrode to exactly what they need it to be.

"We got lucky," says Song. "Our top and bottom electrodes just happen to have the correct work functions as a result of the processes we use to make them."

Putting the electrodes to the test

To see how well their graphene electrodes would perform in practice, the researchers needed to incorporate them into functioning organic solar cells. For that task, they turned to the solar cell fabrication and testing facilities of their colleague Vladimir Bulović, the Fariborz Maseeh (1990) Professor of Emerging Technology and Associate Dean for Innovation for the School of Engineering.

For comparison, they built a series of solar cells on rigid glass substrates with electrodes made of graphene, ITO, and aluminum (a standard electrode material). The current densities (or CDs, the amount of current flowing per unit area) and power conversion efficiencies (or PCEs, the fraction of incoming solar power converted to electricity) for the new flexible graphene/graphene devices and the standard rigid ITO/graphene devices were comparable. They were lower than those of the devices with one aluminum electrode, but that was a finding they expected.

"An aluminum electrode on the bottom will reflect some of the incoming light back into the solar cell, so the device overall can absorb more of the sun's energy than a transparent device can," says Kong.

The PCEs for all their graphene/graphene devices - on rigid glass substrates as well as flexible substrates - ranged from 2.8 percent to 4.1 percent. While those values are well below the PCEs of existing commercial solar panels, they're a significant improvement over PCEs achieved in prior work involving semitransparent devices with all-graphene electrodes, the researchers say.

Measurements of the transparency of their graphene/graphene devices yielded further encouraging results. The human eye can detect light at wavelengths between about 400 nanometers and 700 nanometers. The all-graphene devices showed optical transmittance of 61 percent across the whole visible regime and up to 69 percent at 550 nanometers. "Those values [for transmittance] are among the highest for transparent solar cells with comparable power conversion efficiencies in the literature," says Kong.

Flexible substrates, bending behavior

The researchers note that their organic solar cell can be deposited on any kind of surface, rigid or flexible, transparent or not. "If you want to put it on the surface of your car, for instance, it won't look bad," says Kong. "You'll be able to see through to what was originally there."

To demonstrate that versatility, they deposited their graphene-graphene devices onto flexible substrates including plastic, opaque paper, and translucent Kapton tape. Measurements show that the performance of the devices is roughly equal on the three flexible substrates - and only slightly lower than those made on glass, likely because the surfaces are rougher so there's a greater potential for poor contact.

The ability to deposit the solar cell on any surface makes it promising for use on consumer electronics - a field that's growing rapidly worldwide. For example, solar cells could be fabricated directly on cell phones and laptops rather than made separately and then installed, a change that would significantly reduce manufacturing costs.

They would also be well-suited for future devices such as peel-and-stick solar cells and paper electronics. Since those devices would inevitably be bent and folded, the researchers subjected their samples to the same treatment. While all of their devices - including those with ITO electrodes - could be folded repeatedly, those with graphene electrodes could be bent far more tightly before their output started to decline.

Future goals

The researchers are now working to improve the efficiency of their graphene-based organic solar cells without sacrificing transparency. (Increasing the amount of active area would push up the PCE, but transparency would drop.) According to their calculations, the maximum theoretical PCE achievable at their current level of transparency is 10 percent.

"Our best PCE is about 4 percent, so we still have some way to go," says Song.

They're also now considering how best to scale up their solar cells into the large-area devices needed to cover entire windows and walls, where they could efficiently generate power while remaining virtually invisible to the human eye.

This research was supported by the Italian energy company Eni S.p.A. as part of the Eni-MIT Alliance Solar Frontiers Center. Eni is a Founding Member of the MIT Energy Initiative.

This article appeared in the Spring 2017 issue of Energy Futures, the magazine of the MIT Energy Initiative.

Plasmon-powered devices for medicine, security, solar cells

A Rice University professor's method to "upconvert" light could make solar cells more efficient and disease-targeting nanoparticles more effective.

Experiments led by Gururaj Naik, an assistant professor of electrical and computer engineering, combined plasmonic metals and semiconducting quantum wells to boost the frequency of light, changing its color.

In a nanoscale prototype Naik developed as a postdoctoral researcher at Stanford University, custom-designed pylons that were struck by green light produced a higher-energy blue glow. "I'm taking low-energy photons and converting them to high-energy photons," he said.

Efficient upconversion of light could let solar cells turn otherwise-wasted infrared sunlight into electricity or help light-activated nanoparticles treat diseased cells, Naik said.

The work appears in the American Chemical Society's Nano Letters.

The magic happens inside tiny pylons that measure about 100 nanometers across. When excited by a specific wavelength of light, specks of gold on the tips of the pylons convert the light energy into plasmons, waves of energy that slosh rhythmically across the gold surface like ripples on a pond. Plasmons are short-lived, and when they decay, they give up their energy in one of two ways; they either emit a photon of light or produce heat by transferring their energy to a single electron - a "hot" electron.

Naik's work at Stanford was inspired by the groundbreaking work of professors Naomi Halas and Peter Nordlander at Rice's Laboratory for Nanophotonics, who had shown that exciting plasmonic materials also excited "hot carriers" - electrons and holes - within. (Electron holes are the vacancies created when an electron is excited into a higher state, giving its atom a positive charge.)

Gururaj Naik is developing technology to upconvert light by using lasers to power devices that combine plasmonic metals and semiconducting quantum wells. Credit: Tommy LaVergne/Rice University

"Plasmonics is really great at squeezing light on the nanoscale," said Naik, who joined Rice's faculty a year ago. "But that always comes at the cost of something. Halas and Nordlander showed you can extract the optical losses in the form of electricity. My idea was to put them back to optical form."

He designed pylons using alternate layers of gallium nitride and indium gallium nitride that were topped with a thin layer of gold and surrounded by silver. Instead of letting the hot carriers slip away, Naik's strategy was to direct both hot electrons and hot holes toward the gallium nitride and indium gallium nitride bases that serve as electron-trapping quantum wells. These wells have an inherent bandgap that sequesters electrons and holes until they recombine at sufficient energy to leap the gap and release photons at a higher frequency.

Present-day upconverters used in on-chip communications, photodynamic therapy, security and data storage have efficiencies in the range of 5 to 10 percent, Naik said. Quantum theory offers a maximum 50 percent efficiency ("because we're absorbing two photons to emit one") but, he said, 25 percent is a practical goal for his method.

Naik noted his devices can be tuned by changing the size and shape of the particles and thickness of the layers. "Upconverters based on lanthanides and organic molecules emit and absorb light at set frequencies because they're fixed by atomic or molecular energy levels," he said. "We can design quantum wells and tune their bandgaps to emit photons in the frequency range we want and similarly design metal nanostructures to absorb at different frequencies. That means we can design absorption and emission almost independently, which was not possible before."

Naik built and tested a proof-of-concept prototype of the pylon array while working in the Stanford lab of Jennifer Dionne after co-authoring a theoretical paper with her that set the stage for the experiments.

"That's a solid-state device," Naik said of the prototype. "The next step is to make standalone particles by coating quantum dots with metal at just the right size and shape."

These show promise as medical contrast agents or drug-delivery vehicles, he said. "Infrared light penetrates deeper into tissues, and blue light can cause the reactions necessary for the delivery of medicine," Naik said. "People use upconverters with drugs, deliver them to the desired part of the body, and shine infrared light from the outside to deliver and activate the drug."

The particles would also make a mean invisible ink, he said. "You can write with an upconverter and nobody would know until you shine high-intensity infrared on it and it upconverts to visible light."

Solar cells more efficient

UC Riverside researchers find a way to use the infrared region of the sun's spectrum to make solar cells more efficient

By Iqbal Pittalwala on July 27, 2015

RIVERSIDE, Calif. - When it comes to installing solar cells, labor cost and the cost of the land to house them constitute the bulk of the expense. The solar cells - made often of silicon or cadmium telluride - rarely cost more than 20 percent of the total cost. Solar energy could be made cheaper if less land had to be purchased to accommodate solar panels, best achieved if each solar cell could be coaxed to generate more power.

A huge gain in this direction has now been made by a team of chemists at the University of California, Riverside that has found an ingenious way to make solar energy conversion more efficient. The researchers report in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in "upconverting" photons in the visible and near-infrared regions of the solar spectrum.

"The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today's solar cells," explained Christopher Bardeen, a professor of chemistry. The research was a collaborative effort between him and Ming Lee Tang, an assistant professor of chemistry. "This is energy lost, no matter how good your solar cell. The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity, then adds their energies together to make one higher energy photon. This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted."

Bardeen added that these materials are essentially "reshaping the solar spectrum" so that it better matches the photovoltaic materials used today in solar cells. The ability to utilize the infrared portion of the solar spectrum could boost solar photovoltaic efficiencies by 30 percent or more.

In their experiments, Bardeen and Tang worked with cadmium selenide and lead selenide semiconductor nanocrystals. The organic compounds they used to prepare the hybrids were diphenylanthracene and rubrene. The cadmium selenide nanocrystals could convert visible wavelengths to ultraviolet photons, while the lead selenide nanocrystals could convert near-infrared photons to visible photons.

In lab experiments, the researchers directed 980-nanometer infrared light at the hybrid material, which then generated upconverted orange/yellow fluorescent 550-nanometer light, almost doubling the energy of the incoming photons. The researchers were able to boost the upconversion process by up to three orders of magnitude by coating the cadmium selenide nanocrystals with organic ligands, providing a route to higher efficiencies.

"This 550-nanometer light can be absorbed by any solar cell material," Bardeen said. "The key to this research is the hybrid composite material - combining inorganic semiconductor nanoparticles with organic compounds. Organic compounds cannot absorb in the infrared but are good at combining two lower energy photons to a higher energy photon. By using a hybrid material, the inorganic component absorbs two photons and passes their energy on to the organic component for combination. The organic compounds then produce one high-energy photon. Put simply, the inorganics in the composite material take light in; the organics get light out."

Besides solar energy, the ability to upconvert two low energy photons into one high energy photon has potential applications in biological imaging, data storage and organic light-emitting diodes. Bardeen emphasized that the research could have wide-ranging implications.

"The ability to move light energy from one wavelength to another, more useful region, for example, from red to blue, can impact any technology that involves photons as inputs or outputs," he said.

The research was supported by grants from the National Science Foundation and the U.S. Army.

The research was conducted also by the following coauthors on the research paper: Zhiyuan Huang (first author), Xin Li, Melika Mahboub, Kerry M. Hanson, Valerie M. Nichols and Hoang Le.

Tang's group helped design the experiments and provided the nanocrystals.

The UCR Office of Technology Commercialization has filed a provisional patent on the technology.

Archived under:Science/Technology, chemistry, Christopher Bardeen, CNAS, College of Natural and Agricultural Sciences, electricity, green, Ming Lee Tang, nanocrystals, nanoparticles, National Science Foundation, Office of Technology Commercialization, press release, solar, solar cells, solar energy, solar panels, upconversion

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New solar cell

The UT Arlington team developed a new solar cell that is more efficient and can store solar energy even at night. Credit: UT Arlington 

A University of Texas at Arlington materials science and engineering team has developed a new energy cell that can store large-scale solar energy even when it's dark.

The innovation is an advancement over the most common solar energy systems that rely on using sunlight immediately as a power source. Those systems are hindered by not being able to use that solar energy at night or when cloudy conditions exist.

The UT Arlington team developed an all-vanadium photo-electrochemical flow cell that allows for efficient and large-scale solar energy storage even at nighttime. The team is now working on a larger prototype.

"This research has a chance to rewrite how we store and use solar power," said Fuqiang Liu, an assistant professor in the Materials Science and Engineering Department who led the research team. "As renewable energy becomes more prevalent, the ability to store solar energy and use it as a renewable alternative provides a sustainable solution to the problem of energy shortage. It also can effectively harness the inexhaustible energy from the sun."

The work is a product of the 2013 National Science Foundation $400,000 Faculty Early Career Development grant awarded to Liu to improve the way solar energy is captured, stored and transmitted for use. Other members of the team included lead author Dong Liu, who recently defended his UT Arlington Ph.D. dissertation in 2015, and Zi Wei, a UT Arlington doctoral candidate.

The research is detailed in "Reversible Electron Storage in an All-Vanadium Photoelectrochemical Storage Cell: Synergy between Vanadium Redox and Hybrid Photocatalyst," in the most recent edition of the American Chemical Society journal ACS Catalysis.

Khosrow Behbehani, dean of the College of Engineering, said the groundbreaking research has the potential to positively impact on the way we generate and consume energy.

Dong Liu (left), Zi Wei (center) and Fuqiang Liu, an assistant professor in the UT Arlington Materials Science and Engineering Department are shown. Credit: UT Arlington 

"Dr. Liu and his colleagues are working to help us shape a more sustainable future and are taking innovative steps to improve our ability to harness and use one of the larger sources of energy available to us - the sun," Behbehani said. 

Dong Liu, lead author of the paper, said a major drawback of current solar technology is the limitation on storing energy under dark conditions.

"We have demonstrated simultaneously reversible storage of both solar energy and electrons in the cell," Dong Liu said. "Release of the stored electrons under dark conditions continues solar energy storage, thus allowing for unintermittent storage around the clock."

Wei, another co-author of the paper, said that the research should allow solar energy storage to be done in a much higher capacity and on a much larger scale.

"Using an all-vanadium photo-electrochemical cell gives our energy storage an edge over other systems," Wei said. "This cell allows us to attain higher storage capacity in a smaller unit. " 

The solar cells 13.6%

Imágenes topológicas de películas de silicio sobre las estructuras de nido de abeja, que es lo que los investigadores utilizan para diseñar las nuevas células solares. Crédito: Sai, et al. © 2015 AIP Publishing 

(Phys.org) - En un nuevo estudio, los científicos han reportado un récord mundial estabilizado eficiencia de 13,6% para una célula de película delgada de silicio solar de triple unión, que es una versión más reciente de la célula solar de silicio de película delgada de un solo cruce que ha sido utilizado en productos comerciales desde la década de 1970. Este valor bordes a cabo el récord anterior de 13,44%, y los investigadores esperan que algunas mejoras razonables empujarán por encima de 14%.

. El equipo de investigación, Hitoshi Sai, y otros, consiste en una colaboración de varios de japoneses mayores centros de investigación: el Instituto Nacional de Ciencia Industrial Avanzada y Tecnología (AIST), la Asociación Fotovoltaica Power Generation Technology Research (PVTEC), Sharp, Panasonic , y Mitsubishi. 

"Creemos que este trabajo se presentan dos resultados importantes", Sai, investigador de la AIST, dijo Phys.org. "El primero es la eficiencia más alta del mundo en las células solares de silicio de película delgada sobre la base de una función de la luz que atrapa el avanzado. Y en segundo lugar, la característica que atrapan la luz avanzada nos permite alcanzar una alta densidad de fotocorriente potencial (34,1 mA / cm2), con sólo un 4-um-gruesa capa absorbente microcristalina. Con estos resultados, se demostró con éxito cómo la luz que atrapa la tecnología puede contribuir a impulsar la fotocorriente y la eficiencia de las células solares ".

Debido a que hay muchos tipos diferentes de eficiencia cuando se trata de células solares, a menudo es difícil para los no especialistas que se pueden hacer comparaciones directas. Como explican los investigadores en su artículo publicado en Applied Physics Letters, eficiencia estabilizada es la eficiencia de conversión de energía (PCE) que da cuenta de la degradación inducida por la luz. La diferencia puede ser significativa, con eficiencias estabilizadas de alrededor de 13% que tienen PCE tan altas como 16% - una diferencia de aproximadamente 20%.

Spectra de la película delgada de triple unión célula solar de silicio récord, revelando tres picos de absorción de longitud de onda diferentes (o "densidades de corriente") que corresponden a los tres subcélulas. Crédito: Sai, et al. © 2015 AIP Publishing 

"A veces la eficiencia de células solares causa confusión, ya que hay varias definiciones," explicó Sai. "En general, cualquier tipo de muestra de células solares diversos grados de degradación frente a la exposición prolongada a la luz, la humedad, la temperatura, y así sucesivamente. Sin embargo, la mayoría de las células solares se evalúan por su eficacia 'inicial'. Si la célula solar es relativamente estable, células solares tales como silicio cristalino son, está bien. Sin embargo, es bien sabido que el silicio amorfo muestra una degradación significativa contra exposición a la luz prolongada, llamado el efecto Steabler-Wronski, tal como se describe en nuestro documento. Para hacer una comparación justa, en este campo, que compara el rendimiento de células solares después de un procedimiento de luz remojo común ".

Numerosos factores probablemente contribuyen a la degradación inducida por la luz en las células solares de silicio, aunque los mecanismos exactos no se entienden completamente. Uno de los métodos de diseño para reducir la degradación inducida por la luz consiste en la fabricación de las células solares en sustratos de panal con textura. Hasta el momento, las texturas de nido de abeja en su mayoría se han utilizado para las células solares de una sola unión, que están hechas de un solo material semiconductor y así pueden absorber la luz de una sola longitud de onda. 

En el nuevo papel, los científicos verifican investigaciones recientes que muestran que la textura de panal también se puede utilizar para hacer crecer células solares multiunión. Dado que las células multiunión solar constan de más de un material semiconductor, que pueden absorber múltiples longitudes de onda de la luz. Al igual que con las células solares de una sola unión, las células solares de triple unión fabricados aquí exhiben un efecto de luz que atrapa superior debido a la textura de panal.

Para mejorar aún más la eficiencia, los investigadores también controlan cuidadosamente el período de la textura de nido de abeja, incorporan una película anti-reflexión sobre la base de una estructura de polilla-ojo, y posicionados las tres capas a fin de maximizar la eficiencia, entre otras estrategias.

Al probar la célula solar en su propio laboratorio, los investigadores obtuvieron inicial y estabilizadas eficiencias de aproximadamente 14,5% y 13,8%, respectivamente, lo que indica una degradación de la eficiencia inducida por la luz de menos de 5%. La célula solar también se caracterizó de forma independiente por el AIST, que obtuvo un funcionario ligeramente inferior estabiliza eficiencia del 13,6%. Los investigadores explican que la discrepancia probablemente se debe a las diferencias en los simuladores solares utilizados en las pruebas: propio laboratorio de los científicos utilizó un simulador solar de doble luz, lo que es más rica en longitudes de onda azules que el simulador solar de triple luz más exacto utilizado en el AIST laboratorio. La célula solar se optimizó para el espectro generado por el simulador solar de doble luz.

A pesar de establecer un nuevo récord, los investigadores creen que todavía hay mucho margen de mejora, en particular mejorando el rendimiento de la capa superior de la célula solar de triple capa y al abordar el desajuste espectral. Al mejorar en estas áreas, predicen que este enfoque logrará una eficiencia estabilizado por encima de 14% en un futuro próximo. Además, los investigadores les gustaría aplicar este nuevo conocimiento sobre la captura de luz a las células solares de silicio basados ​​en obleas convencionales.