Third-Generation Solar Cells using Metalorganic Perovskites Challenges silicon based Solar Cells


nanotubefilmAn illustration of a perovskite solar cell. Credit: Photo by Aalto University / University of Uppsala / EPFL

Five years ago, the world started to talk about third-generation solar cells that challenged the traditional silicon cells with a cheaper and simpler manufacturing process that used less energy.

Methylammonium lead iodide is a metal-organic material in the perovskite crystal structure that captures light efficiently and conducts electricity well—both important qualities in . However, the lifetime of solar cells made of metalorganic perovskites has proven to be very short compared to cells made of .

Now researchers from Aalto University, Uppsala University and École polytechnique fédérale de Lausanne (EPFL) in Switzerland have managed to improve the long term stability of solar cells made of perovskite using “random network” nanotube films developed under the leadership of Professor Esko Kauppinen at Aalto University. Random network nanotube films are films composed of single-walled carbon nanotubes that in an electron microscope image look like spaghetti on a plate.

‘In a traditional perovskite solar cell, the hole conductor layer consists of organic material and, on top of it, a thin layer of gold that easily starts to disintegrate and diffuse through the whole solar cell structure. We replaced the gold and also part of the organic material with films made of carbon nanotubes and achieved good cell stability in 60 degrees and full one sun illumination conditions‘, explains Kerttu Aitola, who defended her doctoral dissertation at Aalto University and now works as a researcher at Uppsala University

In the study, thick black films with conductivity as high as possible were used in the back contact of the solar cell where light does not need to get through. According to Aitola, nanotube films can also be made transparent and thin, which would make it possible to use them as the front contact of the cell, in other words as the contact that lets light through.

‘The solar cells were prepared in Uppsala and the long-term stability measurement was carried out at EPFL. The leader of the solar cell group at EPFL is Professor Michael Grätzel, who was awarded the Millennium Prize 2010 for dye-sensitised solar cells, on which the are also partly based on’, says Aitola.

Nanotube film may resolve longevity problem of challenger solar cells
Cross-section of the solar cell in an electron microscope image. The fluff seen in the front of the image is composed of bundles of nanotubes that have become half-loose when the samples have been prepared for imaging. Credit: Photo by Aalto University / University of Uppsala / EPFL

 

The lifetime of solar cells made of silicon is 20-30 years and their industrial production is very efficient. Still, alternatives are needed as reducing the silicon dioxide in sand to silicon consumes a huge amount of energy. It is estimated that a needs two or three years to produce the energy that was used to manufacture it, whereas a perovskite solar cell would only need two or three months to do it.

‘In addition, the silicon used in solar cells must be extremely pure’, says Aitola.

‘Perovskite solar cell is also interesting because its efficiency, in other words how efficiently it converts sunlight energy into electrical energy, has very quickly reached the level of silicon solar cells. That is why so much research is conducted on perovskite solar cells globally.’

The alternative solar cells are even more interesting because of their various application areas. Flexible solar cells have until now been manufactured on conductive plastic. Compared with the conductive layer of plastic, the flexibility of nanotube films is superior and the raw materials are cheaper. Thanks to their flexibility, solar cells could be produced using the roll-to-roll processing method known from the paper industry.

‘Light and would be easy to integrate in buildings and you could also hang them in windows by yourself’, says Aitola.

Explore further: New way to make low-cost solar cell technology

More information: Kerttu Aitola et al, High Temperature-Stable Perovskite Solar Cell Based on Low-Cost Carbon Nanotube Hole Contact, Advanced Materials (2017). DOI: 10.1002/adma.201606398

Stanford and Oxford scientists report New Perovskite low cost solar cell design could outperform existing commercial technologies: Video


stanford-oxfoed-perovskite_news-960x640Researchers have created a new type of solar cell that replaces silicon with a crystal called perovskite. This design converts sunlight to electricity at efficiencies similar to current technology but at much lower cost.

A new design for solar cells that uses inexpensive, commonly available materials could rival and even outperform conventional cells made of silicon.

Stanford and Oxford have created novel solar cells from crystalline perovskite that could outperform existing silicon cells on the market today. This design converts sunlight to electricity at efficiencies of 20 percent, similar to current technology but at much lower cost.

 

Writing in the Oct. 21 edition of Science, researchers from Stanford and Oxford describe using tin and other abundant elements to create novel forms of perovskite – a photovoltaic crystalline material that’s thinner, more flexible and easier to manufacture than silicon crystals.

Video: Stanford and Oxford scientists have created novel solar cells from crystalline perovskite that could rival and even outperform existing silicon cells on the market today. The new design converts sunlight to electricity at efficiencies of 20 percent, similar to current technology but at much lower cost.

In the video, Professor Michael McGehee and postdoctoral scholar Tomas Leijtens of Stanford describe the discovery, which could lead to thin-film solar cells with a record-setting 30% efficiency.

“Perovskite semiconductors have shown great promise for making high-efficiency solar cells at low cost,” said study co-author Michael McGehee, a professor of materials science and engineering at Stanford. “We have designed a robust, all-perovskite device that converts sunlight into electricity with an efficiency of 20.3 percent, a rate comparable to silicon solar cells on the market today.”

The new device consists of two perovskite solar cells stacked in tandem. Each cell is printed on glass, but the same technology could be used to print the cells on plastic, McGehee added.

“The all-perovskite tandem cells we have demonstrated clearly outline a roadmap for thin-film solar cells to deliver over 30 percent efficiency,” said co-author Henry Snaith, a professor of physics at Oxford. “This is just the beginning.”

Tandem technology

Previous studies showed that adding a layer of perovskite can improve the efficiency of silicon solar cells. But a tandem device consisting of two all-perovskite cells would be cheaper and less energy-intensive to build, the authors said.

Stanford post-doctoral scholar Tomas Leijtens and Professor Mike McGehee examine perovskite tandem solar cells.

Stanford post-doctoral scholar Tomas Leijtens and Professor Mike McGehee examine perovskite tandem solar cells. (Image credit: L.A. Cicero)

“A silicon solar panel begins by converting silica rock into silicon crystals through a process that involves temperatures above 3,000 degrees Fahrenheit (1,600 degrees Celsius),” said co-lead author Tomas Leijtens, a postdoctoral scholar at Stanford. “Perovskite cells can be processed in a laboratory from common materials like lead, tin and bromine, then printed on glass at room temperature.”

But building an all-perovskite tandem device has been a difficult challenge. The main problem is creating stable perovskite materials capable of capturing enough energy from the sun to produce a decent voltage.

A typical perovskite cell harvests photons from the visible part of the solar spectrum. Higher-energy photons can cause electrons in the perovskite crystal to jump across an “energy gap” and create an electric current.

A solar cell with a small energy gap can absorb most photons but produces a very low voltage. A cell with a larger energy gap generates a higher voltage, but lower-energy photons pass right through it.

An efficient tandem device would consist of two ideally matched cells, said co-lead author Giles Eperon, an Oxford postdoctoral scholar currently at the University of Washington.

“The cell with the larger energy gap would absorb higher-energy photons and generate an additional voltage,” Eperon said. “The cell with the smaller energy gap can harvest photons that aren’t collected by the first cell and still produce a voltage.”

Cross-section of new tandem solar cell

Cross-section of a new tandem solar cell designed by Stanford and Oxford scientists. The brown upper layer of perovskite captures low-energy lightwaves, and the red perovskite layer captures high-energy waves. (Image credit: Scanning electron microscopy image by Rebecca Belisle and Giles Eperon)

The smaller gap has proven to be the bigger challenge for scientists. Working together, Eperon and Leijtens used a unique combination of tin, lead, cesium, iodine and organic materials to create an efficient cell with a small energy gap.

“We developed a novel perovskite that absorbs lower-energy infrared light and delivers a 14.8 percent conversion efficiency,” Eperon said. “We then combined it with a perovskite cell composed of similar materials but with a larger energy gap.”

The result: A tandem device consisting of two perovskite cells with a combined efficiency of 20.3 percent.

“There are thousands of possible compounds for perovskites,” Leijtens added, “but this one works very well, quite a bit better than anything before it.”

Seeking stability

One concern with perovskites is stability. Rooftop solar panels made of silicon typically last 25 years or more. But some perovskites degrade quickly when exposed to moisture or light. In previous experiments, perovskites made with tin were found to be particularly unstable.

To assess stability, the research team subjected both experimental cells to temperatures of 212 degrees Fahrenheit (100 degrees Celsius) for four days.

“Crucially, we found that our cells exhibit excellent thermal and atmospheric stability, unprecedented for tin-based perovskites,” the authors wrote.

“The efficiency of our tandem device is already far in excess of the best tandem solar cells made with other low-cost semiconductors, such as organic small molecules and microcrystalline silicon,” McGehee said. “Those who see the potential realize that these results are amazing.”

The next step is to optimize the composition of the materials to absorb more light and generate an even higher current, Snaith said.

“The versatility of perovskites, the low cost of materials and manufacturing, now coupled with the potential to achieve very high efficiencies, will be transformative to the photovoltaic industry once manufacturability and acceptable stability are also proven,” he said.

Co-author Stacey Bent, a professor of chemical engineering at Stanford, provided key insights on tandem-fabrication techniques. Other Stanford coauthors are Kevin Bush, Rohit Prasanna, Richard May, Axel Palmstrom, Daniel J. Slotcavage and Rebecca Belisle. Oxford co-authors are Thomas Green, Jacob Tse-Wei Wang, David McMeekin, George Volonakis, Rebecca Milot, Jay Patel, Elizabeth S. Parrott, Rebecca Sutton, Laura Herz, Michael Johnston and Henry Snaith. Other co-authors are Bert Conings, Aslihan Babayigit and Hans-Gerd Boyen of Hasselt University in Belgium, and Wen Ma and Farhad Moghadam of SunPreme Inc.

Funding was provided by the Graphene Flagship, The Leverhulme Trust, U.K. Engineering and Physical Sciences Research Council, European Union Seventh Framework Programme, Horizon 2020, U.S. Office of Naval Research and the Global Climate and Energy Project at Stanford.

 

U of Toronto: A Printable Solar Cell Closer to Commercial Reality


u-toronto-solar-cell-id45884A University of Toronto Engineering innovation could make printing solar cells as easy and inexpensive as printing a newspaper.

Dr. Hairen Tan and his team have cleared a critical manufacturing hurdle in the development of a relatively new class of solar devices called perovskite solar cells. This alternative solar technology could lead to low-cost, printable solar panels capable of turning nearly any surface into a power generator.

 

“Economies of scale have greatly reduced the cost of silicon manufacturing,” said Professor Ted Sargent, an expert in emerging solar technologies and the Canada Research Chair in Nanotechnology. “Perovskite solar cells can enable us to use techniques already established in the printing industry to produce solar cells at very low cost. Potentially, perovskites and silicon cells can be married to improve efficiency further, but only with advances in low-temperature processes.”

 

Perovskite Solar Cell
The new perovskite solar cells have achieved an efficiency of 20.1 per cent and can be manufactured at low temperatures, which reduces the cost and expands the number of possible applications. (Image: Kevin Soobrian)

 

Today, virtually all commercial solar cells are made from thin slices of crystalline silicon which must be processed to a very high purity. It’s an energy-intensive process, requiring temperatures higher than 1,000 degrees Celsius and large amounts of hazardous solvents.
In contrast, perovskite solar cells depend on a layer of tiny crystals — each about 1,000 times smaller than the width of a human hair — made of low-cost, light-sensitive materials. Because the perovskite raw materials can be mixed into a liquid to form a kind of ‘solar ink’, they could be printed onto glass, plastic or other materials using a simple inkjet printing process.
But, until now, there’s been a catch: in order to generate electricity, electrons excited by solar energy must be extracted from the crystals so they can flow through a circuit. That extraction happens in a special layer called the electron selective layer, or ESL. The difficulty of manufacturing a good ESL has been one of the key challenges holding back the development of perovskite solar cell devices.
“The most effective materials for making ESLs start as a powder and have to be baked at high temperatures, above 500 degrees Celsius,” said Tan. “You can’t put that on top of a sheet of flexible plastic or on a fully fabricated silicon cell — it will just melt.”
Tan and his colleagues developed a new chemical reaction than enables them to grow an ESL made of nanoparticles in solution, directly on top of the electrode. While heat is still required, the process always stays below 150 degrees C, much lower than the melting point of many plastics.
The new nanoparticles are coated with a layer of chlorine atoms, which helps them bind to the perovskite layer on top — this strong binding allows for efficient extraction of electrons. In a paper recently published in Science (“Efficient and stable solution-processed planar perovskite solar cells via contact passivation”), Tan and his colleagues report the efficiency of solar cells made using the new method at 20.1 per cent.
“This is the best ever reported for low-temperature processing techniques,” said Tan. He adds that perovskite solar cells using the older, high-temperature method are only marginally better at 22.1 per cent, and even the best silicon solar cells can only reach 26.3 per cent.
Another advantage is stability. Many perovskite solar cells experience a severe drop in performance after only a few hours, but Tan’s cells retained more than 90 per cent of their efficiency even after 500 hours of use. “I think our new technique paves the way toward solving this problem,” said Tan, who undertook this work as part of a Rubicon Fellowship.
“The Toronto team’s computational studies beautifully explain the role of the newly developed electron-selective layer. The work illustrates the rapidly-advancing contribution that computational materials science is making towards rational, next-generation energy devices,” said Professor Alan Aspuru-Guzik, an expert on computational materials science in the Department of Chemistry and Chemical Biology at Harvard University, who was not involved in the work.
“To augment the best silicon solar cells, next-generation thin-film technologies need to be process-compatible with a finished cell. This entails modest processing temperatures such as those in the Toronto group’s advance reported in Science,” said Professor Luping Yu of the University of Chicago’s Department of Chemistry. Yu is an expert on solution-processed solar cells and was not involved in the work.
Keeping cool during the manufacturing process opens up a world of possibilities for applications of perovskite solar cells, from smartphone covers that provide charging capabilities to solar-active tinted windows that offset building energy use. In the nearer term, Tan’s technology could be used in tandem with conventional solar cells.
“With our low-temperature process, we could coat our perovskite cells directly on top of silicon without damaging the underlying material,” said Tan. “If a hybrid perovskite-silicon cell can push the efficiency up to 30 per cent or higher, it makes solar power a much better economic proposition.”
Source: University of Toronto

 

Tesla And Panasonic Finalize Solar Cell Production Agreement


Japanese electronics company Panasonic and U.S. electric car manufacture Tesla announced Tuesday that they have finalized an agreement, and will begin production of solar cells at a factory in Buffalo, New York.

In a statement released on Tuesday, the two companies said they plan to start production of photovoltaic (PV) cells and modules in the summer of 2017.

Panasonic will be investing more than $256 million in a New York production facility of Tesla Motors, and has agreed to pay capital costs for the manufacturing. In return, Tesla has made a “long-term purchase commitment” to Panasonic.

Tesla said this agreement will create 1,400 jobs in Buffalo, including 500 in manufacturing, and plans further expansion in Buffalo.

JB Straubel, Chief Technical Officer and Co-founder of Tesla, said “We are excited to expand our partnership with Panasonic as we move towards a combined Tesla and SolarCity.
By working together on solar, we will be able to accelerate production of high-efficiency, extremely reliable solar cells and modules at the best cost.”

The Associated Press reported:

SolarCity has committed to investing $5 billion over 10 years in New York state, hiring almost 1,500 workers at the Buffalo plant for five years and employing at least 2,000 more people across New York in exchange for use of the state-owned plant.

This plan is part of the solar partnership that the two companies first announced in October.

Physics, photosynthesis and ‘Green’ solar cells


green-solar-cells-161130154310_1_540x360
In a light harvesting quantum photocell, particles of light (photons) can efficiently generate electrons. When two absorbing channels are used, solar power entering the system through the two absorbers (a and b) efficiently generates power in the machine (M). Credit: Nathaniel Gabor and Tamar Melen

A University of California, Riverside assistant professor has combined photosynthesis and physics to make a key discovery that could help make solar cells more efficient. The findings were recently published in the journal Nano Letters.

Nathan Gabor is focused on experimental condensed matter physics, and uses light to probe the fundamental laws of quantum mechanics. But, he got interested in photosynthesis when a question popped into his head in 2010: Why are plants green? He soon discovered that no one really knows.

During the past six years, he sought to help change that by combining his background in physics with a deep dive into biology.

He set out to re-think solar energy conversion by asking the question: can we make materials for solar cells that more efficiently absorb the fluctuating amount of energy from the sun. Plants have evolved to do this, but current affordable solar cells — which are at best 20 percent efficient — do not control these sudden changes in solar power, Gabor said. That results in a lot of wasted energy and helps prevent wide-scale adoption of solar cells as an energy source.

Gabor, and several other UC Riverside physicists, addressed the problem by designing a new type of quantum heat engine photocell, which helps manipulate the flow of energy in solar cells. The design incorporates a heat engine photocell that absorbs photons from the sun and converts the photon energy into electricity.

Surprisingly, the researchers found that the quantum heat engine photocell could regulate solar power conversion without requiring active feedback or adaptive control mechanisms. In conventional photovoltaic technology, which is used on rooftops and solar farms today, fluctuations in solar power must be suppressed by voltage converters and feedback controllers, which dramatically reduce the overall efficiency.

The goal of the UC Riverside teams was to design the simplest photocell that matches the amount of solar power from the sun as close as possible to the average power demand and to suppress energy fluctuations to avoid the accumulation of excess energy.

The researchers compared the two simplest quantum mechanical photocell systems: one in which the photocell absorbed only a single color of light, and the other in which the photocell absorbed two colors. They found that by simply incorporating two photon-absorbing channels, rather than only one, the regulation of energy flow emerges naturally within the photocell.

The basic operating principle is that one channel absorbs at a wavelength for which the average input power is high, while the other absorbs at low power. The photocell switches between high and low power to convert varying levels of solar power into a steady-state output.

When Gabor’s team applied these simple models to the measured solar spectrum on Earth’s surface, they discovered that the absorption of green light, the most radiant portion of the solar power spectrum per unit wavelength, provides no regulatory benefit and should therefore be avoided. They systematically optimized the photocell parameters to reduce solar energy fluctuations, and found that the absorption spectrum looks nearly identical to the absorption spectrum observed in photosynthetic green plants.

The findings led the researchers to propose that natural regulation of energy they found in the quantum heat engine photocell may play a critical role in the photosynthesis in plants, perhaps explaining the predominance of green plants on Earth.

Other researchers have recently found that several molecular structures in plants, including chlorophyll a and b molecules, could be critical in preventing the accumulation of excess energy in plants, which could kill them. The UC Riverside researchers found that the molecular structure of the quantum heat engine photocell they studied is very similar to the structure of photosynthetic molecules that incorporate pairs of chlorophyll.

The hypothesis set out by Gabor and his team is the first to connect quantum mechanical structure to the greenness of plants, and provides a clear set of tests for researchers aiming to verify natural regulation. Equally important, their design allows regulation without active input, a process made possible by the photocell’s quantum mechanical structure.


Story Source:

Materials provided by University of California – Riverside. Original written by Sean Nealon. Note: Content may be edited for style and length.


Journal Reference:

  1. Trevor B. Arp, Yafis Barlas, Vivek Aji, Nathaniel M. Gabor. Natural Regulation of Energy Flow in a Green Quantum Photocell. Nano Letters, 2016; DOI: 10.1021/acs.nanolett.6b03136

Perovskite solar cells hit new world efficiency record


Dr. Anita Ho-Baillie, a Senior Research Fellow at the Australian Centre for Advanced Photovoltaics at UNSW, with the new perovskite cell. Credit: Rob Largent/UNSW

They’re flexible, cheap to produce and simple to make – which is why perovskites are the hottest new material in solar cell design. And now, engineers at Australia’s University of New South Wales in Sydney have smashed the trendy new compound’s world efficiency record.

Speaking at the Asia-Pacific Solar Research Conference in Canberra on Friday 2 December, Anita Ho-Baillie, a Senior Research Fellow at the Australian Centre for Advanced Photovoltaics (ACAP), announced that her team at UNSW has achieved the highest efficiency rating with the largest perovskite solar cells to date.

The 12.1% efficiency rating was for a 16 cm2 perovskite solar cell, the largest single perovskite photovoltaic cell certified with the highest energy conversion efficiency, and was independently confirmed by the international testing centre Newport Corp, in Bozeman, Montana.
The new cell is at least 10 times bigger than the current certified high-efficiency perovskite solar cells on record.

Her team has also achieved an 18% efficiency rating on a 1.2 cm2 single perovskite cell, and an 11.5% for a 16 cm2 four-cell perovskite mini-module, both independently certified by Newport.

“This is a very hot area of research, with many teams competing to advance photovoltaic design,” said Ho-Baillie. “Perovskites came out of nowhere in 2009, with an efficiency rating of 3.8%, and have since grown in leaps and bounds.

These results place UNSW amongst the best groups in the world producing state-of-the-art high-performance perovskite solar cells. And I think we can get to 24% within a year or so.”


Perovskite is a structured compound, where a hybrid organic-inorganic lead or tin halide-based material acts as the light-harvesting active layer. They are the fastest-advancing solar technology to date, and are attractive because the compound is cheap to produce and simple to manufacture, and can even be sprayed onto surfaces.

“The versatility of solution deposition of perovskite makes it possible to spray-coat, print or paint on solar cells,” said Ho-Baillie. “The diversity of chemical compositions also allows cells be transparent, or made of different colours. Imagine being able to cover every surface of buildings, devices and cars with solar cells.”

Most of the world’s commercial solar cells are made from a refined, highly purified silicon crystal and, like the most efficient commercial silicon cells (known as PERC cells and invented at UNSW), need to be baked above 800?C in multiple high-temperature steps.

Perovskites, on the other hand, are made at low temperatures and 200 times thinner than silicon cells.

But although perovskites hold much promise for cost-effective solar energy, they are currently prone to fluctuating temperatures and moisture, making them last only a few months without protection. Along with every other team in the world, Ho-Baillie’s is trying to extend its durability.

Thanks to what engineers learned from more than 40 years of work with layered silicon, they’re are confident they can extend this.

 

Nevertheless, there are many existing applications where even disposable low-cost, high-efficiency solar cells could be attractive, such as use in disaster response, device charging and lighting in electricity-poor regions of the world.
Perovskite solar cells also have the highest power to weight ratio amongst viable photovoltaic technologies.

“We will capitalise on the advantages of perovskites and continue to tackle issues important for commercialisation, like scaling to larger areas and improving cell durability,” said Martin Green, Director of the ACAP and Ho-Baillie’s mentor. The project’s goal is to lift perovskite solar cell efficiency to 26%.

The research is part of a collaboration backed by $3.6 million in funding through the Australian Renewable Energy Agency’s (ARENA) ‘solar excellence’ initiative. ARENA’s CEO Ivor Frischknecht said the achievement demonstrated the importance of supporting early stage renewable energy technologies:
“In the future, this world-leading R&D could deliver efficiency wins for households and businesses through rooftop solar as well as for big solar projects like those being advanced through ARENA’s investment in large-scale solar.”

To make a perovskite solar cells, engineers grow crystals into a structure known as ‘perovskite’, named after Lev Perovski, the Russian mineralogist who discovered it. They first dissolve a selection of compounds in a liquid to make the ‘ink’, then deposit this on a specialised glass which can conduct electricity. When the ink dries, it leaves behind a thin film that crystallises on top of the glass when mild heat is applied, resulting in a thin layer of perovskite crystals.

The tricky part is growing a thin film of perovskite crystals so the resulting solar cell absorbs a maximum amount of light.

Worldwide, engineers are working to create smooth and regular layers of perovskite with large crystal grain sizes in order to increase photovoltaic yields.

Ho-Baillie, who obtained her PhD at UNSW in 2004, is a former chief engineer for Solar Sailor, an Australian company which integrates solar cells into purpose-designed commercial marine ferries which currently ply waterways in Sydney, Shanghai and Hong Kong.

New way to make low-cost perovskite solar cell technology


 

efficiently-photo-charging-lithium-ion-batteries-by-perovskite-solar-cell“By combining these two cells, the perovskite cell and the silicon cell, we are able to make much better use of the solar energy and achieve higher efficiencies than either cell on its own.”

Researchers at The Australian National University (ANU) have found a new way to fabricate high efficiency semi-transparent perovskite solar cells in a breakthrough that could lead to more efficient and cheaper solar electricity (Advanced Energy Materials, “Efficient Indium-Doped TiOxElectron Transport Layers for High-Performance Perovskite Solar Cells and Perovskite-Silicon Tandems”).

 

Dr Tom White from the ANU Research School of Engineering said the new fabrication method significantly improved the performance of perovskite solar cells, which can combine with conventional silicon solar cells to produce more efficient solar electricity.

 

ANU Ph.D. student The Duong, Dr.Tom White and Ph.D. student Jun Peng
 

ANU Ph.D. student The Duong, Dr.Tom White and Ph.D. student Jun Peng.

 

He said perovskite solar cells were extremely good at making electricity from visible light – blue, green and red – while conventional silicon solar cells were more efficient at converting infrared light into electricity.

“The prospect of adding a few additional processing steps at the end of a silicon cell production line to make perovskite cells is very exciting and could boost solar efficiency from 25 per cent to 30 per cent,” Dr White said.
“By combining these two cells, the perovskite cell and the silicon cell, we are able to make much better use of the solar energy and achieve higher efficiencies than either cell on its own.”
While perovskite cells can improve efficiency, they are not yet stable enough to be used on rooftops. Dr White said the new fabrication technique could help develop more reliable perovskite cells.
The new fabrication method involves adding a small amount of the element indium into one of the cell layers during fabrication. That could increase the cell’s power output by as much as 25 per cent.
“We have been able to achieve a record efficiency of 16.6 per cent for a semi-transparent perovskite cell, and 24.5 per cent for a perovskite-silicon tandem, which is one of the highest efficiencies reported for this type of cell,” said Dr White.
Dr White said the research placed ANU in a small group of labs around the world with the capability to improve silicon solar cell efficiency using perovskites.
The development builds on the state-of-the-art silicon cell research at ANU and is part of a $12.2 million “High-efficiency silicon/perovskite solar cells” project led by University of New South Wales and supported by $3.6 million of funding from the Australian Renewable Energy Agency.
Research partners include Monash University, Arizona State University, Suntech R&D Australia Pty Ltd and Trina Solar.
Source: The Australian National University

University of Waterloo: Opening Access to Energy: 4 Interconnected Research Areas Helping to Power a Global Revolution (with Videos)


E5_UWaterlooTHE WATERLOO RESEARCHERS HELPING POWER A GLOBAL REVOLUTION

There is no magic bullet, no single solution that will address the massive global energy inequities that leave billions of people with little or no access to electricity. Instead, change will come from connecting the ideas, innovations and experience of some of the world’s top minds.

Affordable Energy for Humanity (AE4H) focuses on four broad areas of research with the greatest opportunity to create meaningful, sustainable energy change.

RESEARCH AREA 1

Generation, Devices And Advanced Materials

Promise and potential: Next-generation batteries

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Next-generation batteries are an emerging market with unlimited potential — and Waterloo chemistry professor Linda Nazar is eager to see her team’s extraordinary labours pay off.

Nazar, who was recently named an Officer of the Order of Canada for her advancements in battery systems and clean-energy storage, is contributing to breakthroughs in the design of rechargeable batteries for grid storage, electric vehicles and other clean-energy technology.

“Our research team and others at the University of Waterloo are working on a lot of different battery technologies where we’re starting to see the hard efforts that we’ve put in over the last decade really paying off in terms of making batteries that have higher energy density, that are safer and also have longer cycle life,” says Nazar, who along with colleagues at the Waterloo Institute for Nanotechnology, Zhongwei Chen and Michel Pope, are planning to launch an Electrochemical Energy Research Centre at the University.

Their work could have huge ramifications for energy-poor developing countries.

“In impoverished countries where there’s an abundance of sunshine, it’s critical to be able to store renewable energy in affordable energy storage systems to allow for load leveling and also for storage at night or even off-season storage,” Nazar says.

“That allows communities that are limited in their electrical resources to have a cheap, abundant source of energy to power activity in the evening and when the sun isn’t shining.”

RESEARCH AREA 2

Information And Communication Technologies
For Energy System Convergence

Reducing the carbon footprint, improving energy efficiency

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Energy poverty is one of the biggest challenges facing humanity, according to Waterloo computer science professor Srinivasan Keshav.

“More than one billion around the world don’t have access to good forms of energy,” Keshav says. “The only energy they have is their own human labour, so if they want to dig a trench they have to do it by hand. How much firewood they can carry determines what they’re going to cook. That’s really what it comes down to.”

Keshav and his research team are focusing on greener, more efficient sources of energy that will ultimately help address these inequities.

“The work I’m doing in this lab is focused on two things,” Keshav explains. “One is to reduce the carbon footprint. The other is to improve the energy efficiency of systems that generate, transmit and consume energy — everything from power plants to the solar panels on your roof.

“Solar efficiency is going up and the costs are coming down at the same rate as costs have gone down for electronics. The same thing is happening with lighting. The technology is now coming into place which allows us to put a panel on the roof, [add] storage and efficient lighting — and you have the ability to transform lives.

“At some level the changes come not just from technology but from policy, not from research but from imagination. We make it possible for somebody to imagine a different future — and that perhaps is the biggest thing we do.”

A smart grid for smarter energy

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Just as smartphone technology has come to dominate the way we communicate, the future of 21st-century electricity may well belong to the smart grid.

The smart grid is an intelligent infrastructure that uses information technology — sensors, communications, automation and computers — to improve the way electricity is delivered. It also allows for renewables such as wind and solar power to be part of the equation.

“A lot of people do not have access to the electrical grid the way we do,” says Catherine Rosenberg, a professor of engineering and Canada Research Chair in the Future Internet at Waterloo. “There are two types of technologies that can have a major impact on the smart grid. The first technology is renewables — solar, wind. The second is energy storage.”

Rosenberg, who is collaborating with computer science professor Srinivasan Keshav, says that having access to renewable energy — solar panels, for example — and some storage would allow communities without grid access or with poor grid access to be self-sufficient.

Just as importantly, access must be affordable, and Rosenberg is optimistic that storage will become cost-efficient in the near future.

“Because there are more and more needs for energy storage— for example for electric vehicles — the price of energy storage is going to decrease,” she says. “We are in the business of designing systems by integrating many technologies and showing how those systems should be operated in a cost-efficient manner.”

fourth-ir-051416-aaeaaqaaaaaaaatfaaaajgezy2e0nwvilwu4ogitndzkzi1hymzilta1yty1nzczngqznaAlso Read: Nanotechnology and the ‘Fourth Industrial Revolution’: Solving Our Biggest Challenges with the Smallest of Things

RESEARCH AREA 3

Environmental and Human Dimensions Of Energy Transitions

Energy and sustainability: Lessons from the North

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Energy poverty is not confined to the developing world. There are nearly 300 remote communities across northern Canada — about 170 of them First Nations — and most rely on diesel generators with fuel flown in or trucked in via ice road.

It’s not only environmentally damaging, it’s also incredibly expensive — up to $1 per kilowatt hour — so building capacity to get energy from renewable sources is the preferred option. Renewable Energy Pix

“In our First Nations communities, we see both huge need and huge opportunity,” says Paul Parker, a professor in the Faculty of Environment. “We are here to work with communities to achieve what they want. The first question is, ‘What future do you want?’ And then it’s, ‘How do we design, evaluate and implement it?’

“The University of Waterloo is probably most famous for its technical capacity, but we also realize that technical capacity needs to have social context. We need the social scientists to work with our engineers and technicians in the North. Our students are fantastic. We’ve trained economic developers for communities across the North where they look and they see an opportunity and they say, ‘Let’s take those solutions to as many communities as possible,’ ” Parker says.

“We already have the technology to make these things happen, so [it’s about] the implementation. And what we are learning in Canada has [global implications] in other parts of the world that experience energy poverty.” 

wef-end-of-an-era-jm0hpnwopjfmrubpbirem_j4cbxunbwppi2pn_zjn1aAlso Read: WEF: Are We at the End of an Economic Era? Smart Decisions for a Changing World: What’s Next

RESEARCH AREA 4

Mirogrids For Dispersed Power

Microgrids and the power of decentralization

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As flaws in centralized power grids become apparent — their vulnerability to disruption and dependence on planet-warming fossil fuels — the time has come for renewable energy microgrids to take centre stage.

“Here at Waterloo we have a lot of expertise to provide in microgrids, not only to Canada but to the world, from simulation and modelling to hardware and social interactions withcommunities,” says Claudio Cañizares, a professor of electrical and computer engineering at Waterloo.

Scientists are trying to transform microgrids — which can operate independently or in conjunction with main power grids — into renewable energy-based systems by introducing solar and wind power. Challenges being addressed by research at Waterloo include making the systems economically feasible, and learning to manage the variability inherent to renewable energy sources like wind and solar. Cañizares and his fellow researchers are doing both theoretical work — simulation, modeling, optimization — and applied science so they can understand how the controls work in different environments.

“One of the main motivations for our work here is to try to improve or facilitate the introduction of these renewable sources and to move away from diesel in the remote, mostly indigenous, communities in Canada,” Cañizares says.

Ultimately, Cañizares believes the impact of affordable energy access will change lives.

His research partners in northern Chile, for example, are seeing young people who had left their communities return once affordable energy sources are introduced, and business opportunities cropping up that didn’t exist before.

“We have come a long way,” he says. “We believe Waterloo is particularly well-positioned … people are paying attention.”


Video: Matt Regehr and Light Imaging


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MIT: New solar cell is more efficient, costs less than its counterparts – new photovoltaic cell harvests more of sun’s energy. 


A silicon solar cell with silicon-germanium filter using a step-cell design (large) and a gallium arsenide phosphide layer on silicon step-cell proof-of-concept solar cell (small).Photo: Tahra Al Hammadi/Masdar Institute News.

The cost of solar power is beginning to reach price parity with cheaper fossil fuel-based electricity in many parts of the world, yet the clean energy source still accounts for just slightly more than 1 percent of the world’s electricity mix.

Solar, or photovoltaic (PV), cells, which convert sunlight into electrical energy, have a large role to play in boosting solar power generation globally, but researchers still face limitations to scaling up this technology. For example, developing very high-efficiency solar cells that can convert a significant amount of sunlight into usable electrical energy at very low costs remains a significant challenge.

A team of researchers from MIT and the Masdar Institute of Science and Technology may have found a way around this seemingly intractable tradeoff between efficiency and cost. The team has developed a new solar cell that combines two different layers of sunlight-absorbing material to harvest a broader range of the sun’s energy.
The researchers call the device a “step cell,” because the two layers are arranged in a stepwise fashion, with the lower layer jutting out beneath the upper layer, in order to expose both layers to incoming sunlight. Such layered, or “multijunction,” solar cells are typically expensive to manufacture, but the researchers also used a novel, low-cost manufacturing process for their step cell.

The team’s step-cell concept can reach theoretical efficiencies above 40 percent and estimated practical efficiencies of 35 percent, prompting the team’s principal investigators — Masdar Institute’s Ammar Nayfeh, associate professor of electrical engineering and computer science, and MIT’s Eugene Fitzgerald, the Merton C. Flemings-SMA Professor of Materials Science and Engineering — to plan a startup company to commercialize the promising solar cell.

Fitzgerald, who has launched several startups, including AmberWave Systems Corporation, Paradigm Research LLC, and 4Power LLC, thinks the step cells might be ready for the PV market within the next year or two.

The team presented its initial proof-of-concept step cell in June at the 43rd IEEE Photovoltaic Specialists Conference in Portland, Oregon. The researchers have also reported their findings at the 40th and 42nd annual conferences, and in the Journal of Applied Physics and IEEE Journal of Photovoltaics.

Beyond silicon

Traditional silicon crystalline solar cells, which have been touted as the industry’s gold standard in terms of efficiency for over a decade, are relatively cheap to manufacture, but they are not very efficient at converting sunlight into electricity. On average, solar panels made from silicon-based solar cells convert between 15 and 20 percent of the sun’s energy into usable electricity.

Silicon’s low sunlight-to-electrical energy efficiency is partially due to a property known as its bandgap, which prevents the semiconductor from efficiently converting higher-energy photons, such as those emitted by blue, green, and yellow light waves, into electrical energy. Instead, only the lower-energy photons, such as those emitted by the longer red light waves, are efficiently converted into electricity.

To harness more of the sun’s higher-energy photons, scientists have explored different semiconductor materials, such as gallium arsenide and gallium phosphide. While these semiconductors have reached higher efficiencies than silicon, the highest-efficiency solar cells have been made by layering different semiconductor materials on top of each other and fine-tuning them so that each can absorb a different slice of the electromagnetic spectrum.

These layered solar cells can reach theoretical efficiencies upward of 50 percent, but their very high manufacturing costs have relegated their use to niche applications, such as on satellites, where high costs are less important than low weight and high efficiency.

The Masdar Institute-MIT step cell, in contrast, can be manufactured at a fraction of the cost because a key component is fabricated on a substrate that can be reused. The device may thus help boost commercial applications of high-efficiency, multijunction solar cells at the industrial level.

Steps to success

The step cell is made by layering a gallium arsenide phosphide-based solar cell, consisting of a semiconductor material that absorbs and efficiently converts higher-energy photons, on a low-cost silicon solar cell.

The silicon layer is exposed, appearing like a bottom step. This intentional step design allows the top gallium arsenide phosphide (GaAsP) layer to absorb the high-energy photons (from blue, green, and yellow light) leaving the bottom silicon layer free to absorb lower-energy photons (from red light) not only transmitted through top layers but also from the entire visible light spectrum.

“We realized that when the top gallium arsenide phosphide layer completely covered the bottom silicon layer, the lower-energy photons were absorbed by the silicon germanium — the substrate on which the gallium arsenide phosphide is grown — and thus the solar cell had a much lower efficiency,” explains Sabina Abdul Hadi, a PhD student at Masdar Institute whose doctoral dissertation provided the foundational research for the step-cell. “By etching away the top layer and exposing some of the silicon layer, we were able to increase the efficiency considerably.”

Working under Nayfeh’s supervision, Abdul Hadi conducted simulations based on experimental results to determine the optimal levels and geometrical configuration of the GaAsP layer on silicon to yield the highest efficiencies. Her findings resulted in the team’s initial proof-of-concept solar cell. Abdul Hadi will continue supporting the step cell’s technological development as a post-doctoral researcher at Masdar Institute.

On the MIT side, the team developed the GaAsP, which they did by growing the semiconductor alloy on a substrate made of silicon germanium (SiGe).

“Gallium arsenide phosphide cannot be grown directly on silicon, because its crystal lattices differ considerably from silicon’s, so the silicon crystals become degraded. That’s why we grew the gallium arsenide phosphide on the silicon germanium — it provides a more stable base,” explains Nayfeh.

The problem with the silicon germanium under the GaAsP layer is that SiGe absorbs the lower-energy light waves before it reaches the bottom silicon layer, and SiGe does not convert these low-energy light waves into current.

“To get around the optical problem posed by the silicon germanium, we developed the idea of the step cell, which allows us to leverage the different energy absorption bands of gallium arsenide phosphate and silicon,” says Nayfeh.

The step cell concept led to an improved cell in which the SiGe template is removed and re-used, creating a solar cell in which GaAsP cell tiles are directly on top of a silicon cell. The step-cell allows for SiGe reuse since the GaAsP cell tiles can be under-cut during the transfer process. Explaining the future low-cost fabrication process, Fitzgerald says: “We grew the gallium arsenide phosphide on top of the silicon germanium, patterned it in the optimized geometric configuration, and bonded it to a silicon cell. Then we etched through the patterned channels and lifted off the silicon germanium alloys on silicon. What remains then, is a high-efficiency tandem solar cell and a silicon germanium template, ready to be reused.”

Because the tandem cell is bonded together, rather than created as a monolithic solar cell (where all layers are grown onto a single substrate), the SiGe can be removed and reused repeatedly, which significantly reduces the manufacturing costs.

“Adding that one layer of the gallium arsenide phosphide can really boost efficiency of the solar cell but because of the unique ability to etch away the silicon germanium and reuse it, the cost is kept low because you can amortize that silicon germanium cost over the course of manufacturing many cells,” Fitzgerald adds.

Filling a market gap

Fitzgerald believes the step cell fits well in the existing gap of the solar PV market, between the super high-efficiency and low-efficiency industrial applications. And as volume increases in this market gap, the manufacturing costs should be driven down even further over time.

This project began as one of nine Masdar Institute-MIT Flagship Research Projects, which are high-potential projects involving faculty and students from both universities. The MIT and Masdar Institute Cooperative Program helped launch the Masdar Institute in 2007. Research collaborations between the two institutes address global energy and sustainability issues, and seek to develop research and development capabilities in Abu Dhabi.

“This research project highlights the valuable role that research and international collaboration plays in developing a commercially-relevant technology-based innovation, and it is a perfect demonstration of how a research idea can transform into an entrepreneurial reality,” says Nayfeh.

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How can we store solar energy for periods when the sun doesn’t shine? Researchers Turn to Known – Effective – Low Cost Method with a “Twist”


Solar Storage 082516 id44316

How can we store solar energy for period when the sun doesn’t shine?

 

One solution is to convert it into hydrogen through water electrolysis. The idea is to use the electrical current produced by a solar panel to ‘split’ water molecules into hydrogen and oxygen. Clean hydrogen can then be stored away for future use to produce electricity on demand, or even as a fuel.

 
But this is where things get complicated. Even though different hydrogen-production technologies have given us promising results in the lab, they are still too unstable or expensive and need to be further developed to use on a commercial and large scale.
The approach taken by EPFL and CSEM researchers is to combine components that have already proven effective in industry in order to develop a robust and effective system. Their prototype is made up of three interconnected, new-generation, crystalline silicon solar cells attached to an electrolysis system that does not rely on rare metals.

The device is able to convert solar energy into hydrogen at a rate of 14.2%, and has already been run for more than 100 hours straight under test conditions. In terms of performance, this is a world record for silicon solar cells and for hydrogen production without using rare metals. It also offers a high level of stability.

Solar Storage 082516 id44316
The device is able to convert solar energy into hydrogen at a rate of 14.2 percent, and has already been run for more than 100 hours straight. (Image: Infini Lab / EPFL)
Enough to power a fuel cell car over 10,000km every year

An Effective and Low-Cost Solution for Storing Solar Energy

 

The method, which surpasses previous efforts in terms of stability, performance, lifespan and cost efficiency, is published in the Journal of The Electrochemical Society (“Solar-to-Hydrogen Production at 14.2% Efficiency with Silicon Photovoltaics and Earth-Abundant Electrocatalysts”). “A 12-14 m2 system installed in Switzerland would allow the generation and storage of enough hydrogen to power a fuel cell car over 10,000 km every year”, says Christophe Ballif, who co-authored the paper.

 
High voltage cells have an edge

 
The key here is making the most of existing components, and using a ‘hybrid’ type of crystalline-silicon solar cell based on hetero-junction technology. The researchers’ sandwich structure – using layers of crystalline silicon and amorphous silicon – allows for higher voltages. And this means that just three of these cells, interconnected, can already generate an almost ideal voltage for electrolysis to occur. The electro-chemical part of the process requires a catalyst made from nickel, which is widely available.

 
“With conventional crystalline silicon cells, we would have to link up four cells to get the same voltage,” says co-author Miguel Modestino at EPFL.”So that’s the strength of this method.”

 
A stable and economically viable method 

hydrogen-earth-150x150
The new system is unique when it comes to cost, performance and lifespan. “We wanted to develop a high performance system that can work under current conditions,” says Jan-Willem Schüttauf, a researcher at CSEM and co-author of the paper. “The hetero-junction cells that we use belong to the family of crystalline silicon cells, which alone account for about 90% of the solar panel market. It is a well-known and robust technology whose lifespan exceeds 25 years.

And it also happens to cover the south side of the CSEM building in Neuchâtel.”
The researchers used standard hetero-junction cells to prove the concept; by using the best cells of that type, they would expect to achieve a performance above 16%.

 
Source: Ecole Polytechnique Fédérale de Lausanne