Solar Cell Solutions to Industry’s Biggest Hurdle – Degradation – UCLA Samueli School of Engineering

Materials scientists at the UCLA Samueli School of Engineering and colleagues from five other universities around the world have discovered the major reason why perovskite solar cells — which show great promise for improved energy-conversion efficiency — degrade in sunlight, causing their performance to suffer over time.  

The team successfully demonstrated a simple manufacturing adjustment to fix the cause of the degradation, clearing the biggest hurdle toward the widespread adoption of the thin-film solar cell technology. 

  

A research paper detailing the findings was published in Nature. The research is led by Yang Yang, a UCLA Samueli professor of materials science and engineering and holder of the Carol and Lawrence E. Tannas, Jr., Endowed Chair. The co-first authors are Shaun Tan and Tianyi Huang, both recent UCLA Samueli Ph.D. graduates whom Yang advised. 

Perovskites are a group of materials that have the same atomic arrangement or crystal structure as the mineral calcium titanium oxide. A subgroup of perovskites, metal halide perovskites, are of great research interest because of their promising application for energy-efficient, thin-film solar cells.  

 

Perovskite-based solar cells could be manufactured at much lower costs than their silicon-based counterparts, making solar energy technologies more accessible if the commonly known degradation under long exposure to illumination can be properly addressed. For further information see the IDTechEx report on Energy Harvesting Microwatt to Gigawatt: Opportunities 2020-2040. 

   

“Perovskite-based solar cells tend to deteriorate in sunlight much faster than their silicon counterparts, so their effectiveness in converting sunlight to electricity drops over the long term,” said Yang, who is also a member of the California NanoSystems Institute at UCLA. “However, our research shows why this happens and provides a simple fix. This represents a major breakthrough in bringing perovskite technology to commercialization and widespread adoption.” 

  

A common surface treatment used to remove solar cell defects involves depositing a layer of organic ions that makes the surface too negatively charged. The UCLA-led team found that while the treatment is intended to improve energy-conversion efficiency during the fabrication process of perovskite solar cells, it also unintentionally creates a more electron-rich surface — a potential trap for energy-carrying electrons. 

  

This condition destabilizes the orderly arrangement of atoms, and over time the perovskite solar cells become increasingly less efficient, ultimately making them unattractive for commercialization. 

  

Armed with this new discovery, the researchers found a way to address the cells’ long-term degradation by pairing the positively charged ions with negatively charged ones for surface treatments. The switch enables the surface to be more electron-neutral and stable, while preserving the integrity of the defect-prevention surface treatments. 

  

 The team tested the endurance of their solar cells in a lab under accelerated ageing conditions and 24/7 illumination designed to mimic sunlight. The cells managed to retain 87% of their original sunlight-to-electricity conversion performance for more than 2,000 hours. For comparison, solar cells manufactured without the fix dropped to 65% of their original performance after testing over the same time and conditions. 

  

“Our perovskite solar cells are among the most stable in efficiency reported to date,” Tan said. “At the same time, we’ve also laid new foundational knowledge, on which the community can further develop and refine our versatile technique to design even more stable perovskite solar cells.” 

  

Source and top image: University of California Los Angeles 

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Enhancing quantum dot solar cell efficiency to 11.53%

Figure 1. Shown above is the structure of CQDSC and the optical redistribution profiles of devices by TMF optical simulation. Credit: Professor Sung-Yeon Jang, UNIST

A novel technology that can improve the efficiency of quantum dot solar cells to 11.53% has been unveiled. Published in the February 2020 issue of Advanced Energy Materials, it has been evaluated as a study that solved the challenges posed by the generation of electric currents from sunlight by solar cells by enhancing the hole extraction.

A research team, led by Professor Sung-Yeon Jang in the School of Energy and Chemical Engineering at UNIST has developed a photovoltaic device that maximizes the performance of quantum dot solar cells by using organic polymers.

Solar cells use a characteristic of which electrons and holes are generated in the absorber layer. The free free electrons and hole then move through the cell, creating and filling in holes. It is this movement of electrons and holes that generate electricity. Therefore, creating multiple electron-hole pairs and transporting them are an important consideration in the design of efficient solar cells.

The research team switched one side of the quantum dot solar cells to organic hole transport materials (HTMs) to better extract and transport holes. This is because the newly-developed organic polymer not only possesses superior hole extracting ability, but also prevents electrons and holes from recombining, which allow efficient transport of holes to the anode.

Generally, quantum dot solar cells combine electron-rich quantum dots (n-type CQDs) and hole-rich quantum dots (p-type QDs). In this work, the research team developed organic π‐conjugated polymer (π‐CP) based HTMs, which can achieve performance superior to that of state‐of‐the‐art HTM, p‐type CQDs. The molecular engineering of the π‐CPs alters their optoelectronic properties, and the charge generation and collection in colloidal quantum dot solar cells (CQDSCs), using them are substantially improved.

As a result, the research team succeeded in achieving power conversion efficiency (PCE) of 11.53% with decent air‐storage stability. This is the highest reported PCE among CQDSCs using organic HTMs, and even higher than the reported best solid‐state ligand exchange‐free CQDSC using pCQD‐HTM. “From the viewpoint of device processing, device fabrication does not require any solid‐state ligand exchange step or layer‐by‐layer deposition process, which is favorable for exploiting commercial processing techniques,” noted the research team.

“This study solves the problem of hole transport, which has been the major obstacle for the genration of electric currents in quantum dot solar cells,” says Professor Jang. “This work suggests that the molecular engineering of organic π‐CPs is an efficient strategy for simultaneous improvement in PCE and processability of CQDSCs, and additional optimization might further improve their performance.”

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Explore further

Light on efficiency loss in organic solar cells

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More information: Muhibullah Al Mubarok et al. Molecular Engineering in Hole Transport π‐Conjugated Polymers to Enable High Efficiency Colloidal Quantum Dot Solar Cells, Advanced Energy Materials (2020). DOI: 10.1002/aenm.201902933

Journal information: Advanced Energy Materials

Provided by Ulsan National Institute of Science and Technology

Super Secret Perovskite Solar Cell Company Bursts Out Of Stealth Mode

HPT has collaborated with NREL on perovskite ink for solar cells, like this one developed by NREL researcher David Moore (Photo by Dennis Schroeder, NREL).

For the past six years, a major US oil and gas holding company has been collaborating with the National Renewable Energy Lab on new breakthrough perovskite solar cell research. What a twist!

The effort has been conducted through a relatively new division of the firm and it hasn’t attracted much attention, except that earlier this month they finally let something slip on the newswires and now the cat’s out of the bag.

Oil Company Hearts Perovskite Solar Cells

The holding company in question is Hunt Consolidated, Inc., parent of the 80-year-old privately held global oil and gas leader Hunt Oil and of a somewhat lesser known entity called Hunt Perovskite Technologies.

So, why has a major fossil fuel company been collaborating with NREL on cutting edge research leading to the next generation of low cost solar cells?

After all, other global oil and gas stakeholders are venturing into renewable energy. However, they are mainly focused on market-proven technologies that don’t disrupt their fossil fuel business, at least not for the time being.

Hunt’s new perovskite research is a whole ‘nother kettle of fish. It could have a profound, widespread impact on the energy marketplace and accelerate the transition from fossil fuels to renewables.

That’s because perovskite technology can push down solar costs far below today’s costs. Perovskite solar cells are also lighter and more flexible, which means they have a greater range of application.

For a bonus, perovskite solar cells can be “printed” with a relatively conventional high-volume manufacturing process.

Perovskite solar cells are only just beginning to edge out of the laboratory, now that researchers have finally worked out the kinks. Once they hit the shelves, they will kick the global solar market into a whole new level of activity.

As for why Hunt, last week Forbestook a crack at the mystery and noted that the current head of the family business, Hunter L. Hunt, spent the past 10 years creating and then spinning off a new high voltage power line company.

That venture, along with the company’s investment arm Hunt Energy Enterprises, indicates that Hunt Oil is looking more holistically at new high tech opportunities in the energy market aside from just digging up stuff out of the ground.

More & Better Perovskite Solar Cells

The main challenge with perovskite as a solar cell material is durability, and researchers have been trying various formulas to improve durability without sacrificing too much solar conversion efficiency.

Hunt Perovskite Technologies launched in 2013 with a focus on the perovskite durability problem, as a corporate partner of NREL.

The work came to fruit late last year, when Hunt was able to demonstrate an ink-based manufacturing process for its new solar cell, to the satisfaction of the International Electrotechnical Commission. According to Hunt, the new solar cell exceeds IEC standards for temperature, humidity, white light and ultraviolet stress while achieving a fairly impressive solar conversion efficiency of 18%.

Legacy companies like Hunt are not going to shed their fossil fuel interests willy-nilly, but in a press statement Hunter Hunt indicated that his family business is prepping for change.

“We strategically chose to develop perovskite solar several years ago; we envisioned its strategic importance as an innovative new energy technology in addressing the world’s energy needs for the future, as well playing a part in combating climate change,” he said.  “As part of the global energy transition that is occurring, our solar team is hoping to make a meaningful contribution.”

MIT – Researchers develop a roadmap for growth of new solar cells – Could become Competitive with Silicon

Perovskites, a family of materials defined by a particular kind of molecular structure as illustrated here, have great potential for new kinds of solar cells. A new study from MIT shows how these materials could gain a foothold in the solar marketplace. Image: Christine Daniloff, MIT

Starting with higher-value niche markets and then expanding could help perovskite-based solar panels become competitive with silicon

Materials called perovskites show strong potential for a new generation of solar cells, but they’ve had trouble gaining traction in a market dominated by silicon-based solar cells. Now, a study by researchers at MIT and elsewhere outlines a roadmap for how this promising technology could move from the laboratory to a significant place in the global solar market.

The “technoeconomic” analysis shows that by starting with higher-value niche markets and gradually expanding, solar panel manufacturers could avoid the very steep initial capital costs that would be required to make perovskite-based panels directly competitive with silicon for large utility-scale installations at the outset. Rather than making a prohibitively expensive initial investment, of hundreds of millions or even billions of dollars, to build a plant for utility-scale production, the team found that starting with more specialized applications could be accomplished for more realistic initial capital investment on the order of $40 million.

The results are described in a paper in the journal Joule by MIT postdoc Ian Mathews, research scientist Marius Peters, professor of mechanical engineering Tonio Buonassisi, and five others at MIT, Wellesley College, and Swift Solar Inc.

Solar cells based on perovskites — a broad category of compounds characterized by a certain arrangement of their molecular structure — could provide dramatic improvements in solar installations. Their constituent materials are inexpensive, and they could be manufactured in a roll-to-roll process like printing a newspaper, and printed onto lightweight and flexible backing material. This could greatly reduce costs associated with transportation and installation, although they still require further work to improve their durability. Other promising new solar cell materials are also under development in labs around the world, but none has yet made inroads in the marketplace.

“There have been a lot of new solar cell materials and companies launched over the years,” says Mathews, “and yet, despite that, silicon remains the dominant material in the industry and has been for decades.”

Why is that the case? “People have always said that one of the things that holds new technologies back is that the expense of constructing large factories to actually produce these systems at scale is just too much,” he says. “It’s difficult for a startup to cross what’s called ‘the valley of death,’ to raise the tens of millions of dollars required to get to the scale where this technology might be profitable in the wider solar energy industry.”

But there are a variety of more specialized solar cell applications where the special qualities of perovskite-based solar cells, such as their light weight, flexibility, and potential for transparency, would provide a significant advantage, Mathews says. By focusing on these markets initially, a startup solar company could build up to scale gradually, leveraging the profits from the premium products to expand its production capabilities over time.

Describing the literature on perovskite-based solar cells being developed in various labs, he says, “They’re claiming very low costs. But they’re claiming it once your factory reaches a certain scale. And I thought, we’ve seen this before — people claim a new photovoltaic material is going to be cheaper than all the rest and better than all the rest. That’s great, except we need to have a plan as to how we actually get the material and the technology to scale.”

As a starting point, he says, “We took the approach that I haven’t really seen anyone else take: Let’s actually model the cost to manufacture these modules as a function of scale. So if you just have 10 people in a small factory, how much do you need to sell your solar panels at in order to be profitable? And once you reach scale, how cheap will your product become?”

The analysis confirmed that trying to leap directly into the marketplace for rooftop solar or utility-scale solar installations would require very large upfront capital investment, he says. But “we looked at the prices people might get in the internet of things, or the market in building-integrated photovoltaics. People usually pay a higher price in these markets because they’re more of a specialized product. They’ll pay a little more if your product is flexible or if the module fits into a building envelope.” Other potential niche markets include self-powered microelectronics devices.

Such applications would make the entry into the market feasible without needing massive capital investments. “If you do that, the amount you need to invest in your company is much, much less, on the order of a few million dollars instead of tens or hundreds of millions of dollars, and that allows you to more quickly develop a profitable company,” he says.

“It’s a way for them to prove their technology, both technically and by actually building and selling a product and making sure it survives in the field,” Mathews says, “and also, just to prove that you can manufacture at a certain price point.”

Already, there are a handful of startup companies working to try to bring perovskite solar cells to market, he points out, although none of them yet has an actual product for sale. The companies have taken different approaches, and some seem to be embarking on the kind of step-by-step growth approach outlined by this research, he says. “Probably the company that’s raised the most money is a company called Oxford PV, and they’re looking at tandem cells,” which incorporate both silicon and perovskite cells to improve overall efficiency. Another company is one started by Joel Jean PhD ’17 (who is also a co-author of this paper) and others, called Swift Solar, which is working on flexible perovskites. And there’s a company called Saule Technologies, working on printable perovskites.

Mathews says the kind of technoeconomic analysis the team used in its study could be applied to a wide variety of other new energy-related technologies, including rechargeable batteries and other storage systems, or other types of new solar cell materials.

“There are many scientific papers and academic studies that look at how much it will cost to manufacture a technology once it’s at scale,” he says. “But very few people actually look at how much does it cost at very small scale, and what are the factors affecting economies of scale? And I think that can be done for many technologies, and it would help us accelerate how we get innovations from lab to market.”

The research team also included MIT alumni Sarah Sofia PhD ’19 and Sin Cheng Siah PhD ’15, Wellesley College student Erica Ma, and former MIT postdoc Hannu Laine. The work was supported by the European Union’s Horizon 2020 research and innovation program, the Martin Family Society for Fellows of Sustainability, the U.S. Department of Energy, Shell, through the MIT Energy Initiative, and the Singapore-MIT Alliance for Research and Technology.

After 40 Years of Searching, Scientists Identify The Key Flaw in Solar Panel Efficiency

Solar panels are fantastic pieces of technology, but we need to work out how to make them even more efficient – and scientists just solved a 40-year-old mystery around one of the key obstacles to increased efficiency.

A new study outlines a material defect in silicon used to produce solar cells that has previously gone undetected. It could be responsible for the 2 percent efficiency drop that solar cells can see in the first hours of use: Light Induced Degradation (LID).

Multiplied by the increasing number of panels installed at solar farms around the world, that drop equals a significant cost in gigawatts that non-renewable energy sources have to make up for.

New Efficient Solar Panels Coming to the Market in 2019

In fact, the estimated loss in efficiency worldwide from LID is estimated to equate to more energy than can be generated by the UK’s 15 nuclear power plants. The new discovery could help scientists make up some of that shortfall.

“Because of the environmental and financial impact solar panel ‘efficiency degradation’ has been the topic of much scientific and engineering interest in the last four decades,” says one of the researchers, Tony Peaker from the University of Manchester in the UK.

“However, despite some of the best minds in the business working on it, the problem has steadfastly resisted resolution until now.”

To find what 270 research papers across four decades had previously been unable to determine, the latest study used an electrical and optical technique called deep-level transient spectroscopy (DLTS) to find weaknesses in the silicon.

Here’s what the DLTS analysis found: As the electronic charge in the solar cells gets transformed into sunlight, the flow of electrons gets trapped; in turn, that reduces the level of electrical power that can be produced.

This defect lies dormant until the solar panel gets heated, the team found.

“We’ve proved the defect exists, its now an engineering fix that is needed,” says one of the researchers, Iain Crowe from the University of Manchester.

The researchers also found that higher quality silicon had charge carriers (electrons which carry the photon energy) with a longer ‘lifetime’, which backs up the idea that these traps are linked to the efficiency degradation.

What’s more, heating the material in the dark, a process often used to remove traps from silicon, seems to reverse the degradation.

The work to push solar panel efficiency rates higher continues, with breakthroughs continuing to happen in the lab, and nature offering up plenty of efficiency tipsas well. Now that the Light Induced Degradation mystery has been solved, solar farms across the globe should benefit.

“An absolute drop of 2 percent in efficiency may not seem like a big deal, but when you consider that these solar panels are now responsible for delivering a large and exponentially growing fraction of the world’s total energy needs, it’s a significant loss of electricity generating capacity,” says Peaker.

The research has been published in the Journal of Applied Physics.

A Path to Cheaper Flexible Solar Cells -Researchers at Georgia IT and MIT are Developing the Potential Perovskite-Based Solar Cells

A researcher at Georgia Tech holds a perovskite-based solar cell, which is flexible and lighter than silicon-based versions. Credit: Rob Felt, Georgia Tech

There’s a lot to like about perovskite-based solar cells. They are simple and cheap to produce, offer flexibility that could unlock a wide new range of installation methods and places, and in recent years have reached energy efficiencies approaching those of traditional silicon-based cells.

But figuring out how to produce perovskite-based energy devices that last longer than a couple of months has been a challenge.

Now researchers from Georgia Institute of Technology, University of California San Diego and Massachusetts Institute of Technology have reported new findings about perovskite solar cells that could lead the way to devices that perform better.

“Perovskite solar cells offer a lot of potential advantages because they are extremely lightweight and can be made with flexible plastic substrates,” said Juan-Pablo Correa-Baena, an assistant professor in the Georgia Tech School of Materials Science and Engineering. “To be able to compete in the marketplace with silicon-based solar cells, however, they need to be more efficient.”

In a study that was published February 8 in the journal Science and was sponsored by the U.S Department Energy and the National Science Foundation, the researchers described in greater detail the mechanisms of how adding alkali metal to the traditional perovskites leads to better performance.

“Perovskites could really change the game in solar,” said David Fenning, a professor of nanoengineering at the University of California San Diego. “They have the potential to reduce costs without giving up performance. But there’s still a lot to learn fundamentally about these materials.”

To understand perovskite crystals, it’s helpful to think of its crystalline structure as a triad. One part of the triad is typically formed from the element lead. The second is typically made up of an organic component such as methylammonium, and the third is often comprised of other halides such as bromine and iodine.

In recent years, researchers have focused on testing different recipes to achieve better efficiencies, such as adding iodine and bromine to the lead component of the structure. Later, they tried substituting cesium and rubidium to the part of the perovskite typically occupied by organic molecules.

“We knew from earlier work that adding cesium and rubidium to a mixed bromine and iodine lead perovskite leads to better stability and higher performance,” Correa-Baena said.

But little was known about why adding those alkali metals improved performance of the perovskites.

To understand exactly why that seemed to work, the researchers used high-intensity X-ray mapping to examine the perovskites at the nanoscale.

“By looking at the composition within the perovskite material, we can see how each individual element plays a role in improving the performance of the device,” said Yanqi (Grace) Luo, a nanoengineering PhD student at UC San Diego.

They discovered that when the cesium and rubidium were added to the mixed bromine and iodine lead perovskite, it caused the bromine and iodine to mix together more homogeneously, resulting in up to 2 percent higher conversion efficiency than the materials without these additives.

“We found that uniformity in the chemistry and structure is what helps a perovskite solar cell operate at its fullest potential,” Fenning said. “Any heterogeneity in that backbone is like a weak link in the chain.”

Even so, the researchers also observed that while adding rubidium or cesium caused the bromine and iodine to become more homogenous, the halide metals themselves within their own cation remained fairly clustered, creating inactive “dead zones” in the solar cell that produce no current.

“This was surprising,” Fenning said. “Having these dead zones would typically kill a solar cell. In other materials, they act like black holes that suck in electrons from other regions and never let them go, so you lose current and voltage.

“But in these perovskites, we saw that the dead zones around rubidium and cesium weren’t too detrimental to solar cell performance, though there was some current loss,” Fenning said. “This shows how robust these materials are but also that there’s even more opportunity for improvement.”

The findings add to the understanding of how the perovskite-based devices work at the nanoscale and could lay the groundwork for future improvements.

“These materials promise to be very cost effective and high performing, which is pretty much what we need to make sure photovoltaic panels are deployed widely,” Correa-Baena said. “We want to try to offset issues of climate change, so the idea is to have photovoltaic cells that are as cheap as possible.”

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Materials provided by Georgia Institute of Technology. Note: Content may be edited for style and length.

MIT: Unleashing perovskites’ potential for solar cells

Solar cells made of perovskite have great promise, in part because they can easily be made on flexible substrates, like this experimental cell. Image: Ken Richardson

New results show how varying the recipe could bring these materials closer to commercialization.

Perovskites — a broad category of compounds that share a certain crystal structure — have attracted a great deal of attention as potential new solar-cell materials because of their low cost, flexibility, and relatively easy manufacturing process.

But much remains unknown about the details of their structure and the effects of substituting different metals or other elements within the material.

Conventional solar cells made of silicon must be processed at temperatures above 1,400 degrees Celsius, using expensive equipment that limits their potential for production scaleup.

In contrast, perovskites can be processed in a liquid solution at temperatures as low as 100 degrees, using inexpensive equipment. What’s more, perovskites can be deposited on a variety of substrates, including flexible plastics, enabling a variety of new uses that would be impossible with thicker, stiffer silicon wafers.

Now, researchers have been able to decipher a key aspect of the behavior of perovskites made with different formulations:

With certain additives there is a kind of “sweet spot” where greater amounts will enhance performance and beyond which further amounts begin to degrade it.

The findings are detailed this week in the journal Science, in a paper by former MIT postdoc Juan-Pablo Correa-Baena, MIT professors Tonio Buonassisi and Moungi Bawendi, and 18 others at MIT, the University of California at San Diego, and other institutions.

Perovskite solar cells are thought to have great potential, and new understanding of how changes in composition affect their behavior could help to make them practical. Image: Ken Richardson

Perovskites are a family of compounds that share a three-part crystal structure. Each part can be made from any of a number of different elements or compounds — leading to a very broad range of possible formulations. Buonassisi compares designing a new perovskite to ordering from a menu, picking one (or more) from each of column A, column B, and (by convention) column X.

“You can mix and match,” he says, but until now all the variations could only be studied by trial and error, since researchers had no basic understanding of what was going on in the material.

In previous research by a team from the Swiss École Polytechnique Fédérale de Lausanne, in which Correa-Baena participated, had found that adding certain alkali metals to the perovskite mix could improve the material’s efficiency at converting solar energy to electricity, from about 19 percent to about 22 percent.

But at the time there was no explanation for this improvement, and no understanding of exactly what these metals were doing inside the compound. “Very little was known about how the microstructure affects the performance,” Buonassisi says.

Now, detailed mapping using high-resolution synchrotron nano-X-ray fluorescence measurements, which can probe the material with a beam just one-thousandth the width of a hair, has revealed the details of the process, with potential clues for how to improve the material’s performance even further.

It turns out that adding these alkali metals, such as cesium or rubidium, to the perovskite compound helps some of the other constituents to mix together more smoothly. As the team describes it, these additives help to “homogenize” the mixture, making it conduct electricity more easily and thus improving its efficiency as a solar cell.

But, they found, that only works up to a certain point. Beyond a certain concentration, these added metals clump together, forming regions that interfere with the material’s conductivity and partly counteract the initial advantage. In between, for any given formulation of these complex compounds, is the sweet spot that provides the best performance, they found.

“It’s a big finding,” says Correa-Baena, who in January became an assistant professor of materials science and engineering at Georgia Tech.

What the researchers found, after about three years of work at MIT and with collaborators at UCSD, was “what happens when you add those alkali metals, and why the performance improves.” They were able to directly observe the changes in the composition of the material, and reveal, among other things, these countervailing effects of homogenizing and clumping.

“The idea is that, based on these findings, we now know we should be looking into similar systems, in terms of adding alkali metals or other metals,” or varying other parts of the recipe, Correa-Baena says.

While perovskites can have major benefits over conventional silicon solar cells, especially in terms of the low cost of setting up factories to produce them, they still require further work to boost their overall efficiency and improve their longevity, which lags significantly behind that of silicon cells.

Although the researchers have clarified the structural changes that take place in the perovskite material when adding different metals, and the resulting changes in performance, “we still don’t understand the chemistry behind this,” Correa-Baena says. That’s the subject of ongoing research by the team. The theoretical maximum efficiency of these perovskite solar cells is about 31 percent, according to Correa-Baena, and the best performance to date is around 23 percent, so there remains a significant margin for potential improvement.

Although it may take years for perovskites to realize their full potential, at least two companies are already in the process of setting up production lines, and they expect to begin selling their first modules within the next year or so. Some of these are small, transparent and colorful solar cells designed to be integrated into a building’s façade. “It’s already happening,” Correa-Baena says, “but there’s still work to do in making these more durable.”

Once issues of large-scale manufacturability, efficiency, and durability are addressed, Buonassisi says, perovskites could become a major player in the renewable energy industry. “If they succeed in making sustainable, high-efficiency modules while preserving the low cost of the manufacturing, that could be game-changing,” he says. “It could allow expansion of solar power much faster than we’ve seen.”

Perovskite solar cells “are now primary candidates for commercialization. Thus, providing deeper insights, as done in this work, contributes to future development,” says Michael Saliba, a senior researcher on the physics of soft matter at the University of Fribourg, Switzerland, who was not involved in this research.

Saliba adds, “This is great work that is shedding light on some of the most investigated materials. The use of synchrotron-based, novel techniques in combination with novel material engineering is of the highest quality, and is deserving of appearing in such a high-ranking journal.” He adds that work in this field “is rapidly progressing. Thus, having more detailed knowledge will be important for addressing future engineering challenges.”

The study, which included researchers at Purdue University and Argonne National Laboratory, in addition to those at MIT and UCSD, was supported by the U.S. Department of Energy, the National Science Foundation, the Skolkovo Institute of Science and Technology, and the California Energy Commission.

New Hybrid solar cells harness energy from … raindrops?

Renewable energy is the cleanest and inexhaustible source of energy. They are a great alternative to fossil fuels.

Renewable energy doesn’t emit any greenhouse gases in the environment. They are environment-friendly and help us tackle the most important concern of the 21st Century – Climate Change.

Solar is one of the most important forms of renewable energy. Sun is an inexhaustible source of energy and solar cells help capture that clean energy for both commercial and domestic purposes. Despite all these advantages, Solar cells are not efficient when it comes to producing energy during rainy seasons. Since the input energy gets reduced, solar cells become practically useless when rain clouds are overhead.

But what if we could overcome this problem?  What if we could actually generate energy from raindrops?

Scientists from the University of Soochow, China have overcome the design flaw of solar cells by allowing them to generate energy both in the sunny and rainy season.

This technology holds the potential of revolutionizing renewable energy completely.

The key part of this new Hybrid solar technology is the triboelectric nanogenerator or TENG. A device capable of producing an electric charge from the friction of two materials rubbing together.

How Hybrid solar cells work?

These new hybrid solar cells works using a material called Graphene. It has the ability to produce energy from raindrops.

Like any other solar panel, these hybrid solar cells also generate electricity during a normal sunny day using the current technology, but when cloud gathers and raindrop falls, this solar panels system switch to its graphene system.

Graphene, in its liquid form, can produce electricity due to the presence of delocalized electrons that help us create a pseudocapacitor framework. This pseudo framework helps us generate electricity.

When raindrops fall on hybrid solar panels, they get separated as positive ions and negative ions.

These positive ions are mainly salt-related ions, like sodium and calcium which accumulates on the surface of graphene. These positive ions interact with the loosely associated negative ions in graphene and create a system that acts like a pseudocapacitor.

The difference in potential between these ions produces current and voltage.

Although, it is important to mention that this is not a first attempt to invent all-weathered Solar panels. Earlier, researchers created a solar panel with triboelectric nanogenerator on top, an insulating layer in the middle and solar panel at the bottom. But this system possessed too much electrical resistance and sunlight was not able to reach the solar cells due to the opaque nature of insulators.

The newly designed hybrid solar panel is an efficient device, where the triboelectric nanogenerator and the solar panel share a common and transparent electrode. There are special grooves incorporated in the material which increases the efficiency of both raindrops and sunlight captured.

According to the researchers, the idea of special grooves was derived from commercial DVD’s. DVD’s come pre-etched with parallel grooves just hundreds of nanometer across. Designing the device with this grooves helps to boost the surface interaction of raindrops and sunlight that would be otherwise lost to reflection.

Benefits of Solar Hybrid Panels  

Until now solar cells have this drawback of producing energy only in the presence of sunlight, making it impossible to harness energy during the rainy season. Countries in the northern hemisphere were not able to switch to solar energy due to the presence of low-intensity sunlight.

With hybrid solar panels, anyone in the world could harness solar power. Researchers expect that in a few years, these panels will be efficient enough to provide electricity for homes and businesses and thus ending our dependency on fossil fuels.

They will also save a lot of money on daily electricity bills. Even though the initial setup costs are higher, countries with good exposure to both sunlight and rain can expect a good ROI.

Hurdles in Solar hybrid panels    

The current designs are not efficient enough to be used commercially. The device was tested in various simulated weather conditions, in sunlight, the device was able to produce around 13% efficiency and simulated raindrops had an efficiency of around 6%.

Currently used commercial solar cells gives an efficiency of around 15%, thus the new design is a viable option for presently used solar panels. However, the efficiency of triboelectric nanogenerators was not reported.

Conclusion

With continuous depletion of non-renewable sources and the disastrous climate change occurring due to fossil fuels, many countries are moving towards eco-friendly alternatives. Solar energy is one of the cleanest energy available. With the advent of new technology like the hybrid solar panels, we can hope to achieve a viable method of electricity generation.

Researchers are continuously trying to improve the efficiency of hybrid solar cells in order to make it commercially available. This will boost our efforts of producing energy in all-weather condition, which is not possible with the currently available technology. With the expansion of solar energy projects worldwide, researchers of hybrid solar cells are expecting to roll out commercial designs in next five years.

Researchers at china are even trying to integrate this new technology into mobile and electronic device such as electronic clothing.     

How a ‘solar battery’ could bring electricity to rural areas – A ‘solar flow’ battery could “Harvest (energy) in the Daytime and Provide Electricity in the Evening

New solar flow battery with a 14.1 percent efficiency. Photo: David Tenenbaum, UW-Madison

Solar energy is becoming more and more popular as prices drop, yet a home powered by the Sun isn’t free from the grid because solar panels don’t store energy for later. Now, researchers have refined a device that can both harvest and store solar energy, and they hope it will one day bring electricity to rural and underdeveloped areas.

The problem of energy storage has led to many creative solutions, like giant batteries. For a paper published today in the journal Chem, scientists trying to improve the solar cells themselves developed an integrated battery that works in three different ways.

It can work like a normal solar cell by converting sunlight to electricity immediately, explains study author Song Jin, a chemist at the University of Wisconsin at Madison. It can store the solar energy, or it can simply be charged like a normal battery.

“IT COULD HARVEST IN THE DAYTIME, PROVIDE ELECTRICITY IN THE EVENING.”

It’s a combination of two existing technologies: solar cells that harvest light, and a so-called flow battery.

The most commonly used batteries, lithium-ion, store energy in solid materials, like various metals. Flow batteries, on the other hand, store energy in external liquid tanks.

What is A ‘Flow Battery’

This means they are very easy to scale for large projects. Scaling up all the components of a lithium-ion battery might throw off the engineering, but for flow batteries, “you just make the tank bigger,” says Timothy Cook, a University at Buffalo chemist and flow battery expert not involved in the study.

“You really simplify how to make the battery grow in capacity,” he adds. “We’re not making flow batteries to power a cell phone, we’re thinking about buildings or industrial sites.

Jin and his team were the first to combine the two features. They have been working on the battery for years, and have now reached 14.1 percent efficiency.

Jin calls this “round-trip efficiency” — as in, the efficiency from taking that energy, storing it, and discharging it. “We can probably get to 20 percent efficiency in the next few years, and I think 25 percent round-trip is not out of the question,” Jin says.

Apart from improving efficiency, Jin and his team want to develop a better design that can use cheaper materials.

The invention is still at proof-of-concept stage, but he thinks it could have a large impact in less-developed areas without power grids and proper infrastructure. “There, you could have a medium-scale device like this operate by itself,” he says. “It could harvest in the daytime, provide electricity in the evening.” In many areas, Jin adds, having electricity is a game changer, because it can help people be more connected or enable more clinics to be open and therefore improve health care.

And Cook notes that if the solar flow battery can be scaled, it can still be helpful in the US.

The United States might have plenty of power infrastructure, but with such a device, “you can disconnect and have personalized energy where you’re storing and using what you need locally,” he says. And that could help us be less dependent on forms of energy that harm the environment.

NREL, University of Washington Scientists Elevate Quantum Dot Solar Cell World Record to 13.4 Percent

Researchers at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) established a new world efficiency record for quantum dot solar cells, at 13.4 percent.

Colloidal quantum dots are electronic materials and because of their astonishingly small size (typically 3-20 nanometers in dimension) they possess fascinating optical properties. 

Quantum dot solar cells emerged in 2010 as the newest technology on an NREL chart that tracks research efforts to convert sunlight to electricity with increasing efficiency. 

The initial lead sulfide quantum dot solar cells had an efficiency of 2.9 percent. Since then, improvements have pushed that number into double digits for lead sulfide reaching a record of 12 percent set last year by the University of Toronto. 

The improvement from the initial efficiency to the previous record came from better understanding of the connectivity between individual quantum dots, better overall device structures and reducing defects in quantum dots.

 NREL scientists Joey Luther and Erin Sanehira are part of a team that has helped NREL set an efficiency record of 13.4% for a quantum dot solar cell.

The latest development in quantum dot solar cells comes from a completely different quantum dot material. The new quantum dot leader is cesium lead triiodide (CsPbI3), and is within the recently emerging family of halide perovskite materials. 

In quantum dot form, CsPbI3 produces an exceptionally large voltage (about 1.2 volts) at open circuit.

“This voltage, coupled with the material’s bandgap, makes them an ideal candidate for the top layer in a multijunction solar cell,” said Joseph Luther, a senior scientist and project leader in the Chemical Materials and Nanoscience team at NREL. 

The top cell must be highly efficient but transparent at longer wavelengths to allow that portion of sunlight to reach lower layers. 
Tandem cells can deliver a higher efficiency than conventional silicon solar panels that dominate today’s solar market.

This latest advance, titled “Enhanced mobility CsPbI3 quantum dot arrays for record-efficiency, high-voltage photovoltaic cells,” is published in Science Advances. The paper was co-authored by Erin Sanehira, Ashley Marshall, Jeffrey Christians, Steven Harvey, Peter Ciesielski, Lance Wheeler, Philip Schulz, and Matthew Beard, all from NREL; and Lih Lin from the University of Washington.

The multijunction approach is often used for space applications where high efficiency is more critical than the cost to make a solar module. 
The quantum dot perovskite materials developed by Luther and the NREL/University of Washington team could be paired with cheap thin-film perovskite materials to achieve similar high efficiency as demonstrated for space solar cells, but built at even lower costs than silicon technology–making them an ideal technology for both terrestrial and space applications.

“Often, the materials used in space and rooftop applications are totally different. It is exciting to see possible configurations that could be used for both situations,” said Erin Sanehira a doctoral student at the University of Washington who conducted research at NREL.

The NREL research was funded by DOE’s Office of Science, while Sanehira and Lin acknowledge a NASA space technology fellowship.

NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.