Technology developed at the Technion: the oxygen and hydrogen are produced and stored in completely separate cells.
Prof. Avner Rothschild from the Faculty of Materials Science and Engineering
Technology developed at the Technion: the oxygen and hydrogen are produced and stored in completely separate cells.
Prof. Avner Rothschild from the Faculty of Materials Science and Engineering
1. Lots of storage
Batteries will be incentivized or mandated for practically every new solar PV system across the U.S. by 2025. As more homeowners and businesses deploy PV systems to reduce their electricity bills and ensure backup power, simple net metering will increasingly be replaced by time-of-use rates and other billing mechanisms that aim to align power prices with utility costs. We already see these trends in California and several states in the Northeast.
Solar systems with batteries are going to be about twice as expensive as traditional grid-direct installations, so in that sense, we will see actual costs increase as the mix shifts toward batteries. But while system costs will go up, we need to be careful to parse the actual equipment and soft costs from the consumer’s cost net of tax credits and incentives. Equipment costs for batteries and other hardware are generally flat to slightly down.
3. More battery and inverter packages from the same brand
Since the battery represents the dominant cost in an energy storage system (ESS), inverter companies will increasingly offer branded batteries. In turn, inverter companies packaging third-party batteries will eventually make way for savvy battery companies that can package the whole system.
4. Energy storage systems treated like heat pumps and air conditioners
California’s new Title 21 requirements make solar PV systems standard issue, and we can expect a future update to do the same for energy storage. By then, builders will be able to choose the ESS line they want to work with, and the whole process will look almost exactly like it does for home mechanical appliances like water heaters and HVAC systems. The only question will be whether the ESS is packaged with solar panels or kept separate.
5. Reputation will matter — a lot
The lack of meaningful industry metrics in energy storage creates an environment where branding and reputation become important, since users have little information beyond messaging and word of mouth. Long-term, this will create a barrier to entry for new battery startups, so expect fewer total players once a handful of brands emerge as high-confidence choices.
6. New safety standards and code requirements catch up to technology
Last October, the National Fire Protection Association published the first edition of the NFPA 855 code, which establishes an industrywide safety standard for energy storage systems. Test standards, including UL 9540, and UL 9540A, as well as building and electrical codes, such as the National Electrical Code (NEC/NFPA 70), International Residential Code and International Fire Code, are already being updated to harmonize with NFPA 855. The upshot is that kilowatt-hour capacity limits, siting and protective equipment requirements are becoming standardized and more accessible for both installers and inspectors to understand and apply.
7. Real automation and optimization software will outpace flashy interfaces
Third-party owners have specific PV fleet-management needs and often have proprietary software that their ESS needs to interface with daily. IEEE 2030.5 and related standards will help facilitate this need. Local installers have little in the way of hard requirements, but they and their customers will expect systems to be easy to install and operate.
In the long term, we’ll see real automation and optimization rather than the data-palooza common today. Many interfaces report too much data, and simplifying systems to hide irrelevant data will be necessary to avoid alienating the more mainstream consumers.
8. Still waiting for vehicle-to-grid
While V2G is not primarily a technical challenge, some manufacturers like Nissan and Honda have made significant headway. The challenge is more procedural than technical. V2G applications will take off when vehicle manufacturers and interface providers come to terms with how and when an electric vehicle’s battery is used for grid services or backup and how that impacts the EV’s warranty.
There’s also a consumer confidence problem to overcome, especially for those relying solely on their EV for transportation. We’re more likely to see “second-life” EV batteries repackaged for stationary storage — which is much easier to manage than trying to use the battery in the car.
9. AC and DC coupling will both be around for the foreseeable future
Given the latest National Electrical Code requirements for rapid shutdown, as well as the fact that module-level systems (e.g., Enphase and SolarEdge) represent the majority of installed systems, AC coupling is the clear choice for existing system owners to add batteries.
AC coupling will enjoy at least a temporary boom in popularity as people with existing PV systems seek to add storage. However, most advantages of AC coupling are for retrofits, and the majority of new systems will enjoy lower costs and better performance via DC coupling. DC coupling is arguably going to become more dominant once the PV-only retrofit market is saturated.
10. Battery pack voltage will increase dramatically
A century of lead-acid battery dominance has entrenched 48 volts (DC) as the standard battery system voltage. Systems with voltages up to 1,000 VDC are deployed using standard lead-acid cells, but it is only practical for engineered commercial and industrial or utility systems.
The Ohm’s law tradeoff between current and voltage pushed the EV industry, which needs to reduce weight and cost everywhere it can, to quickly migrate to high-voltage battery packs using 3- to 4-VDC lithium-ion cells. Similarly, the stationary energy storage industry is adopting higher-voltage battery packs to reduce the cost of battery inverters. Since conductor losses increase and decrease exponentially with current, higher battery voltages also enable better system efficiency.
The decade of the 2020s will ring in the age of mass solar-plus-storage solution deployment, allowing businesses and residents to tap into renewables more efficiently, protect against outages, save money and live more sustainably.
*** Re-Posted from Green-Tech Media
Can we use mountains as gigantic batteries for long-term energy storage? Such is the premise of new research published in the journal Energy.
The particular focus of the study by Julian Hunt of IIASA (Austria-based International Institute for Applied Systems Analysis) and his colleagues is how to store energy in locations that have less energy demand and variable weather conditions that affect renewable energy sources.
The team looked at places like small islands and remote places that would need less than 20 megawatts of capacity for energy storage and proposed a way to use mountains to accomplish the task.
Hunt and his team want to use a system dubbed Mountain Gravity Energy Storage (or MGES). MGES employes cranes positioned on the edge of a steep mountain to move sand (or gravel) from a storage site at the bottom to a storage site at the top.
Like in a ski-lift, a motor/generator would transport the storage vessels, storing potential energy. Electricity is generated when the sand is lowered back from the upper site.
How much energy is created? The system takes advantage of gravity, with the energy output being proportional to the sand’s mass, gravity and the height of the mountain. Some energy would be lost due in the loading and unloading process.
Hydropower can also be employed from any kind of mountainous water source, like river streams. When it’s available, water would be used to fill storage containers instead of sand or gravel, generating electricity in that fashion.
Utilizing the mountain, hydropower can be invoked from any height of the system, making it more flexible than usual hydropower, explains the press release from IIASA.
There are specific advantages to using sand, however, as Hunt explained:
“One of the benefits of this system is that sand is cheap and, unlike water, it does not evaporate – so you never lose potential energy and it can be reused innumerable times,” said Hunt. “This makes it particularly interesting for dry regions.”
Where would be the ideal places to install such a system? The researchers are thinking of locations with high mountains, like the Himalayas, Alps, and Rocky Mountains or islands like Hawaii, Cape Verde, Madeira, and the Pacific Islands that have mountainous terrains.
The scientists use the Molokai Island in Hawaii as an example in their paper, outlining how all of the island’s energy needs can be met with wind, solar, batteries and their MGES setup.
The MGES system.
“It is important to note that the MGES technology does not replace any current energy storage options but rather opens up new ways of storing energy and harnessing untapped hydropower potential in regions with high mountains,” Hunt noted.
Invisible infrared light accounts for half of all solar radiation on the Earth’s surface, yet ordinary solar energy systems have limited ability in converting it to power. A breakthrough in research at KTH could change that.
A research team led by Hans Ågren, professor in theoretical chemistry at KTH Royal Institute of Technology, has developed a film that can be applied on top of ordinary solar cells, which would enable them to use infrared light in energy conversion and increase efficiency by 10 percent or more.
“We have achieved a 10 percent increase in efficiency without yet optimizing the technology,” Ågren says. “With a little more work, we estimate that a 20 to 25 percent increase in efficiency could be achieved.”
Photosensitive materials used in solar cells, such as the mineral perovskite, have a limited ability to respond to infrared light. The solution, developed with KTH researchers Haichun Liu and Qingyun Liu, was to combine nanocrystals with chains of microlenses.
“The ability of the microlenses to concentrate light allows the nanoparticles to convert the weak IR light radiation to visible light useful for solar cells,” Ågren says.
The research progress has been patented, and presented in the scientific journal Nanoscale.
More information: Qingyun Liu et al. Microlens array enhanced upconversion luminescence at low excitation irradiance, Nanoscale (2019). DOI: 10.1039/c9nr03105g
Journal information: Nanoscale
Provided by KTH Royal Institute of Technology
Researchers at the University of Waterloo have developed a way to better harness the volume of energy collected by solar panels.
In a new study, the researchers developed an algorithm that increases the efficiency of the solar photovoltaic (PV) system and reduces the volume of power currently being wasted due to a lack of effective controls.
“We’ve developed an algorithm to further boost the power extracted from an existing solar panel,” said Milad Farsi, a PhD candidate in Waterloo’s Department of Applied Mathematics. “Hardware in every solar panel has some nominal efficiency, but there should be some appropriate controller that can get maximum power out of solar panels.
“We do not change the hardware or require additional circuits in the solar PV system. What we developed is a better approach to controlling the hardware that already exists.”
The new algorithm enables controllers to better deal with fluctuations around the maximum power point of a solar PV system, which have historically led to the wasting of potential energy collected by panels.
“Based on the simulations, for a small home-use solar array including 12 modules of 335W, up to 138.9 kWh/year can be saved,” said Farsi, who undertook the study with his supervisor, Professor Jun Liu of Waterloo’s Department of Applied Mathematics. “The savings may not seem significant for a small home-use solar system but could make a substantial difference in larger-scale ones, such as a solar farm or in an area including hundreds of thousands of local solar panels connected to the power grid.
“Taking Canada’s largest PV plant, for example, the Sarnia Photovoltaic Power Plant, if this technique is used, the savings could amount to 960,000 kWh/year, which is enough to power hundreds of households. If the saved energy were to be generated by a coal-fired plant, it would require emission of 312 tonnes of CO2 into the atmosphere.”
Milad further pointed out that the savings could be even more substantial under a fast-changing ambient environment, such as Canadian weather conditions, or when the power loss in the converters due to the undesired chattering effects seen in other conventional control methods is taken into account.
The study, Nonlinear Optimal Feedback Control and Stability Analysis of Solar Photovoltaic Systems, authored by Waterloo’s Faculty of Mathematics researchers Farsi and Liu, was recently published in the journal IEEE Transactions on Control Systems Technology.
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.
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.
Researchers at Swinburne, the University of Sydney and Australian National University have collaborated to develop a solar absorbing, ultra-thin graphene-based film with unique properties that has great potential for use in solar thermal energy harvesting.
The 90 nanometre material is said to be a 1000 times finer than a human hair and is able to rapidly heat up to 160°C under natural sunlight in an open environment.
The team stated that this new graphene-based material may also open new avenues in:
The researchers have developed a 2.5cm x 5cm working prototype to demonstrate the photo-thermal performance of the graphene-based metamaterial absorber. They have also proposed a scalable manufacturing strategy to fabricate the proposed graphene-based absorber at low cost.
“This is among many graphene innovations in our group,” says Professor Baohua Jia, Research Leader, Nanophotonic Solar Technology, in Swinburne’s Center for Micro-Photonics.
“In this work, the reduced graphene oxide layer and grating structures were coated with a solution and fabricated by a laser nanofabrication method, respectively, which are both scalable and low cost.”
“Our cost-effective and scalable graphene absorber is promising for integrated, large-scale applications that require polarisation-independent, angle insensitive and broad bandwidth absorption, such as energy-harvesting, thermal emitters, optical interconnects, photodetectors and optical modulators,” says first author of this research paper, Dr Han Lin, Senior Research Fellow in Swinburne’s Center for Micro-Photonics.
“Fabrication on a flexible substrate and the robustness stemming from graphene make it suitable for industrial use,” Dr Keng-Te Lin, another author, added.
“The physical effect causing this outstanding absorption in such a thin layer is quite general and thereby opens up a lot of exciting applications,” says Dr Bjorn Sturmberg, who completed his PhD in physics at the University of Sydney in 2016 and now holds a position at the Australian National University.
“The result shows what can be achieved through collaboration between different universities, in this case with the University of Sydney and Swinburne, each bringing in their own expertise to discover new science and applications for our science,” says Professor Martijn de Sterke, Director of the Institute of Photonics and Optical Science.
“Through our collaboration we came up with a very innovative and successful result. We have essentially developed a new class of optical material, the properties of which can be tuned for multiple uses.”
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.
As the solar industry has grown, so have some of its inefficiencies. Smart entrepreneurs see those inefficiencies as business opportunities and try to create solutions around them. Such is the nature of a maturing industry.
One of the biggest complications emerging from the industry’s breakneck growth is the maintenance of solar farms. Historically, technicians have run electrical tests on random sections of solar cells in order to identify problems. In recent years, the use of drones equipped with thermal cameras has improved the speed of data collection, but now technicians are being asked to interpret a never-ending flow of unstructured data.
That’s where Raptor Maps comes in. The company’s software analyzes imagery from drones and diagnoses problems down to the level of individual cells. The system can also estimate the costs associated with each problem it finds, allowing technicians to prioritize their work and owners to decide what’s worth fixing.
“We can enable technicians to cover 10 times the territory and pinpoint the most optimal use of their skill set on any given day,” Raptor Maps co-founder and CEO Nikhil Vadhavkar says. “We came in and said, ‘If solar is going to become the number one source of energy in the world, this process needs to be standardized and scalable.’ That’s what it takes, and our customers appreciate that approach.”
Raptor Maps processed the data of 1 percent of the world’s solar energy in 2018, amounting to the energy generated by millions of panels around the world. And as the industry continues its upward trajectory, with solar farms expanding in size and complexity, the company’s business proposition only becomes more attractive to the people driving that growth.
Picking a path
Raptor Maps was founded by Eddie Obropta ’13 SM ’15, Forrest Meyen SM ’13 PhD ’17, and Vadhavkar, who was a PhD candidate at MIT between 2011 and 2016. The former classmates had worked together in the Human Systems Laboratory of the Department of Aeronautics and Astronautics when Vadhavkar came to them with the idea of starting a drone company in 2015.
The founders were initially focused on the agriculture industry. The plan was to build drones equipped with high-definition thermal cameras to gather data, then create a machine-learning system to gain insights on crops as they grew. While the founders began the arduous process of collecting training data, they received guidance from MIT’s Venture Mentoring Service and the Martin Trust Center. In the spring of 2015, Raptor Maps won the MIT $100K Launch competition.
But even as the company began working with the owners of two large farms, Obropta and Vadhavkar were unsure of their path to scaling the company. (Meyen left the company in 2016.) Then, in 2017, they made their software publicly available and something interesting happened.
They found that most of the people who used the system were applying it to thermal images of solar farms instead of real farms. It was a message the founders took to heart.
“Solar is similar to farming: It’s out in the open, 2-D, and it’s spread over a large area,” Obropta says. “And when you see [an anomaly] in thermal images on solar, it usually means an electrical issue or a mechanical issue — you don’t have to guess as much as in agriculture. So we decided the best use case was solar. And with a big push for clean energy and renewables, that aligned really well with what we wanted to do as a team.”
Obropta and Vadhavkar also found themselves on the right side of several long-term trends as a result of the pivot. The International Energy Agency has proposed that solar power could be the world’s largest source of electricity by 2050. But as demand grows, investors, owners, and operators of solar farms are dealing with an increasingly acute shortage of technicians to keep the panels running near peak efficiency.
Since deciding to focus on solar exclusively around the beginning of 2018, Raptor Maps has found success in the industry by releasing its standards for data collection and letting customers — or the many drone operators the company partners with — use off-the-shelf hardware to gather the data themselves. After the data is submitted to the company, the system creates a detailed map of each solar farm and pinpoints any problems it finds.
“We run analytics so we can tell you, ‘This is how many solar panels have this type of issue; this is how much the power is being affected,’” Vadhavkar says. “And we can put an estimate on how many dollars each issue costs.”
The model allows Raptor Maps to stay lean while its software does the heavy lifting. In fact, the company’s current operations involve more servers than people.
The tiny operation belies a company that’s carved out a formidable space for itself in the solar industry. Last year, Raptor Maps processed four gigawatts worth of data from customers on six different continents. That’s enough energy to power nearly 3 million homes.
Vadhavkar says the company’s goal is to grow at least fivefold in 2019 as several large customers move to make the software a core part of their operations. The team is also working on getting its software to generate insights in real time using graphical processing units on the drone itself as part of a project with the multinational energy company Enel Green Power.
Ultimately, the data Raptor Maps collect are taking the uncertainty out of the solar industry, making it a more attractive space for investors, operators, and everyone in between.
“The growth of the industry is what drives us,” Vadhavkar says. “We’re directly seeing that what we’re doing is impacting the ability of the industry to grow faster. That’s huge. Growing the industry — but also, from the entrepreneurial side, building a profitable business while doing it — that’s always been a huge dream.”
Solar rays are a plentiful, clean source of energy that is becoming increasingly important as the world works to shift away from power sources that contribute to global warming.
But current methods of harvesting solar charges are in large expensive and inefficient—with a theoretical efficiency limit of 33 percent. New nanomaterials developed by researchers at the Advanced Science Research Center (ASRC) at The Graduate Center of The City University of New York (CUNY) could provide a pathway to more efficient and potentially affordable harvesting of solar energy.
The materials, created by scientists with the ASRC’s Nanoscience Initiative, use a process called singlet fission to produce and extend the life of harvestable light-generated electrons. The discovery is described in a newly published paper in the Journal of Physical Chemistry. Early research suggests these materials could create more usable charges and increase the theoretical efficiency of solar cells up to 44 percent.
“We modified some of the molecules in commonly used industrial dyes to create self-assembling materials that facilitate a greater yield of harvestable electrons and extend the electrons’ xcited-state lifetimes, giving us more time to collect them in a solar cell,” said Andrew Levine, lead author of the paper and a Ph.D. student at The Graduate Center.
The self-assembly process, Levine explained, causes the dye molecules to stack in a particular way. This stacking allows dyes that have absorbed solar photons to couple and share energy with —or “excite”—neighboring dyes. The electrons in these dyes then decouple so that they can be collected as harvestable solar energy.
Methodology and Findings
To develop the materials, researchers combined various versions of two frequently used industrial dyes—diketopyrrolopyrrole (DPP) and rylene. This resulted in the formation of six self-assembling superstructures, which scientists investigated using electron microscopy and advanced spectroscopy. They found that each combination had subtle differences in geometry that affected the dyes’ excited states, the occurrence of singlet fission, and the yield and lifetime of harvestable electrons. Significance
“This work provides us with a library of nanomaterials that we can study for harvesting solar energy,” said Professor Adam Braunschweig, lead researcher on the study and an associate professor with the ASRC Nanoscience Initiative and the Chemistry Departments at Hunter College and The Graduate Center. “Our method for combining the dyes into functional materials using self-assembly means we can carefully tune their properties and increase the efficiency of the critical light-harvesting process.”
The materials’ ability to self-assemble could also shorten the time for creating commercially viable solar cells, said the researchers, and prove more affordable than current fabrication methods, which rely on the time-consuming process of molecular synthesis.
The research team’s next challenge is to develop a method of harvesting the solar charges created by their new nanomaterials. Currently, they are working to design a rylene molecule that can accept the electron from the DPP molecule after the singlet fission process. If successful, these materials would both initiate the singlet fission process and facilitate charge-transfer into a solar cell.
Explore further: Pathway opens to minimize waste in solar energy capture
More information: Andrew M. Levine et al, Singlet Fission in Combinatorial Diketopyrrolopyrrole–Rylene Supramolecular Films, The Journal of Physical Chemistry C (2019). DOI: 10.1021/acs.jpcc.8b09593