NREL: Semiconducting Single-Walled Carbon Nanotubes in Solar Energy Harvesting


National Renewable Energy Laboratory, Golden, Colorado 

Semiconducting single-walled carbon nanotubes (s-SWCNTs) represent a tunable model one-dimensional system with exceptional optical and electronic properties. 

High-throughput separation and purification strategies have enabled the integration of s-SWCNTs into a number of optoelectronic applications, including photovoltaics (PVs). In this Perspective, we discuss the fundamental underpinnings of two model PV interfaces involving s-SWCNTs. 

We first discuss s-SWCNT–fullerene heterojunctions where exciton dissociation at the donor–acceptor interface drives solar energy conversion. Next, we discuss charge extraction at the interface between s-SWCNTs and a photoexcited perovskite active layer. 

In each case, the use of highly enriched semiconducting SWCNT samples enables fundamental insights into the thermodynamic and kinetic mechanisms that drive the efficient conversion of solar photons into long-lived separated charges. 

These model systems help to establish design rules for next-generation PV devices containing well-defined organic semiconductor layers and help to frame a number of important outstanding questions that can guide future studies.

EPPL Creates a low-cost system for splitting carbon dioxide – Turning Renewable Energy into Fuel


Ball-and-stick model of carbon dioxide. Credit: Wikipedia

Using Earth-abundant materials, EPFL scientists have built the first low-cost system for splitting CO2 into CO, a reaction necessary for turning renewable energy into fuel.
The future of clean energy depends on our ability to efficiently store energy from renewable sources and use it later. 


A popular way to do this is to electrolyze carbon dioxide to carbon monoxide, which is then mixed with hydrogen to produce liquid hydrocarbons like gasoline or kerosene that can be used as fuel. 

However, we currently lack efficient and Earth-abundant catalysts for the initial splitting of CO2 into CO and oxygen, which makes the move into renewable energy expensive and prohibitive. 

EPFL scientists have now developed an Earth-abundant catalyst based on copper-oxide nanowires modified with tin oxide. 
The system can split CO2 with an efficiency of 13.4%. 
The work is published in Nature Energy, and can help worldwide efforts to synthetically produce carbon-based fuels from CO2 and water.

The research was carried out by the lab of Michael Grätzel at EPFL. Grätzel is known worldwide for the invention of the first ever dye-sensitized solar cells (or “Grätzel cells”). 

The catalyst, developed by PhD student Marcel Schreier and postdoc Jingshan Luo, is made by depositing an atomic layer of tin oxide on copper oxide nanowires

By using such Earth-abundant materials, the design keeps the cost of the catalyst low while significantly increasing the yield of CO, as opposed to the other products that are generated from CO2 electrocatalysis.
The catalyst was integrated into a CO2 electrolysis system and linked to a triple-junction solar cell (GaInP/GaInAs/Ge) to make a CO2 electrolyzer. 

The system uses the catalyst as a bifunctional electrode that both reduces CO2 into CO and produces oxygen through what is known as the “oxygen evolution” reaction. The two products are separated with a bipolar membrane.

Using solar energy, the system was able to selectively convert CO2 to CO with an efficiency of 13.4%, and do so with a Faradaic efficiency up to 90%—this describes how efficiently electrical charge is transferred in a electrocatalysis system like the one developed here. “The work sets a new benchmark for solar-driven CO2 reduction,” says Luo.

“This is the first time that such a bi-functional and low-cost catalyst is demonstrated,” adds Schreier. “Very few catalysts—except expensive ones, like gold and silver—can selectively transform CO2 to CO in water, which is crucial for industrial applications.”

 
More information: Marcel Schreier, Florent Héroguel, Ludmilla Steier, Shahzada Ahmad, Jeremy S. Luterbacher, Matthew T. Mayer, Jingshan Luo, Michael Grätzel. Solar conversion of CO2 to CO using Earth-abundant electrocatalysts prepared by atomic layer modification of CuO. Nature Energy 2, 17087 (05 June 2017). nature.com/articles/doi:10.1038/nenergy.2017.87
Provided by: Ecole Polytechnique Federale de Lausanne

Energy from the sun, stored in a liquid – and released on demand OR … Solar to Hydrogen Fuel … And the Winner Is?


Liquid Solar Sweeden large_RkeCoGI3VB0jjnprwamEX8rEU6kapTZ8SQd-0sN5fzs

“The solar energy business has been trying to overcome … challenge for years. The cost of installing solar panels has fallen dramatically but storing the energy produced for later use has been problematic.”

Solar Crash I solar-and-wind-energy“In a single hour, the amount of power from the sun that strikes the Earth is more than the entire world consumes in an year.” To put that in numbers, from the US Department of Energy 

 

 

Each hour 430 quintillion Joules of energy from the sun hits the Earth. That’s 430 with 18 zeroes after it! In comparison, the total amount of energy that all humans use in a year is 410 quintillion JoulesFor context, the average American home used 39 billion Joules of electricity in 2013.

HOME SOLAR-master675Read About: What are the Most Efficient Solar Panels on the Market?

 

Clearly, we have in our sun “a source of unlimited renewable energy”. But how can we best harness this resource? How can we convert and  “store” this energy resource on for sun-less days or at night time … when we also have energy needs?

Now therein lies the challenge!

Would you buy a smartphone that only worked when the sun was shining? Probably not. What it if was only half the cost of your current model: surely an upgrade would be tempting? No, thought not.

The solar energy business has been trying to overcome a similar challenge for years. The cost of installing solar panels has fallen dramatically but storing the energy produced for later use has been problematic.

 

Now scientists in Sweden have found a new way to store solar energy in chemical liquids. Although still in an early phase, with niche applications, the discovery has the potential to make solar power more practical and widespread.

Until now, solar energy storage has relied on batteries, which have improved in recent years. However, they are still bulky and expensive, and they degrade over time.

Image: Energy and Environmental Science

Trap and release solar power on demand

A research team from Chalmers University of Technology in Gothenburg made a prototype hybrid device with two parts. It’s made from silica and quartz with tiny fluid channels cut into both sections.

 

The top part is filled with a liquid that stores solar energy in the chemical bonds of a molecule. This method of storing solar energy remains stable for several months. The energy can be released as heat whenever it is required.

The lower section of the device uses sunlight to heat water which can be used immediately. This combination of storage and water heating means that over 80% of incoming sunlight is converted into usable energy.

Suddenly, solar power looks a lot more practical. Compared to traditional battery storage, the new system is more compact and should prove relatively inexpensive, according to the researchers. The technology is in the early stages of development and may not be ready for domestic and business use for some time.

 

From the lab to off-grid power stations or satellites?

The researchers wrote in the journal Energy & Environmental Science: “This energy can be transported, and delivered in very precise amounts with high reliability(…) As is the case with any new technology, initial applications will be in niches where [molecular storage] offers unique technical properties and where cost-per-joule is of lesser importance.”

A view of solar panels, set up on what will be the biggest integrated solar panel roof of the world, in a farm in Weinbourg, Eastern France February 12, 2009. Bright winter sun dissolves a blanket of snow on barn roofs to reveal a bold new sideline for farmer Jean-Luc Westphal: besides producing eggs and grains, he is to generate solar power for thousands of homes. Picture taken February 12.         To match feature FRANCE-FARMER/SOLAR              REUTERS/Vincent Kessler  (FRANCE) - RTXC0A6     Image: REUTERS: Kessler

The team now plans to test the real-world performance of the technology and estimate how much it will cost. Initially, the device could be used in off-grid power stations, extreme environments, and satellite thermal control systems.

 

Editor’s Note: As Solomon wrote in  Ecclesiastes 1:9:What has been will be again, what has been done will be done again; there is nothing new under the sun.”

Storing Solar Energy chemically and converting ‘waste heat’ has and is the subject of many research and implementation Projects around the globe. Will this method prove to be “the one?” This writer (IMHO) sees limited application, but not a broadly accepted and integrated solution.

Solar Energy to Hydrogen Fuel

So where does that leave us? We have been following the efforts of a number of Researchers/ Universities who are exploring and developing “Sunlight to Hydrogen Fuel” technologies to harness the enormous and almost inexhaustible energy source power-house … our sun! What do you think? Please leave us your Comments and we will share the results with our readers!

Read More

We have written and posted extensively about ‘Solar to Hydrogen Renewable Energy’ – here are some of our previous Posts:

Sunlight to hydrogen fuel 10-scientistsusScientists using sunlight, water to produce renewable hydrogen power

 

 

Rice logo_rice3Solar-Powered Hydrogen Fuel Cells

Researchers at Rice University are on to a relatively simple, low-cost way to pry hydrogen loose from water, using the sun as an energy source. The new system involves channeling high-energy “hot” electrons into a useful purpose before they get a chance to cool down. If the research progresses, that’s great news for the hydrogen […]

HyperSolar 16002743_1389245094451149_1664722947660779785_nHyperSolar reaches new milestone in commercial hydrogen fuel production

HyperSolar has achieved a major milestone with its hybrid technology HyperSolar, a company that specializes in combining hydrogen fuel cells with solar energy, has reached a significant milestone in terms of hydrogen production. The company harnesses the power of the sun in order to generate the electrical power needed to produce hydrogen fuel. This is […]

riceresearch-solar-water-split-090415 (1)Rice University Research Team Demonstrates Solar Water-Splitting Technology: Renewable Solar Energy + Clean – Low Cost Hydrogen Fuel

Rice University researchers have demonstrated an efficient new way to capture the energy from sunlight and convert it into clean, renewable energy by splitting water molecules. The technology, which is described online in the American Chemical Society journal Nano Letters, relies on a configuration of light-activated gold nanoparticles that harvest sunlight and transfer solar energy […]

NREL I downloadNREL Establishes World Record for Solar Hydrogen Production

NREL researchers Myles Steiner (left), John Turner, Todd Deutsch and James Young stand in front of an atmospheric pressure MDCVD reactor used to grow crystalline semiconductor structures. They are co-authors of the paper “Direct Solar-to-Hydrogen Conversion via Inverted Metamorphic Multijunction Semiconductor Architectures” published in Nature Energy. Photo by Dennis Schroeder.   Scientists at the U.S. […]

NREL CSM Solar Hydro img_0095NREL & Colorado School of Mines Researchers Capture Excess Photon Energy to Produce Solar Fuels

Photo shows a lead sulfide quantum dot solar cell. A lead sulfide quantum dot solar cell developed by researchers at NREL. Photo by Dennis Schroeder.

Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have developed a proof-of-principle photo-electro-chemical cell capable of capturing excess photon energy normally lost to generating heat. Using quantum […]

What is up with the U.S. ‘Solar Industry’? Is There and Impending US Solar Energy Crash?


Solar Crash I solar-and-wind-energy

After nice stretch of sunny weather, the last few months have clouded over for big solar. Declining prices for photovoltaic cells are hurting panel manufacturers and stressing solar installation businesses.

This situation was in sharp relief this week in Tesla’s (TSLA Tesla Motors Inc TSLA 307.19 -0.38%) earnings, as its solar installation business, SolarCity, disclosed a big slowdown in builds. SolarCity commands 41 percent of the residential solar installation market, according to GTM. In its latest earnings, the firm revealed that it had installed 150 MW of panels in the first quarter, down nearly 39 percent y/y.

“Rather than prioritizing the growth of MW of solar deployed at any cost, we are selectively deploying projects that have higher margin and generate cash up front. Consequently, solar energy generation deployments in Q1 2017 declined year-over-year, but had better financial results,” said the earnings release.

The Curious Logic of the Solar Market

Industry body Solar Energy Industries Association (SEIA) reports that installations for the past year actually went up. In 2016, the U.S. saw 14.8GW solar capacity installed with a new installation taking place every 84 seconds.

There are companies that are doing well. First Solar (FSLR First Solar In FSLR 35.15 +1.77%) just reported strong earnings while Vivint Solar (VSLR Vivint Solar Inc VSLR 3.00+1.70%) announced is expansion into Rhode Island and is expected to announce financial results next week. However, the list of struggling companies in the sector is longer.

SunPower Corp. (SPWR) reported its sixth consecutive quarter of losses and laid off 25 percent of its workforce. Verengo Solar filed for bankruptcy last year, while Sungevity and Suninva did the same earlier this year.

But if solar energy is seeing such high demand, why are the companies feeling the heat?

The Price Is Not Right

The cost of the production and installation of solar panels has dropped dramatically and that is driving demand. According to SEIA, the cost to install solar capacity dropped 29 percent in the final quarter of 2016, compared to the same period last year. Over the past 10 years, installation costs have come down by nearly 60 percent.

There is more than one reason for price suppression in the solar industry.

“Driving the cost reductions were lower module and inverter prices, increased competition, lower installer and developer overheads, improved labor productivity, and optimized system configurations,” a National Renewable Energy Laboratory report states.

At home, the government tried to promote solar energy to consumers by making it affordable. One such initiative was the Solar Investment Tax Credit for residential and business solar installations, adopted in 2006 and extended in 2015.

In the international arena, U.S. solar companies blame declining panel prices on foreign imports, especially from countries like China, Mexico and Canada. Suniva recently implored President Trump for protectionist policies for the sector.

However, as the big ones struggled, someone made hay as the sun shone. According to GTM research’s U.S. Residential Solar Update 2017, many of the larger firms struggled to do well while smaller, local companies thrived.

More Insights: Investopedia http://www.investopedia.com/news/solar-industry-slowdown-catches-solarcity/#ixzz4gWsv7IYa

Perovskite Nanocrystals: Bright – Cheap – Stable: Discovery Illuminates Path to Highly Efficient Perovskite based Quantum Dots Photovoltaics


Perovskite Nanocrystals id46560

Digital picture of colloidal solution in toluene taken under UV-light (λ = 365 nm) and crystal structure of Formamidinium lead-halide perovskite. (Image: Friedrich-Alexander-Universität Erlangen-Nürnberg)

The team reports facile and rapid room temperature synthesis of cubic and platelet-like colloidal nanocrystals (NCs) of Formamidinium Lead Halide Perovskite FAPbX3 (X=Cl, Br, I, or mixed Cl/Br and Br/I) by ligand-assisted re-precipitation method (LARP).
The obtained NCs are 15-25 nm in size and exhibit a remarkably high photoluminescence quantum yield of up to 85% as well as colloidal and chemical stability.
The cubic and platelet-like NCs with their emission in the range of 415-740 nm, full width at half maximum of 20-44 nm and radiative lifetimes of 5-166 ns, allow precise band gap tuning by halide composition as well as by tailoring their dimensions.
Notably, for the first time they have demonstrate thermodynamically stable FAPbI3 NCs in the black cubic α-phase without transition to the yellow hexagonal δ-phase even after 150 days of storage. This is in strong contrast to polycrystalline films and single crystals which convert within hours.
This fact paves the way to highly efficient perovskite based quantum dots photovoltaics, which is underpinned by demonstrating FAPbI3 NCs based photodetector.
To highlight the potential of FAPbX3 NCs as a promising candidate for optoelectronic and luminescent applications, the scientists modified the surface with polyhedral oligomeric silsesquioxane. This modification protects the brightly luminescent FAPbX3 NCs from decomposition even after storage in water for more than 2 months.
Source: Friedrich-Alexander-Universität Erlangen-Nürnberg

 

Improving Perovskites to Surpass Silicon Solar Cell Performance: Answers from ANSER


Perovskites Water id46564The perovskite device is made of different layers, each of which has a specific function. Together, the titanium dioxide and PC61BM layers protect the perovskite from heat and water. (Image: Rebecca Palmer, ANSER EFRC)

 

Harvesting sunlight and using it to power our homes and devices is a reality today. Generally, most commercial solar cells are made of silicon. However, as highlighted previously, a type of material called perovskite halides are a potential competitor of silicon. Unfortunately, most perovskite halides are sensitive to moisture and high temperatures such that exposure to either will quickly degrade these materials — rendering them useless. Researchers at the Argonne-Northwestern Solar Energy Research Center (ANSER) have developed a way to protect perovskites from water and stabilize them against heat. By carefully growing an ultrathin layer of metal oxide on a carbon coating, the researchers made a perovskite device that worked even after dousing the device with a stream of water (Nano Letters, “Liquid Water- and Heat-Resistant Hybrid Perovskite Photovoltaics via an Inverted ALD Oxide Electron Extraction Layer Design”).

Solar cells are made up of layers, each with a specific duty. The perovskite layer absorbs sunlight, which can excite an electron. The electron could go right back to where it started, unless it can be extracted out of the absorbing layer quickly. For this device, the researchers placed a layer of PC61BM, a carbon-based material, on top of the perovskite, which has two roles. First, PC61BM is good at extracting electrons once they are excited by sunlight. Second, the PC61BM layer protects the perovskite from water vapor, which is one of the reactants used for forming the final protective coating — titanium dioxide.
The titanium dioxide layer was grown using atomic layer deposition (ALD), a method that deposits alternating layers of titanium and oxygen atoms. The researchers demonstrated that depositing the titanium dioxide by ALD creates a barrier with no pinholes, effectively blocking moisture from entering the film. Only about 20 nanometers of titanium dioxide on the PC61BM were needed to protect the perovskite. This layer is around 1,000 times thinner than the thickness of a human hair.
On top of the titanium dioxide, aluminum electrodes were deposited and protected by a thin layer of gold. On the opposite side of the perovskite, the team placed a nickel oxide layer that is good at extracting the positively charged holes left by the electrons. Glass, coated with a conductive film, is used as a support that allows light to pass through and a circuit to be formed.
The device held up to pure water and a temperature of 100 °C (around 200 °F) thanks to the titanium dioxide layer. In Soo Kim, a postdoctoral fellow and lead researcher, explained that he was excited about this result. “The key challenge to commercialization of any halide perovskite-based devices is the environmental stability.”
Many people have been studying perovskite halides, but the stability under real-world environmental situations has been largely overlooked. Kim’s work is one of the first examples of protecting perovskite from liquid water with an ultrathin metal oxide layer. Alex Martinson, who directed the work, said, “It is surprising when something simple works so well.”
Martinson explained that perovskite solar cells have a lot of promise because they have the potential to be cheaper than the current commercial devices, such as silicon. The silicon manufacturing process is energy intensive, and silicon materials are required to be highly pure. In contrast, there are many pathways to make perovskites, and the performance of perovskite devices are less sensitive to impurities. Scientists at ANSER are excited to continue to explore what perovskites can do. Enabling these devices to withstand water and heat is a big step towards being able to buy a perovskite device at a local hardware store.
Source: By Rebecca Palmer, Energy Frontier Research Centers

Read more: Teaching perovskites to swim

Major Expansion Plans Announced for Tesla


Tesla Charging I download
IN BRIEF

Tesla will double the number of its Superchargers and Destination Charging connectors in urban centers and on long distance routes in 2017. This is part of the company’s ongoing commitment to clean energy.

DOUBLING TESLA’S CHARGING NETWORK

On the heels of announcements about a more affordable Model 3 and a Tesla pickup truck, Tesla has begun to prepare for the mass-market in earnest for the first time by making more charging stations for available for their vehicles. To that end, Tesla’s blog announced on Monday, April 24, that the company would be doubling the Tesla charging network in 2017. This includes expanding existing sites in city centers and along highways so drivers need never wait to charge before getting back on the road.

Tesla Charging II download

Since the charging network began in 2012, Tesla has constructed more than 5,400 Superchargers to make long distance travel possible and even convenient for Tesla owners. They’ve also built more than 9,000 Destination Charging connectors equipped with Wall Connectors at restaurants, hotels, and other locations.

Via Tesla
Credit: Tesla

 

 

 

 

 

 

 

By the end of 2017 Tesla plans to have more than 10,000 Superchargers and 15,000 Destination Chargers in place around the world. Superchargers will increase by 150 percent in North America, and 1,000 additional Superchargers will be built in California alone. Site selection is underway now so many will open before summer travel season begins. Tesla will place charging sites in urban centers for quicker charging. Larger sites, which will accommodate simultaneous charging for several dozen drivers, will be constructed along the most-used travel routes for Tesla drivers.

NEW AGE IN ENERGY

Tesla’s investment in infrastructure represents a vote of confidence in the success of its newest products as well as the potential for the auto industry to continue shifting toward electric vehicles. Tesla’s overall plan is to change the way we think about power and energy. Experts are already acknowledging that Tesla will be disrupting the auto industry, and the energy industry is next.

The Tesla Revolution [INFOGRAPHIC]
Click to View Full Infographic

 

 

 

 

 

 

 

 

 

Tesla’s newest solar panels integrate seamlessly with the Tesla Powerwall battery system and will be available this summer. By 2018, the Tesla Gigafactory will reach full capacity; when it does, it will be producing more lithium ion batteries than the rest of the world combined. These tools will allow Tesla owners to power their homes — and their vehicles — with solar power, greatly reducing their carbon footprints.

With the ability to harness and store enough renewable energy, we could end our reliance on fossil fuels once and for all — and Musk thinks that’s something Earth urgently needs.

MIT: Cheap – Solar Cells – On Paper



Prof. Karen Gleason has come up with a low-cost, environmentally friendly way to make solar cells on ordinary tracing paper. Photo: Len RubensteinSpring 2012

Solar Cells on Paper

Chemical engineer Karen K. Gleason would like to paper the world with solar cells. Glued to laptops, tacked onto roof tiles, tucked into pockets, lining window shades, she envisions ultrathin, ultra-flexible solar cells going where no solar cells have gone before.

Silvery blue solar cells seem to magically generate electricity from sunlight the way Rumpelstiltskin spun straw into gold but in their present form, they’re more akin to gold than straw. 


Karen Gleason develops a low-cost, environmentally friendly way to make solar cells on tracing paper, which one day might charge a cell phone.




The cost of manufacturing crystalline and thin-film solar cells with silicon, glass, and rare earth materials like tellurium and indium is high.


LEARN MORE

MIT’s New Paper Chase: Cheap – Paper Solar Cells

Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering, has collaborated with Vladimir Bulovic, professor of electrical engineering; former chemical engineering graduate student Miles C. Barr; and others to come up with a low-cost, environmentally friendly way to make practically indestructible solar cells on ordinary tracing paper. 


One day, a paper solar cell might help us charge a cell phone. “A paper substrate is a thousand times cheaper than silicon and glass. What’s more, these solar cells can be scrunched up, folded a thousand times, and weatherproofed,” she says.

Using abundant, inexpensive organic elements like carbon, oxygen, and copper­­ — “nothing exotic,” she says — in a vacuum chamber, layers are “printed” through a process called vapor deposition, similar to frost forming on a window. At less than 120 degrees Celsius, the method is gentler and cooler than that normally used to manufacture photovoltaic materials, allowing it to be used on delicate paper, cloth, or plastic. “We repeat that five times and you end up with a solar cell,” she says; tweaking the composition of the five layers of materials determines the cells’ energy output. 

The research is funded by MITEI founding member Eni SpA, Italy’s biggest energy company, which is pursuing new advances in biofuels, solar, and other forms of alternative energy.

“The challenge of the project appealed to me,” she says. “I also thought it would be fun.” Her students display a prototype solar cell (a sheet of paper embossed with a pinstripe and chain-link design) folded into a paper airplane as a power source for an LCD clock. 
Gleason would like to see the first commercial solar paper devices hit the market in five years, but first the cells’ efficiency has to be ramped up from nearly 4 percent to at least 10 percent. (Commercial solar cells have an efficiency of around 15 percent.) MIT engineers believe this is doable

Then, the sky’s the limit — solar cells could power iPads, generate lighting inside tents, keep ski clothing toasty. 

“The paper cells’ portability could have a big impact in developing countries, where the cost of transporting solar cells has been prohibitive.

“Rather than confining solar power to rooftops or solar farms, paper photovoltaics can be used virtually anywhere, making energy ubiquitous,” Gleason says.

DOE: One small change makes Quantum Dot solar cells more efficient



The quest for more efficient solar cells has led to the search of new materials. For years, scientists have explored using tiny drops of designer materials, called quantum dots.




Now, we know that adding small amounts of manganese decreases the ability of quantum dots to absorb light but increases the current produced by an average of 300%. Under certain conditions, the current produced increased by 700%.

The enhancement is due to the faster rate that the electrons move from the quantum dot to the balance of the solar cell (what the scientists call the electron tunneling rate) in the presence of the manganese atoms at the interface.

Importantly, this observation is confirmed by theory, opening up possibilities for applying this approach to other systems (Applied Physics Letters, “Giant photocurrent enhancement by transition metal doping in quantum dot sensitized solar cells”).

The power conversion efficiency of quantum dot solar cells has reached about 12%. However, the overall efficiency of quantum dot solar cells is relatively low compared to photovoltaic systems in use today that are based on silicon. In addition, quantum dot solar cells are not as efficient as emerging next-generation solar cells.

The results obtained in this work point to a surprisingly straightforward alternative route. Scientists can significantly improve the performance of this family of solar cells by adding small amounts of alternate metals.

In the quest to replace more traditional solar materials, such as silicon, with more efficient and high-performing options, scientists have been studying quantum dot solar cells as an alternative to harvest sunlight for conversion to electricity.

In this solar cell design, quantum dots are used as the material that absorbs sunlight and converts it to electricity. Quantum dots are very small, nanometer-sized, particles, whose solar conversion properties, in this case a characteristic gap in the energy levels of the electrons called the “bandgap,” are tunable by changing the size or chemical composition.

This is in contrast to bulk materials whose bandgap is fixed by the chemical composition or choice of material(s) alone. This size dependence of bandgap makes quantum dots attractive for multi-junction solar cells, whose efficiency is enhanced by using a variety of materials that absorb different parts of the “rainbow” of wavelengths of light found in the solar spectrum.

This research team discovered that adding small amounts of the transition metal manganese (Mn), or “doping,” resulted in a huge enhancement in the efficiency rate of changing light to electricity for lead sulfide (PbS) quantum dot sensitized solar cells.

Relatively small concentrations of Mn (4 atomic percent) cause the current to increase by an average of 300% with a maximum increase of up to 700%.

Moreover, the mechanism by which this occurs cannot be explained by the light absorption alone because both the experimental and theoretical absorption spectra demonstrate a several times decrease in the absorption coefficient on the addition of Mn.

The team proposes that the dramatic increase is due to a mechanism of increased electron tunneling through the atom pairs at the quantum dot interface with the next layer of the solar cell.

The team used ab initio calculations, which is a computational approach that can describe new phenomena without the need to fit or extrapolate experimental data, to confirm this mechanism.

While typical doping approaches focus on improving exciton lifetime and light absorption channels, results obtained in this study provide an alternative route for significant improvement on the efficiency of quantum dot sensitized solar cells.

Source: U.S. Department of Energy, Office of Science

Experts Outline Pathway for Generating Up to Ten (10) Terawatts of Power from Sunlight by 2030: NREL – GA SERI


NREL IV energy-resources-renewables-fossil-fuel-uranium

The annual potential of solar energy far exceeds the world’s energy consumption, but the goal of using the sun to provide a significant fraction of global electricity demand is far from being realized.

Scientists from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), their counterparts from similar institutes in Japan and Germany, along with researchers at universities and industry, assessed the recent trajectory of photovoltaics and outlined a potential worldwide pathway to produce a significant portion of the world’s electricity from solar power in the new Science paper, Terawatt-Scale Photovoltaics: Trajectories and Challenges.NREL I download

Fifty-seven experts met in Germany in March 2016 for a gathering of the Global Alliance of Solar Energy Research Institutes (GA-SERI), where they discussed what policy initiatives and technology advances are needed to support significant expansion of solar power over the next couple of decades.

“When we came together, there was a consensus that the global PV industry is on a clear trajectory to reach the multi-terawatt scale over the next decade,” said lead author Nancy Haegel, director of NREL’s Materials Science Center. “However, reaching the full potential for PV technology in the global energy economy will require continued advances in science and technology. Bringing the global research community together to solve challenges related to realizing this goal is a key step in that direction.”

NREL III pv global

Photovoltaics (PV) generated about 1 percent of the total electricity produced globally in 2015 but also represented about 20 percent of new installation. The International Solar Alliance has set a target of having at least 3 terawatts – or 3,000 gigawatts (GW) – of additional solar power capacity by 2030, up from the current installed capacity of 71 GW. But even the most optimistic projections have under-represented the actual deployment of PV over the last decade, and the GA-SERI paper discusses a realistic trajectory to install 5-10 terawatts of PV capacity by 2030.

Reaching that figure should be achievable through continued technology improvements and cost decreases, as well as the continuation of incentive programs to defray upfront costs of PV systems, according to the Science paper, which in addition to Haegel was co-authored by David Feldman, Robert Margolis, William Tumas, Gregory Wilson, Michael Woodhouse, and Sarah Kurtz of NREL.

GA-SERI’s experts predict 5-10 terawatts of PV capacity could be in place by 2030 if these challenges can be overcome:

  • A continued reduction in the cost of PV while also improving the performance of solar modules
  • A drop in the cost of and time required to expand manufacturing and installation capacity
  • A move to more flexible grids that can handle high levels of PV through increased load shifting, energy storage, or transmission
  • An increase in demand for electricity by using more for transportation and heating or cooling
  • Continued progress in storage for energy generated by solar power.

The Fraunhofer Institute for Solar Energy (Germany), the National Institute of Advanced Industrial Science and Technology (Japan), and the National Renewable Energy Laboratory (United States) are the member institutes of GA-SERI, which was founded in 2012.

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.