Tag Archives: solar cells

Solar cells from the University of Alberta?

Trevor Robb’s Aug. 7, 2015 article for the Edmonton Sun (Alberta, Canada) features a research team dedicated to producing better solar cells and a facility (nanoFAB) at the University of Alberta,

But in an energy rich province like Alberta — known for its oil and gas sector — [JIllian] Buriak [chemistry professor at the University of Alberta, Canada Research chair of nanomaterials] is on a mission to shed some light on another form of energy Alberta is known for, solar energy.

So her team is dedicated to producing flexible, recyclable plastic solar cells that can be printed just like a newspaper.

In fact, they’ve already begun doing so.

In order to produce the sheet-like solar cells, Buriak and her team use nothing more than simple commercial laminators and a spray gun, not unlike something you would use to paint a car.

“We run them through this laminator that squeezes them down and turns them from something that’s not conducting to something that’s really conducting,” said Buriak.

“You could incorporate it into clothing, you could incorporate it into books, into window blinds, or unroll it on a tent when you’re camping,” said Buriak. “You could use it anywhere. Anything from simple funny things to cafe umbrellas that could allow you to charge electronic devices, to large scale things in developing countries; large scale solar cells that you could simply carry on your backpack, unroll at a medical clinic, and suddenly you have instant power.”

There are more details about Buriak’s work and information about nanoFAB in Robb’s article. As for technical information, the best I can find is in an Aug. 29, 2013 University of Alberta news release (also on EurekAlert),

University of Alberta researchers have found that abundant materials in the Earth’s crust can be used to make inexpensive and easily manufactured nanoparticle-based solar cells.

The discovery, several years in the making, is an important step forward in making solar power more accessible to parts of the world that are off the traditional electricity grid or face high power costs, such as the Canadian North, said researcher Jillian Buriak, a chemistry professor and senior research officer of the National Institute for Nanotechnology based on the U of A campus.
Buriak and her team have designed nanoparticles that absorb light and conduct electricity from two very common elements: phosphorus and zinc. Both materials are more plentiful than scarce materials such as cadmium and are free from manufacturing restrictions imposed on lead-based nanoparticles.

Buriak collaborated with U of A post-doctoral fellows Erik Luber of the U of A Faculty of Engineering and Hosnay Mobarok of the Faculty of Science to create the nanoparticles. The team was able to develop a synthetic method to make zinc phosphide nanoparticles, and demonstrated that the particles can be dissolved to form an ink and processed to make thin films that are responsive to light.

Buriak and her team are now experimenting with the nanoparticles, spray-coating them onto large solar cells to test their efficiency. The team has applied for a provisional patent and has secured funding to enable the next step to scale up manufacture.

I wonder if this news article by Robb is an attempt by Buriak to attract interest from potential investors?

Perovskite, nanorods, and solar energy

As the authors, Azhar Fakharuddin, Rajan Jose, and Thomas Brown, note in an Aug. 7, 2015 Nanowerk Spotlight article , securing energy sources is a global pursuit and pervoskite (a new wonder material for solar cells) has presented a challenge (Note: A link has been removed),

Energy security has been a top global concern motivating researchers to seek it from renewable and cost-effective resources. Solar cells, that convert sun light into electricity, hold the promise as a cheap energy alternative. The silicon and thin film photovoltaic industry have taken many strides to lower energy prices; however, continued research is required in order to extensively compete with fossil fuels.

The development of perovskite solar cells, first reported in 2009 (and with a record power conversion efficiency of 20.1 percent so far), is a possible route towards high efficiency photovoltaics that are also cost-effectiveness, owing to to their easy-processing from solution.

Question marks have however remained on their stability.

The authors (members of a research team) have recently published a paper about a method that could make perovskite solar cells more stable,

Now, a research team from University Malaysia Pahang, focussing on renewable energy, working in in collaboration with scientists from University of Rome ‘Tor Vergata’, Italy, has developed the world’s first nanorod-based perovskite solar module.

Among the three types of electron transport layers investigated, the nanorod-based devices retained the original efficiency values even after 2500 hours of shelf-life investigation, a protocol used to gauge initial stability and indoor lifetime performance.
The device employing a conventional TiO2 nanoparticle material showed nearly 60% of original performance, whereas planar devices employing a compact TiO2 layer showed below 5% of original performance, measured at similar experimental conditions.
A chemical analysis of the devices hinted that the peculiar conformation of nanorods facilitates a stable perovskite phase due to their inherent stability and macroporous nature.

If you want more detail, the research team’s Nanowerk Spotlight article is the place to look (it’s almost like a Reddit session except there’s no ‘ask me anything’ option). There’s also the team’s paper,

Vertical TiO2 Nanorods as a Medium for Stable and High-Efficiency Perovskite Solar Modules by Azhar Fakharuddin, Francesco Di Giacomo, Alessandro L. Palma, Fabio Matteocci, Irfan Ahmed, Stefano Razza, Alessandra D’Epifanio, Silvia Licoccia, Jamil Ismail, Aldo Di Carlo, Thomas M. Brown, and Rajan Jose. ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b03265 Publication Date (Web): July 24, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

One final note, I’ve been meaning to publish a post about perovskite-based solar cells for a while now as the material seems to be sweeping the solar energy community and, now, it’s done.

Saving silver; a new kind of electrode

An Aug. 1, 2015 news item on Nanotechnology Now highlights work from Germany’s Helmholtz-Zentrum Berlin für Materialien und Energie (Helmholtz Zentrum Berlin),

The electrodes for connections on the “sunny side” of a solar cell need to be not just electrically conductive, but transparent as well. As a result, electrodes are currently made either by using thin strips of silver in the form of a coarse-meshed grid squeegeed onto a surface, or by applying a transparent layer of electrically conductive indium tin oxide (ITO) compound. Neither of these are ideal solutions, however. This is because silver is a precious metal and relatively expensive, and silver particles with nanoscale dimensions oxidise particularly rapidly; meanwhile, indium is one of the rarest elements on earth crust and probably will only continue to be available for a few more years.

Manuela Göbelt on the team of Prof. Silke Christiansen has now developed an elegant new solution using only a fraction of the silver and entirely devoid of indium to produce a technologically intriguing electrode. The doctoral student initially made a suspension of silver nanowires in ethanol using wet-chemistry techniques. She then transferred this suspension with a pipette onto a substrate, in this case a silicon solar cell. As the solvent is evaporated, the silver nanowires organise themselves into a loose mesh that remains transparent, yet dense enough to form uninterrupted current paths.

A July 31, 2015 Helmholtz Zentrum Berlin press release (also on EurekAlert), which originated the news item, describes the work in more detail,

Subsequently, Göbelt used an atomic layer deposition technique to gradually apply a coating of a highly doped wide bandgap semiconductor known as AZO. AZO consists of zinc oxide that is doped with aluminium. It is much less expensive than ITO and just as transparent, but not quite as electrically conductive. This process caused tiny AZO crystals to form on the silver nanowires, enveloped them completely, and finally filled in the interstices. The silver nanowires, measuring about 120 nanometres in diameter, were covered with a layer of about 100 nanometres of AZO and encapsulated by this process.

Quality map calculated

Measurements of the electrical conductivity showed that the newly developed composite electrode is comparable to a conventional silver grid electrode. However, its performance depends on how well the nanowires are interconnected, which is a function of the wire lengths and the concentration of silver nanowires in the suspension. The scientists were able to specify the degree of networking in advance with computers. Using specially developed image analysis algorithms, they could evaluate images taken with a scanning electron microscope and predict the electrical conductivity of the electrodes from them.

“We are investigating where a given continuous conductive path of nanowires is interrupted to see where the network is not yet optimum”, explains Ralf Keding. Even with high-performance computers, it still initially took nearly five days to calculate a good “quality map” of the electrode. The software is now being optimised to reduce the computation time. “The image analysis has given us valuable clues about where we need to concentrate our efforts to increase the performance of the electrode, such as increased networking to improve areas of poor coverage by changing the wire lengths or the wire concentration in solution”, says Göbelt.

Practical aternative to conventional electrodes

“We have developed a practical, cost-effective alternative to conventional screen-printed grid electrodes and to the common ITO type that is threatened however by material bottlenecks”, says Christiansen, who heads the Institute of Nanoarchitectures for Energy Conversion at HZB and additionally directs a project team at the Max Planck Institute for the Science of Light (MPL).

Only a fraction of silver, nearly no shadow effects

The new electrodes can actually be made using only 0.3 grams of silver per square metre, while conventional silver grid electrodes require closer to between 15 and 20 grams of silver. In addition, the new electrode casts a considerably smaller shadow on the solar cell. “The network of silver nanowires is so fine that almost no light for solar energy conversion is lost in the cell due to the shadow”, explains Göbelt. On the contrary, she hopes “it might even be possible for the silver nanowires to scatter light into the solar cell absorbers in a controlled fashion through what are known as plasmonic effects.”

Here’s a link to and a citation for the paper,

Encapsulation of silver nanowire networks by atomic layer deposition for indium-free transparent electrodes by Manuela Göbelt, Ralf Keding, Sebastian W. Schmitt, Björn Hoffmann, Sara Jäckle, Michael Latzel, Vuk V. Radmilović, Velimir R. Radmilović,  Erdmann Spiecker, and Silke Christiansen. Nano Energy Volume 16, September 2015, Pages 196–206 doi:10.1016/j.nanoen.2015.06.027

This paper is behind a paywall.

Sea sapphires: now you see them, now you don’t and more about structural colour/color

The structural colour of the sea sapphire

 Scientists are studying the disappearing act of this ocean-dwelling copepod. Credit: Kaj Maney, www.liquidguru.com Courtesy: American Chemical Society

Scientists are studying the disappearing act of this ocean-dwelling copepod.
Credit: Kaj Maney, www.liquidguru.com Courtesy: American Chemical Society

Now, you’ve seen a sea sapphire. Here’s more about them and the interest they hold for experts in photonics, from a July 15, 2015 news item on ScienceDaily,

Sapphirina, or sea sapphire, has been called “the most beautiful animal you’ve never seen,” and it could be one of the most magical. Some of the tiny, little-known copepods appear to flash in and out of brilliantly colored blue, violet or red existence. Now scientists are figuring out the trick to their hues and their invisibility. The findings appear in the Journal of the American Chemical Society and could inspire the next generation of optical technologies.

A July 15, 2015 American Chemical Society (ACS) news release, which originated the news item, provides more detail,

Copepods are tiny aquatic crustaceans that live in both fresh and salt water. Some males of the ocean-dwelling Sapphirina genus display striking, iridescent colors that scientists think play a role in communication and mate recognition. The shimmering animals’ colors result when light bounces off of the thin, hexagonal crystal plates that cover their backs. These plates also help them vanish, if only fleetingly. Scientists didn’t know specifically what factors contributed to creating different shades. Scientists at the Weizmann Institute [Israel] and the Interuniversity Institute for Marine Sciences in Eilat [Israel] wanted to investigate the matter.

The researchers measured the light reflectance — which determines color — of live Sapphirina males and the spacing between crystal layers. They found that changes of reflectance depended on the thickness of the spacing. And for at least one particular species, when light hits an animal at a 45-degree angle, reflectance shifts out of the visible light range and into the ultraviolet, and it practically disappears. Their results could help inform the design of artificial photonic crystal structures, which have many potential uses in reflective coatings, optical mirrors and optical displays.

To sum this up, the colour and the invisibility properties are due to thin, hexagonal crystal plates and the spacing of these plates, in other words, structural colour, which is usually achieved at the nanoscale.

Here’s a link to and a citation for the paper,

Structural Basis for the Brilliant Colors of the Sapphirinid Copepods by Dvir Gur, Ben Leshem, Maria Pierantoni, Viviana Farstey, Dan Oron, Steve Weiner, and Lia Addadi. J. Am. Chem. Soc., 2015, 137 (26), pp 8408–8411 DOI: 10.1021/jacs.5b05289 Publication Date (Web): June 22, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

For anyone who’s interested, Lynn Kimlicka has a nice explanation of structural colour in a July 22, 2015 posting on the Something About Science blog where she discusses some recent research iridescence in bird feathers and synthetic melanin. She also shares a picture of her budgie and its iridescent feathers. The ‘melanin’ research was mentioned here in a May 19, 2015 posting where I also provide a link to a great 2013 piece on structural throughout the animal and plant kingdoms by Cristina Luiggi for The Scientist.

Understanding how nanostructures can affect optical properties could be leading to new ways of managing light. A July 23, 2015 news item on ScienceDaily describes a project at the University of Delaware dedicated to “changing the color of light,”

Researchers at the University of Delaware have received a $1 million grant from the W.M. Keck Foundation to explore a new idea that could improve solar cells, medical imaging and even cancer treatments. Simply put, they want to change the color of light.

A July 23, 2015 University of Delaware (UD) news release, which originated the news item, provides more information about the proposed research,

“A ray of light contains millions and millions of individual units of light called photons,” says project leader Matthew Doty. “The energy of each photon is directly related to the color of the light — a photon of red light has less energy than a photon of blue light. You can’t simply turn a red photon into a blue one, but you can combine the energy from two or more red photons to make one blue photon.”

This process, called “photon upconversion,” isn’t new, Doty says. However, the UD team’s approach to it is.

They want to design a new kind of semiconductor nanostructure that will act like a ratchet. It will absorb two red photons, one after the other, to push an electron into an excited state when it can emit a single high-energy (blue) photon.

These nanostructures will be so teeny they can only be viewed when magnified a million times under a high-powered electron microscope.

“Think of the electrons in this structure as if they were at a water park,” Doty says. “The first red photon has only enough energy to push an electron half-way up the ladder of the water slide. The second red photon pushes it the rest of the way up. Then the electron goes down the slide, releasing all of that energy in a single process, with the emission of the blue photon. The trick is to make sure the electron doesn’t slip down the ladder before the second photon arrives. The semiconductor ratchet structure is how we trap the electron in the middle of the ladder until the second photon arrives to push it the rest of the way up.”

The UD team will develop new semiconductor structures containing multiple layers of different materials, such as aluminum arsenide and gallium bismuth arsenide, each only a few nanometers thick. This “tailored landscape” will control the flow of electrons into states with varying potential energy, turning once-wasted photons into useful energy.

The UD team has shown theoretically that their semiconductors could reach an upconversion efficiency of 86 percent, which would be a vast improvement over the 36 percent efficiency demonstrated by today’s best materials. What’s more, Doty says, the amount of light absorbed and energy emitted by the structures could be customized for a variety of applications, from lightbulbs to laser-guided surgery.

How do you even begin to make structures so tiny they can only be seen with an electron microscope? In one technique the UD team will use, called molecular beam epitaxy, nanostructures will be built by depositing layers of atoms one at a time. Each structure will be tested to see how well it absorbs and emits light, and the results will be used to tailor the structure to improve performance.

The researchers also will develop a milk-like solution filled with millions of identical individual nanoparticles, each one containing multiple layers of different materials. The multiple layers of this structure, like multiple candy shells in an M&M, will implement the photon ratchet idea. Through such work, the team envisions a future upconversion “paint” that could be easily applied to solar cells, windows and other commercial products.

Improving medical tests and treatments

While the initial focus of the three-year project will be on improving solar energy harvesting, the team also will explore biomedical applications.

A number of diagnostic tests and medical treatments, ranging from CT [computed tomography] and PET [positron emission tomography] scans to chemotherapy, rely on the release of fluorescent dyes and pharmaceutical drugs. Ideally, such payloads are delivered both at specific disease sites and at specific times, but this is hard to control in practice.

The UD team aims to develop an upconversion nanoparticle that can be triggered by light to release its payload. The goal is to achieve the controlled release of drug therapies even deep within diseased human tissue while reducing the peripheral damage to normal tissue by minimizing the laser power required.

“This is high-risk, high-reward research,” Doty says. “High-risk because we don’t yet have proof-of-concept data. High-reward because it has such a huge potential impact in renewable energy to medicine. It’s amazing to think that this same technology could be used to harvest more solar energy and to treat cancer. We’re excited to get started!”

That’s it for structural colour/color today.

Spray-on solar cells from the University of Toronto (Canada)

It’s been a while since there’s been a solar cell story from the University of Toronto (U of T) and I was starting to wonder if Ted (Edward) Sargent had moved to another educational institution. The drought has ended with the announcement of three research papers being published by researchers from Sargent’s U of T laboratory. From a Dec. 5, 2014 ScienceDaily news item,

Pretty soon, powering your tablet could be as simple as wrapping it in cling wrap.

That’s Illan Kramer’s … hope. Kramer and colleagues have just invented a new way to spray solar cells onto flexible surfaces using miniscule light-sensitive materials known as colloidal quantum dots (CQDs) — a major step toward making spray-on solar cells easy and cheap to manufacture.

A Dec. 4, 2014 University of Toronto news release (also on EurekAlert) by Marit Mitchell, which originated the news item, gives a bit more detail about the technology (Note: Links have been removed),

 Solar-sensitive CQDs printed onto a flexible film could be used to coat all kinds of weirdly-shaped surfaces, from patio furniture to an airplane’s wing. A surface the size of a car roof wrapped with CQD-coated film would produce enough energy to power three 100-watt light bulbs – or 24 compact fluorescents.

He calls his system sprayLD, a play on the manufacturing process called ALD, short for atomic layer deposition, in which materials are laid down on a surface one atom-thickness at a time.

Until now, it was only possible to incorporate light-sensitive CQDs onto surfaces through batch processing – an inefficient, slow and expensive assembly-line approach to chemical coating. SprayLD blasts a liquid containing CQDs directly onto flexible surfaces, such as film or plastic, like printing a newspaper by applying ink onto a roll of paper. This roll-to-roll coating method makes incorporating solar cells into existing manufacturing processes much simpler. In two recent papers in the journals Advanced Materials and Applied Physics Letters, Kramer showed that the sprayLD method can be used on flexible materials without any major loss in solar-cell efficiency.

Kramer built his sprayLD device using parts that are readily available and rather affordable – he sourced a spray nozzle used in steel mills to cool steel with a fine mist of water, and a few regular air brushes from an art store.

“This is something you can build in a Junkyard Wars fashion, which is basically how we did it,” says Kramer. “We think of this as a no-compromise solution for shifting from batch processing to roll-to-roll.”

“As quantum dot solar technology advances rapidly in performance, it’s important to determine how to scale them and make this new class of solar technologies manufacturable,” said Professor Ted Sargent, vice-dean, research in the Faculty of Applied Science & Engineering at University of Toronto and Kramer’s supervisor. “We were thrilled when this attractively-manufacturable spray-coating process also led to superior performance devices showing improved control and purity.”

In a third paper in the journal ACS Nano, Kramer and his colleagues used IBM’s BlueGeneQ supercomputer to model how and why the sprayed CQDs perform just as well as – and in some cases better than – their batch-processed counterparts. This work was supported by the IBM Canada Research and Development Centre, and by King Abdullah University of Science and Technology.

For those who would like to see the sprayLD device,

Here are links and citation for all three papers,

Efficient Spray-Coated Colloidal Quantum Dot Solar Cells by Illan J. Kramer, James C. Minor, Gabriel Moreno-Bautista, Lisa Rollny, Pongsakorn Kanjanaboos, Damir Kopilovic, Susanna M. Thon, Graham H. Carey, Kang Wei Chou, David Zhitomirsky, Aram Amassian, and Edward H. Sargent. Advanced Materials DOI: 10.1002/adma.201403281 Article first published online: 10 NOV 2014

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Colloidal quantum dot solar cells on curved and flexible substrates by Illan J. Kramer, Gabriel Moreno-Bautista, James C. Minor, Damir Kopilovic, and Edward H. Sargent. Appl. Phys. Lett. 105, 163902 (2014); http://dx.doi.org/10.1063/1.4898635 Published online 21 October 2014

© 2014 AIP Publishing LLC

Electronically Active Impurities in Colloidal Quantum Dot Solids by Graham H. Carey, Illan J. Kramer, Pongsakorn Kanjanaboos, Gabriel Moreno-Bautista, Oleksandr Voznyy, Lisa Rollny, Joel A. Tang, Sjoerd Hoogland, and Edward H. Sargent. ACS Nano, 2014, 8 (11), pp 11763–11769 DOI: 10.1021/nn505343e Publication Date (Web): November 6, 2014

Copyright © 2014 American Chemical Society

All three papers are behind paywalls.

Given the publication dates for the papers, this looks like an attempt to get some previously announced research noticed by sending out a summary news release using a new ‘hook’ to get attention. I hope it works for them as it must be disheartening to have your research sink into obscurity because the announcements were issued during one or more busy news cycles.

One final note, if I understand the news release correctly, this work is still largely theoretical as there don’t seem to have been any field tests.

A multiferroic material for more powerful solar cells

A Nov. 12, 2014 INRS (Institut national de la recherche scientifique; Université du Québec) news release (also on EurekAlert), describes new work on solar cells from Federico Rosei’s laboratory (Note: Links have been removed; A French language version of the news release can be found here),

Applying a thin film of metallic oxide significantly boosts the performance of solar panel cells—as recentlydemonstrated by Professor Federico Rosei and his team at the Énergie Matériaux Télécommunications Research Centre at Institut national de la recherche scientifique (INRS). The researchers have developed a new class of materials comprising elements such as bismuth, iron, chromium, and oxygen. These“multiferroic” materials absorb solar radiation and possess unique electrical and magnetic properties. This makes them highly promising for solar technology, and also potentially useful in devices like electronic sensors and flash memory drives. …

The INRS research team discovered that by changing the conditions under which a thin film of these materials is applied, the wavelengths of light that are absorbed can be controlled. A triple-layer coating of these materials—barely 200 nanometres thick—captures different wavelengths of light. This coating converts much more light into electricity than previous trials conducted with a single layer of the same material. With a conversion efficiency of 8.1% reported by [Riad] Nechache and his coauthors, this is a major breakthrough in the field.

The team currently envisions adding this coating to traditional single-crystal silicon solar cells (currently available on the market). They believe it could increase maximum solar efficiency by 18% to 24% while also boosting cell longevity. As this technology draws on a simplified structure and processes, as well as abundant and stable materials, new photovoltaic (PV) cells will be more powerful and cost less. This means that the INRS team’s breakthrough may make it possible to reposition silicon PV cells at the forefront of the highly competitive solar energy market.

Here’s a link to and a citation for the paper,

Bandgap tuning of multiferroic oxide solar cells by R. Nechache, C. Harnagea, S. Li, L. Cardenas, W. Huang,  J. Chakrabartty, & F. Rosei. Nature Photonics (2014) doi:10.1038/nphoton.2014.255 Published online
10 November 2014

This paper is behind a paywall although there is a free preview via ReadCube Access.

I last mentioned Federico Rose in a March 4, 2014 post about a talk (The exploration of the role of nanoscience in tomorrow’s energy solutions) he was giving in Vancouver (Canada).

Solar cells and ‘tinkertoys’

A Nov. 3, 2014 news item on Nanowerk features a project researchers hope will improve photovoltaic efficiency and make solar cells competitive with other sources of energy,

 Researchers at Sandia National Laboratories have received a $1.2 million award from the U.S. Department of Energy’s SunShot Initiative to develop a technique that they believe will significantly improve the efficiencies of photovoltaic materials and help make solar electricity cost-competitive with other sources of energy.

The work builds on Sandia’s recent successes with metal-organic framework (MOF) materials by combining them with dye-sensitized solar cells (DSSC).

“A lot of people are working with DSSCs, but we think our expertise with MOFs gives us a tool that others don’t have,” said Sandia’s Erik Spoerke, a materials scientist with a long history of solar cell exploration at the labs.

A Nov. 3, 2014 Sandia National Laboratories news release, which originated the news item, describes the project and the technology in more detail,

Sandia’s project is funded through SunShot’s Next Generation Photovoltaic Technologies III program, which sponsors projects that apply promising basic materials science that has been proven at the materials properties level to demonstrate photovoltaic conversion improvements to address or exceed SunShot goals.

The SunShot Initiative is a collaborative national effort that aggressively drives innovation with the aim of making solar energy fully cost-competitive with traditional energy sources before the end of the decade. Through SunShot, the Energy Department supports efforts by private companies, universities and national laboratories to drive down the cost of solar electricity to 6 cents per kilowatt-hour.

DSSCs provide basis for future advancements in solar electricity production

Dye-sensitized solar cells, invented in the 1980s, use dyes designed to efficiently absorb light in the solar spectrum. The dye is mated with a semiconductor, typically titanium dioxide, that facilitates conversion of the energy in the optically excited dye into usable electrical current.

DSSCs are considered a significant advancement in photovoltaic technology since they separate the various processes of generating current from a solar cell. Michael Grätzel, a professor at the École Polytechnique Fédérale de Lausanne in Switzerland, was awarded the 2010 Millennium Technology Prize for inventing the first high-efficiency DSSC.

“If you don’t have everything in the DSSC dependent on everything else, it’s a lot easier to optimize your photovoltaic device in the most flexible and effective way,” explained Sandia senior scientist Mark Allendorf. DSSCs, for example, can capture more of the sun’s energy than silicon-based solar cells by using varied or multiple dyes and also can use different molecular systems, Allendorf said.

“It becomes almost modular in terms of the cell’s components, all of which contribute to making electricity out of sunlight more efficiently,” said Spoerke.

MOFs’ structure, versatility and porosity help overcome DSSC limitations

Though a source of optimism for the solar research community, DSSCs possess certain challenges that the Sandia research team thinks can be overcome by combining them with MOFs.

Allendorf said researchers hope to use the ordered structure and versatile chemistry of MOFs to help the dyes in DSSCs absorb more solar light, which he says is a fundamental limit on their efficiency.

“Our hypothesis is that we can put a thin layer of MOF on top of the titanium dioxide, thus enabling us to order the dye in exactly the way we want it,” Allendorf explained. That, he said, should avoid the efficiency-decreasing problem of dye aggregation, since the dye would then be locked into the MOF’s crystalline structure.

MOFs are highly-ordered materials that also offer high levels of porosity, said Allendorf, a MOF expert and 29-year veteran of Sandia. He calls the materials “Tinkertoys for chemists” because of the ease with which new structures can be envisioned and assembled. [emphasis mine]

Allendorf said the unique porosity of MOFs will allow researchers to add a second dye, placed into the pores of the MOF, that will cover additional parts of the solar spectrum that weren’t covered with the initial dye. Finally, he and Spoerke are convinced that MOFs can help improve the overall electron charge and flow of the solar cell, which currently faces instability issues.

“Essentially, we believe MOFs can help to more effectively organize the electronic and nano-structure of the molecules in the solar cell,” said Spoerke. “This can go a long way toward improving the efficiency and stability of these assembled devices.”

In addition to the Sandia team, the project includes researchers at the University of Colorado-Boulder, particularly Steve George, an expert in a thin film technology known as atomic layer deposition.

The technique, said Spoerke, is important in that it offers a pathway for highly controlled materials chemistry with potentially low-cost manufacturing of the DSSC/MOF process.

“With the combination of MOFs, dye-sensitized solar cells and atomic layer deposition, we think we can figure out how to control all of the key cell interfaces and material elements in a way that’s never been done before,” said Spoerke. “That’s what makes this project exciting.”

Here’s a picture showing an early Tinkertoy set,

Original Tinkertoy, Giant Engineer #155. Questor Education Products Co., c.1950 [downloaded from http://en.wikipedia.org/wiki/Tinkertoy#mediaviewer/File:Tinkertoy_300126232168.JPG]

Original Tinkertoy, Giant Engineer #155. Questor Education Products Co., c.1950 [downloaded from http://en.wikipedia.org/wiki/Tinkertoy#mediaviewer/File:Tinkertoy_300126232168.JPG]

The Tinkertoy entry on Wikipedia has this,

The Tinkertoy Construction Set is a toy construction set for children. It was created in 1914—six years after the Frank Hornby’s Meccano sets—by Charles H. Pajeau and Robert Pettit and Gordon Tinker in Evanston, Illinois. Pajeau, a stonemason, designed the toy after seeing children play with sticks and empty spools of thread. He and Pettit set out to market a toy that would allow and inspire children to use their imaginations. At first, this did not go well, but after a year or two over a million were sold.

Shrinky Dinks, tinkertoys, Lego have all been mentioned here in conjunction with lab work. I’m always delighted to see scientists working with or using children’s toys as inspiration of one type or another.

Fishnet of gold atoms improves solar cell performance

Apparently they’re calling the University of Western Ontario by a new name, Western University. Given the university’s location in what is generally acknowledged as central Canada or, sometimes, as eastern Canada, this seems like a geographically confusing approach not only in Canada but elsewhere too. After all, more than one country boasts a ‘west’.

A Sept. 26, 2014 news item on Nanowerk highlights new work on improving solar cell performance (Note: A link has been removed),

Scientists at Western University [Ontario, Canada] have discovered that a small molecule created with just 144 atoms of gold can increase solar cell performance by more than 10 per cent. These findings, published recently by the high-impact journal Nanoscale (“Tessellated gold nanostructures from Au144(SCH2CH2Ph)60 molecular precursors and their use in organic solar cell enhancement”), represent a game-changing innovation that holds the potential to take solar power mainstream and dramatically decrease the world’s dependence on traditional, resource-based sources of energy, says Giovanni Fanchini from Western’s Faculty of Science.

For those of us who remember ‘times tables’, the number 144 can have a special meaning as it is the last number (’12’ times ’12’ equals ‘144’) one was obliged to memorize. At least, that was true at my school in Vancouver, Canada but perhaps not elsewhere, eh?

Getting back to the ‘fishnet’, a Sept. 25, 2014 Western University news release, which originated the news item, expands the business possibilities for this work,

Fanchini, the Canada Research Chair in Carbon-based Nanomaterials and Nano-optoelectronics, says the new technology could easily be fast-tracked and integrated into prototypes of solar panels in one to two years and solar-powered phones in as little as five years.

“Every time you recharge your cell phone, you have to plug it in,” says Fanchini, an assistant professor in Western’s Department of Physics and Astronomy. “What if you could charge mobile devices like phones, tablets or laptops on the go? Not only would it be convenient, but the potential energy savings would be significant.”

The Western researchers have already started working with manufacturers of solar components to integrate their findings into existing solar cell technology and are excited about the potential.

“The Canadian business industry already has tremendous know-how in solar manufacturing,” says Fanchini. “Our invention is modular, an add-on to the existing production process, so we anticipate a working prototype very quickly.”

The news release then gives a few technical details,

Making nanoplasmonic enhancements, Fanchini and his team use “gold nanoclusters” as building blocks to create a flexible network of antennae on more traditional solar panels to attract an increase of light. While nanotechnology is the science of creating functional systems at the molecular level, nanoplasmonics investigates the interaction of light with and within these systems.

“Picture an extremely delicate fishnet of gold,” explains Fanchini explains, noting that the antennae are so miniscule they are unseen even with a conventional optical microscope. “The fishnet catches the light emitted by the sun and draws it into the active region of the solar cell.”

According to Fanchini, the spectrum of light reflected by gold is centered on the yellow colour and matches the light spectrum of the sun making it superior for such antennae as it greatly amplifies the amount of sunlight going directly into the device.

“Gold is very robust, resilient to oxidization and not easily damaged, making it the perfect material for long-term use,” says Fanchini. “And gold can also be recycled.”

It has been known for some time that larger gold nanoparticles enhance solar cell performance, but the Western team is getting results with “a ridiculously small amount” – approximately 10,000 times less than previous studies, which is 10,000 times less expensive too.

I hope to hear about a working prototype soon. Meanwhile, here’s a link to and a citation for the paper,

Tessellated gold nanostructures from Au144(SCH2CH2Ph)60 molecular precursors and their use in organic solar cell enhancement by Reg Bauld, Mahdi Hesari, Mark S. Workentin, and Giovanni Fanchini. Nanoscale, 2014,6, 7570-7575 DOI: 10.1039/C4NR01821D
First published online 06 May 2014

This paper is behind a paywall.

One final comment, it seems like a long lead time between publication of the paper and publicity. I wonder if the paper failed to get notice in May 2014, assuming there was a campaign at the time, or if this is considered a more optimal time period for getting noticed.

Wearable solar panels with perovskite

There was a bit of a flutter online in late July 2014 about solar cell research and perovskite, a material that could replace silicon therefore making solar cells more affordable, which hopefully would lead to greater adoption of the technology. Happily, the publishers of the study seem to have reissued their news release (h/t Aug. 11, 2014 news item on Nanwerk).

From the Wiley online press release Nr. 29/2014,

Textile solar cells are an ideal power source for small electronic devices incorporated into clothing. In the journal Angewandte Chemie, Chinese scientists have now introduced novel solar cells in the form of fibers that can be woven into a textile. The flexible, coaxial cells are based on a perovskite material and carbon nanotubes; they stand out due to their excellent energy conversion efficiency of 3.3 % and their low production cost.

The dilemma for solar cells: they are either inexpensive and inefficient, or they have a reasonable efficiency and are very expensive. One solution may come from solar cells made of perovskite materials, which are less expensive than silicon and do not require any expensive additives. Perovskites are materials with a special crystal structure that is like that of perovskite, a calcium titanate. These structures are often semiconductors and absorb light relatively efficiently. Most importantly, they can move electrons excited by light for long distances within the crystal lattice before they return to their energetic ground state and take up a solid position – a property that is very important in solar cells.

A team led by Hisheng Peng at Fudan University in Shanghai has now developed perovskite solar cells in the form of flexible fibers that can be woven into electronic textiles. Their production process is relatively simple and inexpensive because it uses a solution-based process to build up the layers.

The anode is a fine stainless steel wire coated with a compact n-semiconducting titanium dioxide layer. A layer of porous nanocrystalline titanium dioxide is deposited on top of this. This provides a large surface area for the subsequent deposition of the perovskite material CH3NH3PbI3. This is followed by a layer made of a special organic material. Finally a transparent layer of aligned carbon nanotubes is continuously wound over the whole thing to act as the cathode. The resulting fiber is so fine and flexible that it can be woven into textiles.

The perovskite layer absorbs light, that excites electrons and sets them free, causing a charge separation between the electrons and the formally positively charged “holes” The electrons enter the conducting band of the compact titanium dioxide layer and move to the anode. The “holes” are captured by the organic layer. The large surface area and the high electrical conductivity of the carbon nanotube cathode aid in the rapid conduction of the charges with high photoelectric currents. The fiber solar cell can attain an energy conversion efficiency of 3.3 %, exceeding that of all previous coaxial fiber solar cells made with either dyes or polymers.

Here’s an image used in the press release illustrating the new fiber,

[downloaded from http://www.wiley-vch.de/vch/journals/2002/press/201429press.pdf]

[downloaded from http://www.wiley-vch.de/vch/journals/2002/press/201429press.pdf]

Here’s a link to and a citation for the paper,

Integrating Perovskite Solar Cells into a Flexible Fiber by Longbin Qiu, Jue Deng, Xin Lu, Zhibin Yang, and Prof. Huisheng Peng. Angewandte Chemie International Edition DOI: 10.1002/anie.201404973 Article first published online: 22 JUL 2014

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

I found a second item about perovskite and solar cells in a May 16, 2014 article by Vicki Marshall for Chemistry World which discussed some research in the UK (Note: Links have been removed),

A lead-free and non-toxic alternative to current perovskite solar-cell technology has been reported by researchers in the UK: tin halide perovskite solar cells. They are also cheaper to manufacture than the silicon solar cells currently dominating the market.

Nakita Noel, part of Henry Snaith’s research team at the University of Oxford, describes how perovskite materials have caused a bit of a whirlwind since they came out in 2009: ‘Everybody that’s working in the solar community is looking to beat silicon.’ Despite the high efficiency of conventional crystalline silicon solar cells (around 20%), high production and installation costs decrease their economic feasibility and widespread use.

The challenge to find a cheaper alternative led to the development of perovskite-based solar cells, as organic–inorganic metal trihalide perovskites have both abundant and cheap starting materials. However, the presence of lead in some semiconductors could create toxicology issues in the future. As Noel puts it ‘every conference you present at somebody is bound to put up their hand and ask “What about the lead – isn’t this toxic?”’

Brian Hardin, co-founder of PLANT PV, US, and an expert in new materials for photovoltaic cells, says the study ‘should be considered a seminal work on alternative perovskites and is extremely valuable to the field as they look to better understand how changes in chemistry affect solar cell performance and stability.’

Here’s a link to and a citation for the UK researchers’ paper,

Lead-free organic–inorganic tin halide perovskites for photovoltaic applications by Nakita K. Noel, Samuel D. Stranks, Antonio Abate, Christian Wehrenfennig, Simone Guarnera, Amir-Abbas Haghighirad, Aditya Sadhana, Giles E. Eperon, Sandeep K. Pathak, Michael B. Johnston, Annamaria Petrozza, Laura M. Herza, and Henry J. Snaith. Energy Environ. Sci., 2014, Advance Article DOI: 10.1039/C4EE01076K First published online 01 May 2014

This article was open access until June 27, 2014 but now it is behind a paywall.

I notice there’s no mention of lead in the materials describing the research paper from the Chinese scientists. Perhaps they were working with lead-free materials.

Sandia National Laboratories looking for commercial partners to bring titanium dioxide nanoparticles (5 nm in diameter) to market

Sandia National Laboratories (Sandia Labs) doesn’t  ask directly but I think the call for partners is more than heavily implied. Let’s start with a June 17, 2014 news item on ScienceDaily,

Sandia National Laboratories has come up with an inexpensive way to synthesize titanium-dioxide nanoparticles and is seeking partners who can demonstrate the process at industrial scale for everything from solar cells to light-emitting diodes (LEDs).

Titanium-dioxide (TiO2) nanoparticles show great promise as fillers to tune the refractive index of anti-reflective coatings on signs and optical encapsulants for LEDs, solar cells and other optical devices. Optical encapsulants are coverings or coatings, usually made of silicone, that protect a device.

Industry has largely shunned TiO2 nanoparticles because they’ve been difficult and expensive to make, and current methods produce particles that are too large.

Sandia became interested in TiO2 for optical encapsulants because of its work on LED materials for solid-state lighting.

Current production methods for TiO2 often require high-temperature processing or costly surfactants — molecules that bind to something to make it soluble in another material, like dish soap does with fat.

Those methods produce less-than-ideal nanoparticles that are very expensive, can vary widely in size and show significant particle clumping, called agglomeration.

Sandia’s technique, on the other hand, uses readily available, low-cost materials and results in nanoparticles that are small, roughly uniform in size and don’t clump.

“We wanted something that was low cost and scalable, and that made particles that were very small,” said researcher Todd Monson, who along with principal investigator Dale Huber patented the process in mid-2011 as “High-yield synthesis of brookite TiO2 nanoparticles.” [emphases mine]

A June 17, 2014 Sandia Labs news release, which originated the news item, goes on to describe the technology (Note: Links have been removed),

Their (Monson and Huber) method produces nanoparticles roughly 5 nanometers in diameter, approximately 100 times smaller than the wavelength of visible light, so there’s little light scattering, Monson said.

“That’s the advantage of nanoparticles — not just nanoparticles, but small nanoparticles,” he said.

Scattering decreases the amount of light transmission. Less scattering also can help extract more light, in the case of an LED, or capture more light, in the case of a solar cell.

TiO2 can increase the refractive index of materials, such as silicone in lenses or optical encapsulants. Refractive index is the ability of material to bend light. Eyeglass lenses, for example, have a high refractive index.

Practical nanoparticles must be able to handle different surfactants so they’re soluble in a wide range of solvents. Different applications require different solvents for processing.

“If someone wants to use TiO2 nanoparticles in a range of different polymers and applications, it’s convenient to have your particles be suspension-stable in a wide range of solvents as well,” Monson said. “Some biological applications may require stability in aqueous-based solvents, so it could be very useful to have surfactants available that can make the particles stable in water.”

The researchers came up with their synthesis technique by pooling their backgrounds — Huber’s expertise in nanoparticle synthesis and polymer chemistry and Monson’s knowledge of materials physics. The work was done under a Laboratory Directed Research and Development project Huber began in 2005.

“The original project goals were to investigate the basic science of nanoparticle dispersions, but when this synthesis was developed near the end of the project, the commercial applications were obvious,” Huber said. The researchers subsequently refined the process to make particles easier to manufacture.

Existing synthesis methods for TiO2 particles were too costly and difficult to scale up production. In addition, chemical suppliers ship titanium-dioxide nanoparticles dried and without surfactants, so particles clump together and are impossible to break up. “Then you no longer have the properties you want,” Monson said.

The researchers tried various types of alcohol as an inexpensive solvent to see if they could get a common titanium source, titanium isopropoxide, to react with water and alcohol.

The biggest challenge, Monson said, was figuring out how to control the reaction, since adding water to titanium isopropoxide most often results in a fast reaction that produces large chunks of TiO2, rather than nanoparticles. “So the trick was to control the reaction by controlling the addition of water to that reaction,” he said.

Some textbooks dismissed the titanium isopropoxide-water-alcohol method as a way of making TiO2 nanoparticles. Huber and Monson, however, persisted until they discovered how to add water very slowly by putting it into a dilute solution of alcohol. “As we tweaked the synthesis conditions, we were able to synthesize nanoparticles,” Monson said.

Whoever wrote the news release now makes the plea which isn’t quite a plea (Note: A link has been removed),

The next step is to demonstrate synthesis at an industrial scale, which will require a commercial partner. Monson, who presented the work at Sandia’s fall Science and Technology Showcase, said Sandia has received inquiries from companies interested in commercializing the technology.

“Here at Sandia we’re not set up to produce the particles on a commercial scale,” he said. “We want them to pick it up and run with it and start producing these on a wide enough scale to sell to the end user.”

Sandia would synthesize a small number of particles, then work with a partner company to form composites and evaluate them to see if they can be used as better encapsulants for LEDs, flexible high-index refraction composites for lenses or solar concentrators. “I think it can meet quite a few needs,” Monson said.

I wish them good luck.