Stanford scientists build the first all-carbon solar cell

Stanford Report, October 31, 2012

Researchers have developed a solar cell made entirely of carbon, an inexpensive substitute for the pricey materials used in conventional solar panels.

Stanford University scientists have built the first solar cell made entirely of carbon, a promising alternative to the expensive materials used in photovoltaic devices today. The results are published in today’s online edition of the journal ACS Nano.

“Carbon has the potential to deliver high performance at a low cost,” said study senior author Zhenan Bao, a professor of chemical engineering at Stanford.  “To the best of our knowledge, this is the first demonstration of a working solar cell that has all of the components made of carbon. This study builds on previous work done in our lab.”

Unlike rigid silicon solar panels that adorn many rooftops, Stanford’s thin film prototype is made of carbon materials that can be coated from solution. “Perhaps in the future we can look at alternative markets where flexible carbon solar cells are coated on the surface of buildings, on windows or on cars to generate electricity,” Bao said.

The coating technique also has the potential to reduce manufacturing costs, said Stanford graduate student Michael Vosgueritchian, co-lead author of the study with postdoctoral researcher Marc Ramuz.

“Processing silicon-based solar cells requires a lot of steps,” Vosgueritchian explained. “But our entire device can be built using simple coating methods that don’t require expensive tools and machines.”

Carbon nanomaterials

The Bao group’s experimental solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes.  In a typical thin film solar cell, the electrodes are made of conductive metals and indium tin oxide (ITO). “Materials like indium are scarce and becoming more expensive as the demand for solar cells, touchscreen panels and other electronic devices grows,” Bao said.  “Carbon, on the other hand, is low cost and Earth-abundant.”

Scientist's hand holding carbon solar cellThe Bao group’s all-carbon solar cell consists of a photoactive layer, which absorbs sunlight, sandwiched between two electrodes.

For the study, Bao and her colleagues replaced the silver and ITO used in conventional electrodes with graphene – sheets of carbon that are one atom thick –and single-walled carbon nanotubes that are 10,000 times narrower than a human hair. “Carbon nanotubes have extraordinary electrical conductivity and light-absorption properties,” Bao said.

For the active layer, the scientists used material made of carbon nanotubes and “buckyballs” – soccer ball-shaped carbon molecules just one nanometer in diameter.  The research team recently filed a patent for the entire device.

“Every component in our solar cell, from top to bottom, is made of carbon materials,” Vosgueritchian said. “Other groups have reported making all-carbon solar cells, but they were referring to just the active layer in the middle, not the electrodes.”

One drawback of the all-carbon prototype is that it primarily absorbs near-infrared wavelengths of light, contributing to a laboratory efficiency of less than 1 percent – much lower than commercially available solar cells.  “We clearly have a long way to go on efficiency,” Bao said.  “But with better materials and better processing techniques, we expect that the efficiency will go up quite dramatically.”

Improving efficiency

The Stanford team is looking at a variety of ways to improve efficiency. “Roughness can short-circuit the device and make it hard to collect the current,” Bao said. “We have to figure out how to make each layer very smooth by stacking the nanomaterials really well.”

The researchers are also experimenting with carbon nanomaterials that can absorb more light in a broader range of wavelengths, including the visible spectrum.

“Materials made of carbon are very robust,” Bao said. “They remain stable in air temperatures of nearly 1,100 degrees Fahrenheit.”

The ability of carbon solar cells to out-perform conventional devices under extreme conditions could overcome the need for greater efficiency, according to Vosgueritchian. “We believe that all-carbon solar cells could be used in extreme environments, such as at high temperatures or at high physical stress,” he said. “But obviously we want the highest efficiency possible and are working on ways to improve our device.”

“Photovoltaics will definitely be a very important source of power that we will tap into in the future,” Bao said. “We have a lot of available sunlight. We’ve got to figure out some way to use this natural resource that is given to us.”

Other authors of the study are Peng Wei of Stanford and Chenggong Wang and Yongli Gao of the University of Rochester Department of Physics and Astronomy. The research was funded by theGlobal Climate and Energy Project at Stanford and the Air Force Office for Scientific Research.

A Nano Way to Store Hydrogen

October / November 2012By: Tona KunzVolume 10 Number 5
A new type of nanoscale molecular trap makes it possible for industry to store large amounts of hydrogen in small fuel cells or capture, compact and remove volatile radioactive gas from spent nuclear fuel in an affordable, easily commercialized way.

The ability to adjust the size of the trap openings to select for specific molecules or to alter how molecules are released at industrially accessible pressures makes the trap uniquely versatile.  The trap is constructed of commercially available material and made possible through collaborative work at Argonne and Sandia national laboratories.

“This introduces a new class of materials to nuclear waste remediation,” said Tina Nenoff, a Sandia chemist. “This design can capture and retain about five times more iodine that current material technologies.”

Organic molecules linked together with metal ions in a molecular-scale Tinker Toy-like lattice called a metal-organic-framework, or MOF, form the trap. Molecules of radioactive iodine or carbon dioxide or even hydrogen for use as fuel can enter through windows in the framework.
Once pressure is applied, these windows are distorted, preventing the molecules from leaving.  This creates a cage and a way of selecting what to trap based on the molecule’s shape and size.
The compression also turns the MOF from a fluffy molecular sponge taking up a lot of space into a compact pellet.  The ability to compress large amounts of gas into small volumes is a crucial step to developing hydrogen gas as an alternative fuel for engines.

But what makes this MOF, called ZIF-8, dramatically different from designs created during the past decade is its ability to distort the windows in the framework and trap large volumes of gas at relatively low pressures. ZIF-8 takes about twice the pressure of a junkyard car compactor, which is about 10 times less pressure than is needed to compress other comparable zeolite MOFs.

This creates an environmentally friendly process that is within the reach of existing industrial machinery, can be produced on a large scale, and is financially viable.

The ZIF-8 is composed of zinc cations and organic imidazolate-based linkers. The topology of the framework is analogous to sodalite – a well-known zeolite.

The use of other available porous MOFs is limited to small batches because specialized scientific equipment is needed to apply the large amount of pressure they require to compress to a position that will maintain the new shape that traps the gas. This makes them not commercially viable.

Chapman and her colleagues at Argonne used X-rays from the Advanced Photon Source to perfect the low-pressure technique of making the MOFs into dense pellets. The distortion of the molecular framework that occurs during the process does not significantly reduce the gas storage capacity.

“These MOFs have wide-reaching applications,” said Karena Chapman, an Argonne scientist, who was inspired to explore low-pressure treatments for MOFs by her experiences working with flexible MOFs for hydrogen storage. Prior to this work, most high –pressure science research, such as the development of MOFs, took its cue from earth studies were extensive pressures cause transitions in geological materials.

With the pellet process worked out, the scientists tapped Nenoff at Sandia, to find a just the right type of molecule for the MOF’s structure to expand its use from hydrogen and carbon dioxide capture. Nenoff and her team had identified the ZIF-8 MOF as being ideally suited to separate and trap radioactive iodine molecules from a stream of spent nuclear fuel based on its pore size and high surface area.

This marks one of the first attempts to use MOFs in this way.  This presents opportunities for cleaning up nuclear reactor accidents and for reprocessing fuel.  Countries such as France, Russia and India recover fissile materials from radioactive components in used nuclear fuel to provide fresh fuel for power plants. This reduces the amount of nuclear waste that must be stored.  Radioactive iodine has a half-life of 16 million years.

The research team is continuing to look at different MOF structures to increase the amount of iodine storage and better predict how environmental conditions such as humidity will affect the storage lifetime.

Tona Kunz is a writer at Argonne National Laboratory.

Learn the future predictions on nanotechnology

A doorway to the future of nanotechnology

*** Note to Readers: We have re-posted this information from ‘Motion Perpetual’. We will be following future posts and will continue to re-post with timely topics and information. Cheers!   – BWH –



Scientists have discovered that certain materials develop completely new properties when sized at a nanometer. This has created immense potential for creating completely new materials from existing ones. Scientists made future prediction about nanotechnology showing hope that this technology would create a number of new devices and material in future and those new creations would be applied in a number of fields such as biomaterials, medicine, electronics and energy generation. Due to its immense potential, governments of the different major countries have invested billion dollars in nanotechnology researches. Our site upholds the scientific debate regarding the future implications of this new found technology. We believe in offering people with the most authentic and detailed scientific articles by proficient writers.

What future predictions do scientists make about nanotechnology?

The future prediction attaches much importance to molecular nanotechnology in the 21st century. Also it says that in the days to come a shift is likely to occur from ‘passive’ nanotechnology to ‘active’ nanotechnology. In the future decades, machines using nanotechnology are likely to become more complex; i.e. in place of mere crystals, particles, rods, tubes or atom sheets you will then have machines with motors, valves, pumps, switches etc. Another significant nanotechnology future prediction is related to the generation of nanomaterials. In the recent times, the procedure for the generation or production of nanomaterials results in huge amounts of waste and very little material and is also a very costly procedure. But scientists are hopeful that in the near future this nanomaterial manufacturing procedure can definitely be bettered and made cost-effective. Through our site visitors can learn the future of this revolutionary scientific discovery and its impact on human life. We aim at educating people with true in-depth knowledge.

The future prediction made by scientists with regard to applying nanotechnology in the medical field kindles new flame of hope for cancer patients, patients with nervous system dysfunctions, multiple sclerosis, spinal cord injuries. Even surgeries are likely to be made possible through nanotechnology.

Scientists also predict that in the near future nanotechnology is going to be applied in nanoelectronic devices consisting of nano wires, carbon nano sized tubes. Those devices would be high performance devices running on hybrid molecular theory of electronics. It could be your favorite computer or transistor or any other electronic device. Scientists think that the use of nanoelectronic devices will increase in Medical Diagnostics.

The potentially world-changing research that no one knows about

Foresight Nanotech Institute Logo


Imagine that there exists a two-dimensional (single-layer) crystal that is made of a commonly available element, is stronger than steel yet lighter weight and flexible, displays ballistic electron mobility (for comparison, two orders of magnitude greater mobility than silicon, at room temperature), and is sufficiently optically active to see with the naked eye (though far more practically, using an optical microscope). Prospective applications include flexible, high-speed electronic devices and new composite materials for aircraft.


Would this sound like a potentially world-changing substance worthy of scientific attention and funding?

That substance is graphene, a single layer of graphite with hexagonally arranged carbon atoms (visualized as chicken wire).


Now imagine that the mechanical properties of this substance aren’t measured yet, as was the case for graphene before 2009. Imagine further that there is no way to grow or isolate the single-layer crystals in their free state, as was the case for graphene before 2004. Stepping back in time yet further, imagine that the theoretical work predicting massless charge carrier behavior hasn’t been carried out yet, as was the case for graphene before 1984.


Peeling back these milestones, we can see that if the scientific question being asked is “What can be realized from here?” then the graphene timeline played out characteristically, with major advancements coming primarily from opportunity-based research. In other words, over 50+ years, from the initial theoretical work on graphene in 1947 until stable monolayers were achieved in 2004, there was limited vision of what end-goals might be achievable and limited drive to get there.


What happens when a different question is asked, specifically “What can be realized according to physical law?” This is the key premise of the exploratory engineering approach, a methodology proposed by Eric Drexler for assessing the capabilities of future technologies. He points out, for example, that the principles of space flight had been worked out long before science and industry advanced enough to get to actual launch.


For initial space flight development, the answers to the two questions above were dramatically different: what could be done in practice was far behind what had been established as theoretically possible, and there was no defined path between them. By identifying what was achievable according to physical law, the longer-term goal of space flight entered the consciousness of physicists, engineers, and politicians, bringing great minds and great resources to the challenge.


With the benefit of similarly future-focused knowledge, perhaps graphene might have received far more attention far sooner. Consider this: the groundbreaking experimental work that sparked the field as we know it today was the discovery that single-layer graphene could be extracted from a piece of graphite by (essentially) pressing cellophane tape against it and peeling it away. In other words, a decades-long roadblock to achievements in graphene research was not a matter of inadequate supporting technology but one of limited scientific attention.


Here graphene serves as a useful illustration of how progress could potentially be hindered when opportunity-based research is relied upon exclusively. Scientific advancement could benefit significantly from deliberate, exploratory engineering. Perhaps there are numerous other ‘graphenes’ right now, going unnoticed or under-prioritized, because we are failing to ask: what can be realized according to physical law?


English: Graphene layer. Français : Couche de ...


Scientists demonstrate high-efficiency quantum dot solar cells


Research shows newly developed solar powered cells may soon outperform conventional photovoltaic technology. Scientists from the National Renewable Energy Laboratory (NREL) have demonstrated the first solar cell with external quantum efficiency (EQE) exceeding 100 percent for photons with energies in the solar range. (The EQE is the percentage of photons that get converted into electrons within the device.) The researchers will present their findings at the AVS 59th International Symposium and Exhibition, held Oct. 28 — Nov. 2, in Tampa, Fla.

While traditional semiconductors only produce one electron from each photon, nanometer-sized crystalline materials such as quantum dots avoid this restriction and are being developed as promising photovoltaic materials. An increase in the efficiency comes from quantum dots harvesting energy that would otherwise be lost as heat in conventional semiconductors. The amount of heat loss is reduced and the resulting energy is funneled into creating more electrical current.

By harnessing the power of a process called multiple exciton generation (MEG), the researchers were able to show that on average, each blue photon absorbed can generate up to 30 percent more current than conventional technology allows. MEG works by efficiently splitting and using a greater portion of the energy in the higher-energy photons. The researchers demonstrated an EQE value of 114 percent for 3.5 eV photons, proving the feasibility of this concept in a working device.

Joseph Luther, a senior scientist at NREL, believes MEG technology is the right direction. “Since current solar cell technology is still too expensive to completely compete with non-renewable energy sources, this technology employing MEG demonstrates that the way in which scientists and engineers think about converting solar photons to electricity is constantly changing,” Luther said. “There may be a chance to dramatically increase the efficiency of a module, which could result in solar panels that are much cheaper than non-renewable energy sources.”


Quantum Dots Promise to Significantly Boost Photovoltaic Efficiencies


In the sometimes strange world of nanoscale materials, unexpected things can happen. This is exactly what scientists at the National Renewable Energy Laboratory (NREL) have discovered while exploring quantum dots (QDs). These semiconductor nanocrystals typically have diameters from about 2 to 10 nanometers (nm, or one billionth of a meter) and contain only hundreds to thousands of atoms. But they could do great things when it comes to generating electricity.


Semiconductor quantum dots used in so-called “third-generation” solar cells have the potential to dramatically increase—in some cases even double—the efficiency of converting sunlight to electricity. The conversion process works via “multiple exciton generation (MEG).”

In this process, when a single photon of light of sufficient energy is absorbed by the quantum dot, it produces more than one bound electron-hole pair, or exciton. NREL scientists were the first to predict this important unusual MEG effect in QDs, which contrasts with conventional photovoltaic (PV) cells having much larger crystals and many more atoms and in which one photon produces only one electron-hole pair. The electronic process is also very fast, occurring within 200 femtoseconds—or 200 million billionths (10-15) of a second.

To Read the Full Article, Go Here:





Solar Panel Makers Need Equipment Upgrades to Survive Shakeout

With overcapacity of 82%, companies need innovative tools to differentiate from cheaper Chinese rivals, says Lux Research.

English: Thin-film PV array

English: Thin-film PV array (Photo credit: Wikipedia)

BOSTON, Oct 25, 2012 (BUSINESS WIRE) — Reeling from a glut of production capacity, makers of solar panels need to acquire innovative production equipment in order to cut costs, increase margins, and offer differentiated products, according to Lux Research.

This year, global capacity utilization is at 55% for crystalline silicon (x-Si) module production, 70% for cadmium telluride (CdTe) and 80% for copper indium gallium (di) selenide (CIGS). Consequently, cell and module manufacturers are turning to core product differentiation to revamp margins and fend off low-cost Chinese competition.

“Across the industry there is recognition that innovation is needed to survive a shakeout,” said Fatima Toor, Lux Research Analyst and the lead author of the report titled, “Turning Lemons into Lemonade: Opportunities in the Turbulent Photovoltaic Equipment Market.” “Equipment suppliers have a vital role to play in enabling that innovation.”

Lux Research analysts examined the PV production equipment landscape to identify opportunities for innovation. Among their findings:

— There’s opportunity in reducing silicon costs. Current wafer sawing techniques waste silicon; in contrast, technologies, such as direct solidification and epitaxial silicon eliminate the need for wafer sawing. Emerging quasi-monocrystalline silicon (qc-Si) ingot growth enables 40% cheaper c-Si wafers.

— In CIGS, standardization is key. CIGS thin-film PV relies on custom equipment today. However, off-the-shelf tools and improved throughput will drive higher efficiencies, performance and yield – lowering capex and helping manufacturers attain scale and competitive production costs.

— New cell designs lead to equipment upgrades. Emerging cell designs, such as selective emitter (SE) and heterojunction with intrinsic thin layer (HIT) present potential for high efficiencies. However, they require new tools, and as a result, 60% to 70% of new equipment sales are for the cell production equipment.

The report, titled “Turning Lemons into Lemonade: Opportunities in the Turbulent Photovoltaic Equipment Market,” is part of the Lux Research Solar Components Intelligence service.

About Lux Research

Lux Research provides strategic advice and on-going intelligence for emerging technologies. Leaders in business, finance and government rely on us to help them make informed strategic decisions. Through our unique research approach focused on primary research and our extensive global network, we deliver insight, connections and competitive advantage to our clients. Visit for more information.

SOURCE: Lux Research

Note To Readers: We have been following a ‘disruptive nanotechnology’ company, researching and developing a ‘3rd Generation’ of solar cells based in part on low-cost quantum dots and reduced input cost printing techniques. Below is a short excerpt from a website, a link also provided below. Perhaps, with innovation such as this, the U.S. Solar industry can become the clear leader in providing grid competitive renewable energy. Perhaps ….        Cheers!  – BWH-

Solterra Renewable Technologies

“Solterra will be producing and distributing a Thin Film Quantum Dot PV Solar Cell which is differentiated from other PV cells by a unique technology that results in lower cost, higher efficiency, and broader spectral performance.  Solterra’s Quantum Dot Solar Cell achieves a dramatically lower manufacturing cost per watt because no vacuum equipment is required, no expensive silicon is required and low-cost screen printing and/or inkjet techniques are used on inexpensive substrates. Secondly, the Solterra Thin Film Quantum Dot Solar Cell has the potential to generate multiple excitons from each proton providing the potential for exponential improvements in conversion efficiency. Third, Solterra’s PV cell is not only more efficient in the early morning and late afternoon compared to crystalline silicon PV cells, but it also has the potential to harvest light energy in the infrared and ultraviolet spectra.


Nanorods could improve LED displays: Cornell

Oct. 24, 2012

Well-ordered nanorods could improve LED displays

Scientists have utilized the imaging capabilities of the Cornell High Energy Synchrotron Source (CHESS) to help develop enhanced light-emitting diode displays using bottom-up engineering methods.

Collaborative work between researchers from the University of Florida and CHESS has resulted in a novel way to make colloidal “superparticles” from oriented nanorods of semiconducting materials. The work was published in the journal Science, Oct. 19.

The team synthesized nanorods with a cadmium selenide and cadmium sulfide shell. Taking advantage of the compounds’ lattice mismatch interfaces, they assembled these rods into larger periodic colloidal structures, called superparticles.

The superparticles exhibit enhanced light emission and polarization, features that are important for fabrication of LED televisions and computer screens. The nucleated superparticles can further be cast into macroscopic polarized films. The films could increase efficiency in polarized LED television and computer screen by as much as 50 percent, the researchers say.

The team, which included CHESS scientist Zhongwu Wang, made use of the CHESS facility to collect small angle X-ray scattering data from specimens inside tiny diamond-anvil cells. They used this technique, in combination with high-resolution transmission electron microscopy, to analyze how nanorods with attached organic components could be formed into well-ordered structures.

The nanorods first align within a layer as hexagonally ordered arrays. Then the highly ordered nanorod arrays behave like a series of layered units, self-assembling into structures that exhibit long-range order as they grow into large superparticles. The elongated superparticles can be aligned in a polymer matrix into macroscopic films.

The project demonstrates how scientists are learning to recognize and exploit anisotropic interactions between nanorods, which can be adjusted during the synthesis process, to create single-domain, needle-like particles. The authors hope their work can lead to new processes of self-assembly to create nano-objects with other anisotropic shapes, perhaps even joining two or more types of objects to form well-defined mesoscopic and macroscopic architectures with greater and greater complexity.

The team was led by Charles Cao, professor of chemistry at the University of Florida. The lead author of the paper was Tie Wang of Cao’s group.

Lockheed Martin Advanced Technology Center Develops Revolutionary Nanotechnology Copper Solder

PALO ALTO, Calif., October 24, 2012 – Scientists in the Advanced Materials and Nanosystems directorate at the Lockheed Martin Space Systems Advanced Technology Center (ATC) in Palo Alto have developed a revolutionary nanotechnology copper-based electrical interconnect material, or solder, that can be processed around 200 °C. Once fully optimized, the CuantumFuse™ solder material is expected to produce joints with up to 10 times the electrical and thermal conductivity compared to tin-based materials currently in use. Applications in military and commercial systems are currently under consideration.

“We are enormously excited about our CuantumFuse™ breakthrough, and are very pleased with the progress we’re making to bring it to full maturity,” said Dr. Kenneth Washington, vice president of the ATC. “We pride ourselves on providing innovations like CuantumFuse™ for space and defense applications, but in this case we are excited about the enormous potential of CuantumFuse™ in defense and commercial manufacturing applications.”

In the past, nearly all solders contained lead, but there is now an urgent need for lead-free solder because of a worldwide effort to phase out hazardous materials in electronics. The European Union implemented lead-free solder in 2006. The State of California did so on January 1, 2007, followed soon thereafter by New Jersey and New York City.

The principal lead-free replacement – a combination of tin, silver and copper (Sn/Ag/Cu) – has proven acceptable to the consumer electronics industry that deals mostly with short product life cycles and relatively benign operating environments. However, multiple issues have arisen: high processing temperatures drive higher cost, the high tin content can lead to tin whiskers that can cause short circuits, and fractures are common in challenging environments, making it difficult to quantify reliability. These reliability concerns are particularly acute in systems for the military, aerospace, medical, oil and gas, and automotive industries. In such applications, long service life and robustness of components are critical, where vibration, shock, thermal cycling, humidity, and extreme temperature use can be common.

“To address these concerns, we realized a fundamentally new approach was needed to solve the lead-free solder challenge,” said Dr. Alfred Zinn, materials scientist at the ATC and inventor of CuantumFuse™ solder. “Rather than finding another multi-component alloy, our team devised a solution based on the well-known melting point depression of materials in nanoparticle form. Given this nanoscale phenomenon, we’ve produced a solder paste based on pure copper.”

A number of requirements were addressed in the development of the CuantumFuse™ solder paste including, but not limited to: 1) sufficiently small nanoparticle size, 2) a reasonable size distribution, 3) reaction scalability, 4) low cost synthesis, 5) oxidation and growth resistance at ambient conditions, and 6) robust particle fusion when subjected to elevated temperature. Copper was chosen because it is already used throughout the electronics industry as a trace, interconnect, and pad material, minimizing compatibility issues. It is cheap (1/4th the cost of tin; 1/100th the cost of silver, and 1/10,000th that of gold), abundant, and has 10 times the electrical and thermal conductivity compared to commercial tin-based solder.

The ATC has demonstrated CuantumFuse™ with the assembly of a small test camera board. “These accomplishments are extremely exciting and promising, but we still have to solve a number of technical challenges before CuantumFuse™ will be ready for routine use in military and commercial applications,” said Mike Beck, director of the Advanced Materials and Nanosystems group at the ATC. Solving these challenges, such as improving bond strength, is the focus on the group’s ongoing research and development.

The ATC is the research and development organization of Lockheed Martin Space Systems Company (LMSSC) and is engaged in the research, development, and transition of technologies in phenomenology & sensors, optics & electro-optics, laser radar, RF & photonics, guidance & navigation, space science & instrumentation, advanced materials & nanosystems, thermal sciences & cryogenics, and modeling, simulation & information science.

LMSSC, a major operating unit of Lockheed Martin Corporation, designs and develops, tests, manufactures and operates a full spectrum of advanced-technology systems for national security and military, civil government and commercial customers. Chief products include human space flight systems; a full range of remote sensing, navigation, meteorological and communications satellites and instruments; space observatories and interplanetary spacecraft; laser radar; ballistic missiles; missile defense systems; and nanotechnology research and development.

Headquartered in Bethesda, Md., Lockheed Martin is a global security and aerospace company that employs about 120,000 people worldwide and is principally engaged in the research, design, development, manufacture, integration and sustainment of advanced technology systems, products and services. The corporation’s net sales for 2011 were $46.5 billion.

‘Quantum dot’ solar cells offer bright future with reliable, low cost energy

London, July 30 (ANI): Researchers have made a breakthrough in the development of colloidal quantum dot (CQD) films, leading to the most efficient CQD solar cell ever.

Researchers from the University of Toronto (U of T) and King Abdullah University of Science and Technology (KAUST) created a solar cell out of inexpensive materials that was certified at a world-record 7.0 percent efficiency.

“Previously, quantum dot solar cells have been limited by the large internal surface areas of the nanoparticles in the film, which made extracting electricity difficult,” said Dr. Susanna Thon, a lead co-author of the paper.

“Our breakthrough was to use a combination of organic and inorganic chemistry to completely cover all of the exposed surfaces,” Dr. Thon stated.

Quantum dots are semiconductors only a few nanometres in size and can be used to harvest electricity from the entire solarspectrum – including both visible and invisible wavelengths. Unlike current slow and expensive semiconductor growth techniques, CQD films can be created quickly and at low cost, similar to paint or ink.

The researchers, led by U of T Engineering Professor Ted Sargent, paves the way for solar cells that can be fabricated on flexible substrates in the same way newspapers are rapidly printed in mass quantities.

The U of T cell represents a 37 percent increase in efficiency over the previous certified record. In order to improve efficiency, the researchers needed a way to both reduce the number of “traps” for electrons associated with poor surface quality while simultaneously ensuring their films were very dense to absorb as much light as possible. The solution was a so-called “hybrid passivation” scheme.

“By introducing small chlorine atoms immediately after synthesizing the dots, we’re able to patch the previously unreachable nooks and crannies that lead to electron traps. We follow that by using short organic linkers to bind quantum dots in the film closer together,” explained doctoral student and lead co-author Alex Ip.

Work led by Professor Aram Amassian of KAUST showed that the organic ligand exchange was necessary to achieve the densest film.

“The KAUST group used state-of-the-art synchrotron methods with sub-nanometer resolution to discern the structure of the films and prove that the hybrid passivation method led to the densest films with the closest-packed nanoparticles,” stated Professor Amassian.

The advance opens up many avenues for further research and improvement of device efficiencies, which could contribute to a bright future with reliable, low cost solar energy.

Their work featured in a letter published in Nature Nanotechnology. (ANI)