28 Jul 2015
Photographs of upconversion in a cuvette containing cadmium selenide/rubrene mixture. The yellow spot is emission from the rubrene originating from (a) an unfocused continuous wave 800 nm laser with an intensity of 300 W/cm2. (b) a focused continuous wave 980 nm laser with an intensity of 2000 W/cm2. The photographs, taken with an iPhone 5, were not modified in any way.
When it comes to installing solar cells, labor cost and the cost of the land to house them constitute the bulk of the expense. The solar cells — made often of silicon or cadmium telluride — rarely cost more than 20 percent of the total cost. Solar energy could be made cheaper if less land had to be purchased to accommodate solar panels, best achieved if each solar cell could be coaxed to generate more power.
A huge gain in this direction has now been made by a team of chemists at the University of California, Riverside that has found an ingenious way to make solar energy conversion more efficient. The researchers report in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in “upconverting” photons in the visible and near-infrared regions of the solar spectrum.
“The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today’s solar cells,” explained Christopher Bardeen, a professor of chemistry. The research was a collaborative effort between him and Ming Lee Tang, an assistant professor of chemistry. “This is energy lost, no matter how good your solar cell. The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity, then adds their energies together to make one higher energy photon. This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted.”
Bardeen added that these materials are essentially “reshaping the solar spectrum” so that it better matches the photovoltaic materials used today in solar cells. The ability to utilize the infrared portion of the solar spectrum could boost solar photovoltaic efficiencies by 30 percent or more.
In their experiments, Bardeen and Tang worked with cadmium selenide and lead selenide semiconductor nanocrystals. The organic compounds they used to prepare the hybrids were diphenylanthracene and rubrene. The cadmium selenide nanocrystals could convert visible wavelengths to ultraviolet photons, while the lead selenide nanocrystals could convert near-infrared photons to visible photons.
In lab experiments, the researchers directed 980-nanometer infrared light at the hybrid material, which then generated upconverted orange/yellow fluorescent 550-nanometer light, almost doubling the energy of the incoming photons. The researchers were able to boost the upconversion process by up to three orders of magnitude by coating the cadmium selenide nanocrystals with organic ligands, providing a route to higher efficiencies.
“This 550 — nanometer light can be absorbed by any solar cell material,” Bardeen said. “The key to this research is the hybrid composite material — combining inorganic semiconductor nanoparticles with organic compounds. Organic compounds cannot absorb in the infrared but are good at combining two lower energy photons to a higher energy photon. By using a hybrid material, the inorganic component absorbs two photons and passes their energy on to the organic component for combination. The organic compounds then produce one high-energy photon. Put simply, the inorganics in the composite material take light in; the organics get light out.”
Besides solar energy, the ability to upconvert two low energy photons into one high energy photon has potential applications in biological imaging, data storage and organic light-emitting diodes. Bardeen emphasized that the research could have wide-ranging implications.
“The ability to move light energy from one wavelength to another, more useful region, for example, from red to blue, can impact any technology that involves photons as inputs or outputs,” he said.
The research was supported by grants from the National Science Foundation and the US Army.
The research was conducted also by the following coauthors on the research paper: Zhiyuan Huang (first author), Xin Li, Melika Mahboub, Kerry M. Hanson, Valerie M. Nichols and Hoang Le.
Tang’s group helped design the experiments and provided the nanocrystals.
Source:National Institute for Materials Science (NIMS)
Perovskite solar cells are promising low-cost and highly-efficient next-generation solar cells. The ad hoc Team on Perovskite PV Cells (Kenjiro Miyano, Team Leader) at the Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN) (Kohei Uosaki, Director-General), NIMS (Sukekatsu Ushioda, President), successfully developed perovskite solar cells with good reproducibility and stability as well as exhibiting ideal semiconducting properties.
Lead-halide-based perovskite (hereinafter simply referred to as perovskite) has been used as a solar cell material since six years ago. Perovskite solar cells are promising low-cost and highly-efficient next-generation solar cells because they can be produced through low-temperature processes such as spin coating, and generate a large amount of electricity due to their high optical absorption together with the high open-circuit voltage. As such, the research on perovskite solar cells is making rapid progress. In order to identify the semiconducting properties of perovskites and formulate guidelines for the development of highly efficient solar cell materials, NIMS launched an ad hoc Team on Perovskite PV Cells last October led by the deputy director-general of GREEN.
While the conventional perovskite solar cells have demonstrated high conversion efficiency, they were not sufficiently stable plagued by their low reproducibility and the hysteresis in the current-voltage curves depending on the direction of the voltage sweeps. For this reason, the semiconducting properties of perovskites had not been identified. Researchers successfully created reproducible and stable perovskite solar cells as follows;
- They created perovskite solar cells with a simplified structure while strictly eliminating moisture and oxygen by employing the fabrication technique they had developed for the organic solar cells in the past.
- They found that the perovskite solar cells are stable and they observed no hysteresis in the current-voltage curve. Furthermore, they found that the perovskite solar cell material serves as an excellent semiconductor with ideal diode properties.
They proposed an equivalent circuit model that explains the semiconducting properties of perovskites based on analysis of the internal resistance of perovskite solar cells. This model indicated the existence of a charge transport process derived from an impurity level between the conduction and valence bands in the perovskite layer. Due to this transport process, the efficiency of perovskite solar cells may be suppressed to some extent.
In future studies, researchers will investigate into the cause of the impurity level and its influence on solar cells. In addition, they intend to remove the impurity level and improve the efficiency of the solar cells, thereby contributing to energy and environmental conservation.
This study was conducted at GREEN as a part of the MEXT-commissioned project titled “Development of environmental technology using nanotechnology.”
This study had been published in March 2015 in Applied Physics Letters, a journal issued by the American Institute of Physics.
- Kenjiro Miyano, Masatoshi Yanagida, Neeti Tripathi, Yasuhiro Shirai. Simple characterization of electronic processes in perovskite photovoltaic cells. Applied Physics Letters, 2015; 106 (9): 093903 DOI: 10.1063/1.4914086
10 Jun 2015
For many, nuclear fusion is the Holy Grail of energy, offering the possibility of limitless clean energy through harnessing the very same chemical reaction that keeps our Sun burning.
While the potential of fusion is huge, it is a process that requires vast resources and effort, with the International Energy Agency stating that, “extreme temperatures and pressure are needed to initiate and sustain the fusion reaction, making it challenging.”
Fusion is different from the fission power that is used in our nuclear power stations in that energy is generated when atoms are brought together rather than blown apart, which causes radiation.
British Columbia-based General Fusion are hoping that the technology and methods they are developing will herald a new era in nuclear fusion. They have developed what they describe as a “Magnetized Target Fusion system.”
According to the company’s website, the system makes use of a sphere which is filled with molten lead-lithium. This is pumped to create a vortex, into which ‘magnetically confined plasma’ — an electrically charged gas — is injected. Pistons surrounding the sphere are used to drive a wave of pressure into its center, “compressing the plasma to fusion conditions.”
“Fusion is done… [in] two ways,” Michel Laberge, founder and chief scientist of General Fusion, told CNBC’s Sustainable Energy. “Usually… you make a magnetic field and that hold[s] the plasma – which is the hot gas – together, or you have no magnetic field and you crush it very fast with lasers.”
“What we want to do is something in between: we want to make a plasma, a hot gas, with the magnetic field, and then crush the thing with the magnetic field, and because [with] the magnetic field the heat will not escape so fast… that will work a lot better,” Laberge added.
Currently, General Fusion is developing what they describe as ‘full scale subsystems’ that will demonstrate that they can meet performance targets. In the future, they are hoping to build a full scale prototype which they say will be, “designed for single pulse testing, demonstrating full net energy gain on each pulse, a world first.”
“Humanity… needs a source of energy for the future, and we cannot keep on burning fossil fuels,” Laberge said. “Fusion will be powering humanity in the future,” he added.
Did you know that there are experts who evaluate the Energy Department’s work to see if projects really are transforming clean energy economy in sectors like transportation? To gather feedback from the research community, many programs across the Department have annual merit or peer reviews where scientific experts rate projects for their value. This week from June 8 to 12, the Vehicle Technologies Office and Hydrogen and Fuel Cells Program are simultaneously holding their Annual Merit Review and Peer Evaluation Meeting in Washington, D.C., where hundreds of Energy Department-funded projects will be put to the test.
To cover almost all of the work funded by the Vehicle and Fuel Cell Technologies Offices reviewers will judge nearly 400 individual activities. The reviewers come from a variety of backgrounds, including current and former members of the vehicles industry, academia, national laboratories, and government. From back-to-back presentations to poster sessions, the days are intellectually demanding, requiring intense focus and analysis of highly technical projects.
But the valuable feedback will make the challenge worth it. Each reviewer evaluates a set of projects based on how much they contribute to or advance the Energy Department’s missions and goals. The reviewer considers the project’s breadth, depth, appropriateness, accomplishments, and potential. Considering the short and long-term benefits, he or she judges the project based on a standard set of defined metrics. Reviewers provide numeric scores and in-depth comments, creating a comprehensive project report card. After the review, the offices carefully consider the reviewers’ recommendations as they generate work plans, create long-term strategies, and formulate budgets.
Open to the public and free of charge, the Annual Merit Review and Peer Evaluation Meeting provides a great opportunity for those interested in the Energy Department’s research, development, and deployment activities in transportation to learn about the relevant programs. Merit reviews also serve two other valuable purposes: increasing transparency and building a vibrant research community.
Can’t attend? The offices will post the presentations to their websites a few weeks after the meeting. In fact, presentations from past merit reviews are available on the Vehicle Technologies Office website and the Hydrogen and Fuel Cells Program website. About three to four months after the review, the programs also post reports with the results of the review.
Because the reviews bring together breadth and depth of energy experts, they allow researchers in industry, academia, and government to learn about others’ projects. They help scientists see where their work intersects, enabling them to collaborate more effectively. They also facilitate the movement of technology from the government, labs, and universities into the private sector, which can bring them to market.
Merit and peer reviews are invaluable to the government, public and industry. They help keep projects on the right track and drive innovation forward. While the Vehicle Technologies Office and Hydrogen and Fuel Cell 2015 Annual Merit Review and Peer Evaluation meeting is only this week, it will have a positive impact for the clean energy economy of tomorrow. Find out more about the projects being reviewed by following us on Twitter with the hashtags #VTOAMR and #H2AMR.
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Genesis Nanotechnology, Inc. a Canadian and U.S Applied Nanotechnology Company, is identifying and then exploiting for commercialization opportunities, emerging Nanotechnologies that focus on our specific areas of interest:
Water Filtration, Waste-Water Remediation, Renewable Energies (Solar & Fuel Cells), Displays & Super Capacitors (Electronics) and Drug Therapies & Delivery. These ‘disruptive and game changing technologies’, are being researched and developed by experienced research teams at leading Nanotechnology-Development Partnership Universities in Canada, the U.S. and the International University community.
Genesis Nano Technology is actively seeking and evaluating emerging nanotechnology opportunities for Joint Venture Partners and Strategic Alliances that will create ‘enterprise value’ by: identifying, developing, integrating and then commercializing, nanotechnologies that demonstrate significant new disruptive capabilities, enhance new or existing product performance and/or beneficially impact input cost reductions & efficiencies and therefore will achieve a sustainable and competitive advantage in their chosen market sector. “We are the ‘D’ in R & D.”
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Research into organic semiconductors could lead to more efficient LED TVs and flexible solar cells that are cheaper to make and take less energy to produce according to researchers at the University of Bath.
Semiconductors are used in devices such as LED TVs to convert electric current to light; and in photovoltaic cells, which absorb light energy and convert it into electricity. Traditionally ‘inorganic semiconductors’, often based on silicon, are used in such devices. However these are relatively difficult to make and take a lot of energy to produce.
It is estimated that solar cells made from silicon can take a year to pay back the total energy consumed in their manufacture.
Despite efforts over the last three decades to develop organic semiconductors on a mass scale, scientists have been challenged by the fact that this type of semiconductor is less efficient at conducting electricity.
Now, a team from the University of Bath, collaborating with scientists in Germany and The Netherlands, has identified how the electronics industry could overcome some of the existing problems associated with using organic semiconductors.
Semiconductors are used in devices such as LED TVs to convert electric current to light; and in photovoltaic cells, commonly known as solar panels, which absorb light energy and convert it into electricity.
Dr Daniele Di Nuzzo, Research Officer in Physics at the University and first author on the paper, explained: “Conventional semiconductor devices are tricky to make because they first require the production of crystalline materials. Because of this, they also use up a lot of energy to be produced.
“In contrast, organic semiconductors can be processed via printing techniques. For example, organic semiconducting polymers can be dissolved in a solvent to make an electronic ink to be printed onto a surface.
“However they have a disordered structure and conduct electrical charges less well than silicon.”
One way of improving the electrical properties of organic semiconductors is to mix them with ‘doping’ molecules, which work by adding electrical charges to the polymer.
Dr Di Nuzzo added: “It’s difficult currently to implement the doping technique in an effective way to produce organic semiconductor devices that work with high performances. Our research shows why this is the case and suggests how we can improve the performance of these materials.”
The study, published in the journal Nature Communications, found that the size and geometrical position of the doping molecule used had an effect on the efficiency of the semiconductor material.
Dr Enrico Da Como from the University’s Department of Physics, led the study. He explained: “The organic polymer consists of a chain of units which is mixed with the doping molecule before it is printed onto a surface. We found that the doping molecule can bind to the polymer in several different orientations, some of which make a more effective semiconductor than others.
“Our work suggests that if you use a larger doping molecule, you limit the number of ways it can bind to the polymer, making the efficiency of the semiconductor more consistent.”
Explore further: Researchers discover N-type polymer for fast organic battery
More information: Daniele Di Nuzzo, et al “How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers” is published in Nature Communications 6, Article number: 6460 DOI: 10.1038/ncomms7460