The solar cell that also shines: Luminescent 'LED-type' design breaks efficiency record
April 20, 2012
To produce the maximum amount of energy, solar cells are designed to absorb as much light from the Sun as possible. Now researchers from the University of California, Berkeley, have suggested - and demonstrated - a counterintuitive concept: solar cells should be designed to be more like LEDs, able to emit light as well as absorb it. The Berkeley team will present its findings at the Conference on Lasers and Electro Optics (CLEO: 2012), to be held May 6-11 in San Jose, Calif.
"What we demonstrated is that the better a solar cell is at emitting photons, the higher its voltage and the greater the efficiency it can produce," says Eli Yablonovitch, principal researcher and UC Berkeley professor of electrical engineering.
Since 1961, scientists have known that, under ideal conditions, there is a limit to the amount of electrical energy that can be harvested from sunlight hitting a typical solar cell. This absolute limit is, theoretically, about 33.5 percent. That means that at most 33.5 percent of the energy from incoming photons will be absorbed and converted into useful electrical energy.
Yet for five decades, researchers were unable to come close to achieving this efficiency: as of 2010, the highest anyone had come was just more than 26 percent. (This is for flat-plate, "single junction" solar cells, which absorb light waves above a specific frequency. "Multi-junction" cells, which have multiple layers and absorb multiple frequencies, are able to achieve higher efficiencies.)
More recently, Yablonovitch and his colleagues were trying to understand why there has been such a large gap between the theoretical limit and the limit that researchers have been able to achieve. As they worked, a "coherent picture emerged," says Owen Miller, a graduate student at UC Berkeley and a member of Yablonovitch's group. They came across a relatively simple, if perhaps counterintuitive, solution based on a mathematical connection between absorption and emission of light.
"Fundamentally, it's because there's a thermodynamic link between absorption and emission," Miller says. Designing solar cells to emit light - so that photons do not become "lost" within a cell - has the natural effect of increasing the voltage produced by the solar cell. "If you have a solar cell that is a good emitter of light, it also makes it produce a higher voltage," which in turn increases the amount of electrical energy that can be harvested from the cell for each unit of sunlight, Miller says.
The theory that luminescent emission and voltage go hand in hand is not new. But the idea had never been considered for the design of solar cells before now, Miller continues.
This past year, a Bay area-based company called Alta Devices, co-founded by Yablonovitch, used the new concept to create a prototype solar cell made of gallium arsenide (GaAs), a material often used to make solar cells in satellites. The prototype broke the record, jumping from 26 percent to 28.3 percent efficiency. The company achieved this milestone, in part, by designing the cell to allow light to escape as easily as possible from the cell - using techniques that include, for example, increasing the reflectivity of the rear mirror, which sends incoming photons back out through the front of the device.
Solar cells produce electricity when photons from the Sun hit the semiconductor material within a cell. The energy from the photons knocks electrons loose from this material, allowing the electrons to flow freely. But the process of knocking electrons free can also generate new photons, in a process called luminescence. The idea behind the novel solar cell design is that these new photons - which do not come directly from the Sun - should be allowed to escape from the cell as easily as possible.
"The first reaction is usually, why does it help [to let these photons escape]?" Miller says. "Don't you want to keep [the photons] in, where maybe they could create more electrons?" However, mathematically, allowing the new photons to escape increases the voltage that the cell is able to produce.
The work is "a good, useful way" of determining how scientists can improve the performance of solar cells, as well as of finding creative new ways to test and study solar cells, says Leo Schowalter of Crystal IS, Inc. and visiting professor at Rensselaer Polytechnic Institute, who is chairman of the CLEO committee on LEDs, photovoltaics, and energy-efficient photonics.
Yablonovitch says he hopes researchers will be able to use this technique to achieve efficiencies close to 30 percent in the coming years. And since the work applies to all types of solar cells, the findings have implications throughout the field.
Optical Society of America
Related Solar Cells Current Events and Solar Cells News ArticlesFirst-ever look inside a working lithium-ion battery
For the first time, researchers have been able to open a kind of window into the inner workings of a lithium-ion battery.Phosphorus a promising semiconductor
Defects damage the ideal properties of many two-dimensional materials, like carbon-based graphene. Phosphorus just shrugs.Rethinking the basic science of graphene synthesis
A new route to making graphene has been discovered that could make the 21st century's wonder material easier to ramp up to industrial scale.Breakthrough for Carbon Nanotube Solar Cells
Lighter, more flexible, and cheaper than conventional solar-cell materials, carbon nanotubes (CNTs) have long shown promise for photovoltaics. But research stalled when CNTs proved to be inefficient, converting far less sunlight into power than other methods.Future solar panels
Conventional photovoltaic technology uses large, heavy, opaque, dark silicon panels, but this could soon change.Recycling old batteries into solar cells
This could be a classic win-win solution: A system proposed by researchers at MIT recycles materials from discarded car batteries - a potential source of lead pollution - into new, long-lasting solar panels that provide emissions-free power.Notre Dame paper offers insights into a new class of semiconducting materials
A new paper by University of Notre Dame researchers describes their investigations of the fundamental optical properties of a new class of semiconducting materials known as organic-inorganic "hybrid" perovskites. Eco-friendly 'pre-fab nanoparticles' could revolutionize nano manufacturing
A team of materials chemists, polymer scientists, device physicists and others at the University of Massachusetts Amherst today report a breakthrough technique for controlling molecular assembly of nanoparticles over multiple length scales that should allow faster, cheaper, more ecologically friendly manufacture of organic photovoltaics and other electronic devices.Could hemp nanosheets topple graphene for making the ideal supercapacitor?
As hemp makes a comeback in the U.S. after a decades-long ban on its cultivation, scientists are reporting that fibers from the plant can pack as much energy and power as graphene, long-touted as the model material for supercapacitors. Self-cooling solar cells boost power, last longer
Scientists may have overcome one of the major hurdles in developing high-efficiency, long-lasting solar cells-keeping them cool, even in the blistering heat of the noonday Sun.
More Solar Cells Current Events and Solar Cells News Articles
Build Your Own Solar Panel: Generate Electricity from the Sun.|
by Phillip Hurley (Author)
Whether you're trying to get off the grid, or you just like to experiment, Build Your Own Solar Panel has all the information you need to build your own photovoltaic panel to generate electricity from the sun. Now available for the first time in print, this revised and expanded edition has easy-to-follow directions, and over 150 detailed photos and illustrations. Lists of materials, tools, and suppliers of PV cells are included. Every-day tools are all that you need to complete these projects.
Build Your Own Solar Panel will show you how to:
Design and build PV panels,
Customize panel output,
Make tab and bus ribbon,
Solder cell connections,
Wire a photovoltaic panel,
Purchase solar cells,
Test and rate PV cells,
Repair damaged solar cells,
Solar Cell Device Physics, Second Edition|
by Stephen Fonash (Author)
There has been an enormous infusion of new ideas in the field of solar cells over the last 15 years; discourse on energy transfer has gotten much richer, and nanostructures and nanomaterials have revolutionized the possibilities for new technological developments. However, solar energy cannot become ubiquitous in the world's power markets unless it can become economically competitive with legacy generation methods such as fossil fuels.
The new edition of Dr. Stephen Fonash's definitive text points the way toward greater efficiency and cheaper production by adding coverage of cutting-edge topics in plasmonics, multi-exiton generation processes, nanostructures and nanomaterials such as quantum dots. The book's new structure improves readability by shifting many detailed equations to...
The Physics of Solar Cells (Properties of Semiconductor Materials)|
by Jenny Nelson (Author)
This book provides a comprehensive introduction to the physics of the photovoltaic cell. It is suitable for undergraduates, graduate students, and researchers new to the field. It covers: basic physics of semiconductors in photovoltaic devices; physical models of solar cell operation; characteristics and design of common types of solar cell; and approaches to increasing solar cell efficiency. The text explains the terms and concepts of solar cell device physics and shows the reader how to formulate and solve relevant physical problems. Exercises and worked solutions are included. Contents: Photons In, Electrons Out: Basic Principles of PV; Electrons and Holes in Semiconductors; Generation and Recombination; Junctions; Analysis of the p n Junction; Monocrystalline Solar Cells; Thin Film...
Physics of Solar Cells: From Basic Principles to Advanced Concepts|
by Peter Würfel (Author)
Based on the highly regarded and extremely successful first edition, this thoroughly revised, updated and expanded edition contains the latest knowledge on the mechanisms of solar energy conversion.
The textbook describes in detail all aspects of solar cell function, the physics behind every single step, as well as all the issues to be considered when improving solar cells and their efficiency.
Requiring no more than standard physics knowledge, the book enables both students and researchers to understand the factors driving conversion efficiency and to apply this knowledge to their own solar cell development.
New exercises after each chapter help students to consolidate their freshly acquired knowledge, while the book also serves as a reference for researchers already working in...
Solar Electricity Handbook - 2014 Edition: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems|
by Mr Michael Boxwell (Author)
Solar electricity is a wonderful concept. Take free power from the sun and use it to power electrical equipment. No ongoing electricity bills, no reliance on an electricity socket. 'Free' electricity that does not harm the planet. Of course, it is not as simple as that. Yet generating electricity from sunlight alone is a powerful resource with applications and benefits throughout the world. But how does it work? What is it suitable for? How much does it cost? How do I install it? This best selling internet-linked book answers all these questions and shows you how to use the power of the sun to generate electricity yourself. This sixth edition includes more information, with new and improved chapters for grid-tie systems and brings the book right up to date with the latest technology and...
Solar Cells, Second Edition: Materials, Manufacture and Operation|
by Augustin McEvoy (Author), L. Castaner (Author), Tom Markvart (Author)
Enormous leaps forward in the efficiency and the economy of solar cells are being made at a furious pace. New materials and manufacturing processes have opened up new realms of possibility for the application of solar cells. Crystalline silicon cells are increasingly making way for thin film cells, which are spawning experimentation with third-generation high-efficiency multijunction cells, carbon-nanotube based cells, UV light for voltage enhancement, and the use of the infrared spectrum for night-time operation, to name only a few recent advances. This thoroughly updated new edition of Markvart and Castaner's Solar Cells, extracted from their industry standard Practical Handbook of Photovoltaics, is the definitive reference covering the science and operation, materials and manufacture...
Solar Cell & Energy Guide|
by Silicon Solar
Solar Cell Book
The solar cell book is an information packet on the basics of solar energy. The topics that are covered in the solar cell book are vast but brief. There is just enough information to help you understand how solar cells and solar power work in order to fully understand how everything works you’d need a lot bigger book. There is also information on interconnecting solar cells along with various diagrams that help you understand the ins and outs of solar cells. There is also a class project section with various degrees of difficulty that range from elementary to intermediate levels.
Peak Watt (Wp)
Diamond Solar Cells
Interconnecting Solar Cells
Build A Solar Hydrogen Fuel Cell System|
by Phillip Hurley (Author)
Learn how to construct and operate the components of a solar hydrogen fuel cell system: the fuel cell stack, the electrolyzer to generate hydrogen fuel, simple hydrogen storage, and solar panels designed specifically to run electrolyzers for hydrogen production. Complete, clear, illustrated instructions to build all the major components make it easy for the non-engineer to understand and work with this important new technology. Featured are the author's innovative and practical designs for efficient solar powered hydrogen production including: ESPMs (Electrolyzer Specific Photovoltaic Modules) – 40 watt solar panels designed specifically to run electrolyzers efficiently; a 40-80 watt electrolyzer for intermittant power from renewable energy sources such as solar and wind; and, a 6-12...
Solar II: How to Design, Build and Set Up Photovoltaic Components and Solar Electric Systems|
by Phillip Hurley (Author)
Now that you've built your solar panels, how do you set up a photovoltaic system and plug in? In Solar II, Phillip Hurley, author of Build Your Own Solar Panel, will show you how to:
Calculate daily electrical usage and needs
Plan and size your solar electric system
Build racks and charge controllers
Mount and orient PV panels
Wire solar panel arrays
Make a ventilated battery box
Wire battery arrays for solar panels
Install an inverter
Maintain solar batteries for optimum life and performance
Make your own combiner box, bus bars, and DC and AC service boxes
Solar II includes easy-to-follow directions with over 150 black & white photos, illustrations and schematics.
Solar Electricity Handbook - 2013 Edition: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems|
by Mr Michael Boxwell (Author)
The 2013 edition of the Solar Electricity Handbook is a practical and straightforward guide to using photovoltaic solar panels to generate electricity. It is the seventh edition of the book, which has been updated yearly since 2009.
Assuming no previous knowledge of solar panels, the book explains how solar panels work, how they can be used and explains the steps you need to take to successfully design and install a solar electric system from scratch using photovoltaic solar panels.Accompanying this book is a solar resource website containing lots of useful information, lists of suppliers and on-line solar energy calculators that will simplify the cost analysis and design processes.
Why buy the Solar Electricity Handbook?
The Handbook is a simple, practical guide to using...