Science Current Events | Science News | Brightsurf.com
 

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 Articles


CWRU researchers efficiently charge a lithium-ion battery with solar cell
Consumers aren't embracing electric cars and trucks, partly due to the dearth of charging stations required to keep them moving.

Danish breakthrough brings futuristic electronics a step nearer
When researchers dream about electronics of the future, they more or less dream of pouring liquids into a beaker, stirring them together and decanting a computer out onto the table.

Charge transport in hybrid silicon solar cells
Their results have now been published in the Nature journal Scientific Reports and could point the way toward improvements in hybrid solar cells.

Challenge to classic theory of 'organic' solar cells could improve efficiency
New research findings contradict a fundamental assumption about the functioning of "organic" solar cells made of low-cost plastics, suggesting a new strategy for creating inexpensive solar technology.

Solar cell efficiency could double with novel 'green' antenna
The use of solar energy in the U.S. is growing, but panels on rooftops are still a rare sight. They cost thousands of dollars, and homeowners don't recoup costs for years even in the sunniest or best-subsidized locales.

Reshaping the solar spectrum to turn light to electricity
When it comes to installing solar cells, labor cost and the cost of the land to house them constitute the bulk of the expense.

Spintronics: Molecules stabilizing magnetism
Organic molecules allow producing printable electronics and solar cells with extraordinary properties. In spintronics, too, molecules open up the unexpected possibility of controlling the magnetism of materials and, thus, the spin of the flowing electrons.

Rice University finding could lead to cheap, efficient metal-based solar cells
New research from Rice University could make it easier for engineers to harness the power of light-capturing nanomaterials to boost the efficiency and reduce the costs of photovoltaic solar cells.

An easy, scalable and direct method for synthesizing graphene in silicon microelectronics
In the last decade, graphene has been intensively studied for its unique optical, mechanical, electrical and structural properties.

Sticky tape & phosphorus the key to ultrathin solar cells: ANU media release
Scientists studying thin layers of phosphorus have found surprising properties that could open the door to ultrathin and ultralight solar cells and LEDs.
More Solar Cells Current Events and Solar Cells News Articles

Build Your Own Solar Panel: Generate Electricity from the Sun.

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,
Work...

The Physics of Solar Cells (Properties of Semiconductor Materials)

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...

Practical Photovoltaics: Electricity from Solar Cells, 3rd Edition

Practical Photovoltaics: Electricity from Solar Cells, 3rd Edition
by Richard J. Komp (Author), John Perlin (Foreword)


Practical Photovoltaics, the now-classic reference on solar electricity, offers a unique combination of technical discussion and practical advice. Physicist, lecturer, and solar-home dweller Richard Komp explains the "how" and the "how-to" of PV, while providing valuable information on the industry, new developments, and the future. The book is a comprehensive guide to the theory and reality of solar electricity, as well as a detailed installation and maintenance manual. A well-illustrated appendix offers step-by-step instructions for constructing your own solar module, a creative approach to demystifying the technology. Presented in a clear, concise, and understandable style, Dr. Komp's contribution to PV literature has been called the "best single reference available," "the easiest and...

Solar Electricity Handbook - 2015 Edition: A simple, practical guide to solar energy - designing and installing solar PV systems.

Solar Electricity Handbook - 2015 Edition: A simple, practical guide to solar energy - designing and installing solar PV systems.
by Michael Boxwell (Author)


The Solar Electricity Handbook - 2015 Edition, is a simple, practical guide to using electric solar panels and designing and installing photovoltaic PV systems. Now in its ninth edition, the book assumes no previous knowledge of solar electric systems. The book explains how solar panels work and how they can be used. It explains the advantages of solar energy and the drawbacks that you need to take into account when designing a solar power system. As well as explaining the underlying principles, it provides a step-by-step guide so that you can successfully design and install a photovoltaic solar system from scratch. Unlike many guides, The Solar Electricity Handbook explains the principles behind the technology, allowing the reader to design solar energy systems with confidence. The book...

Physics of Solar Cells: From Basic Principles to Advanced Concepts

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 this...

Build A Solar Hydrogen Fuel Cell System

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...

Organic Solar Cells: Fundamentals, Devices, and Upscaling

Organic Solar Cells: Fundamentals, Devices, and Upscaling
by Barry P. Rand (Editor), Henning Richter (Editor)


Organic photovoltaic (OPV) cells have the potential to make a significant contribution to the increasing energy needs of the future. In this book, 15 chapters written by selected experts explore the required characteristics of components present in an OPV device, such as transparent electrodes, electron- and hole-conducting layers, as well as electron donor and acceptor materials. Design, preparation, and evaluation of these materials targeting highest performance are discussed. This includes contributions on modeling down to the molecular level to device-level electrical and optical testing and modeling, as well as layer morphology control and characterization. The integration of the different components in device architectures suitable for mass production is described. Finally, the...

Solar II: How to Design, Build and Set Up Photovoltaic Components and Solar Electric Systems

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.

Lighting the World: Transforming our Energy Future by Bringing Electricity to Everyone

Lighting the World: Transforming our Energy Future by Bringing Electricity to Everyone
by Jim Rogers (Author)


1.2 billion people on Earth still don't have electricity. Even where cell phones are now common, like sub-Saharan Africa and parts of India, villagers still walk miles to charge them. But new large-scale, sustainable solutions will not only usher in a new era of light, but be an important first step in lifting people from poverty and putting them on a road of sustainable economic development. Also, a unique, transforming opportunity for Western thinkers and practitioners will be created. These areas have largely skipped the analog stage of power development, and have moved straight from the middle ages to the digital age. They are not encumbered by existing infrastructure, dependence on fossil fuels, or too many outdated laws and regulations. An ideal innovation incubator, the developing...

Solar Cell Device Physics, Second Edition

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...

© 2015 BrightSurf.com