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


Caltech scientists develop cool process to make better graphene
A new technique invented at Caltech to produce graphene--a material made up of an atom-thick layer of carbon--at room temperature could help pave the way for commercially feasible graphene-based solar cells and light-emitting diodes, large-panel displays, and flexible electronics.

Scientists move closer to '2 for 1 deal' on solar cell efficiency
The underlying mechanism behind an enigmatic process called "singlet exciton fission", which could enable the development of significantly more powerful solar cells, has been identified by scientists in a new study.

A new method for making perovskite solar cells
Research led by a Brown University Ph.D. student has revealed a new way to make light-absorbing perovskite films for use in solar cells.

Uncovering the secrets of super solar power perovskites
The best hope for cheap, super-efficient solar power is a remarkable family of crystalline materials called hybrid perovskites.

Molecule-making machine simplifies complex chemistry
A new molecule-making machine could do for chemistry what 3-D printing did for engineering: Make it fast, flexible and accessible to anyone.

3-D printer for small molecules opens access to customized chemistry
Howard Hughes Medical Institute scientists have simplified the chemical synthesis of small molecules, eliminating a major bottleneck that limits the exploration of a class of compounds offering tremendous potential for medicine and technology.

Researchers develop new approach that combines biomass conversion, solar energy conversion
In a study published March 9 in Nature Chemistry, University of Wisconsin-Madison chemistry Professor Kyoung-Shin Choi presents a new approach to combine solar energy conversion and biomass conversion, two important research areas for renewable energy.

Solar cells get growth boost
Researchers at the Okinawa Institute of Science and Technology Graduate University's (OIST) Energy Materials and Surface Sciences Unit have found that growing a type of film used to manufacture solar cells in ambient air gives it a growth boost.

UC research partnership explores how to best harness solar power
A University of Cincinnati research partnership is reporting advances on how to one day make solar cells stronger, lighter, more flexible and less expensive when compared with the current silicon or germanium technology on the market.

International research partnership tricks the light fantastic
What if one day, your computer, TV or smart phone could process data with light waves instead of an electrical current, making those devices faster, cheaper and more sustainable through less heat and power consumption?
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...

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...

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...

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...

Solar Electricity Handbook - 2013 Edition: A Simple Practical Guide to Solar Energy - Designing and Installing Photovoltaic Solar Electric Systems

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...

Solar Cells, Second Edition: Materials, Manufacture and Operation

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 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.

Materials Concepts for Solar Cells (Energy Futures)

Materials Concepts for Solar Cells (Energy Futures)
by Thomas Dittrich (Author)


This textbook bridges the gap between basic literature on the physics of solar cells and highly specialized books about photovoltaic solar energy conversion. It is intended to give students with a background in engineering, materials science, chemistry or physics a comprehensive introduction to materials concepts for solar cells. To this end, general principles of solar cells and materials demands are explained in the first part of this book. The second part is devoted to the four classes of materials concepts for solar cells: solar cells based on crystals of silicon, epitaxial layer systems of III-V semiconductors, thin-film absorbers on foreign substrates, and nano-composite absorbers.Readership: Advanced undergraduates and graduate students in photovoltaics.

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...

Solar Cell Radiation Handbook: Third Edition

Solar Cell Radiation Handbook: Third Edition
by National Aeronautics and Space Administration (Author)


This handbook is intended to furnish the reader with the necessary tools to permit him to predict the degradation of solar cell electrical performance in any given space radiation environment. It begins with an introduction to solar cell theory, describing how cells are manufactured and how they are modeled mathematically. The interaction of energetic charged particle radiation with solar cells is discussed in detail and the concept of 1 MeV equivalent electron fluence is introduced. The space radiation environment is described and methods of calculating equivalent fluences for the space environment are developed. A computer program was written to perform the equivalent fluence calculations and a Fortran listing of the program is included. Finally, an extensive body of data detailing the...

© 2015 BrightSurf.com