Third generation solar cell
Encyclopedia
Third generation solar cells are solar cell
s that are potentially able to overcome the Shockley–Queisser limit of 31-41% power efficiency for single bandgap solar cells. This includes a range of alternatives to the so-called "first generation solar cells" (which are solar cells made of semiconducting p-n junction
s) and "second generation solar cells" (based on reducing the cost of first generation cells by employing thin film
technologies). Common third-generation systems include multi-layer ("tandem") cells made of amorphous silicon
or gallium arsenide, while more theoretical developments include frequency conversion
, hot-carrier effects and other multiple-carrier ejection.
s in the antenna material, an electronic valve that traps the electrons as they pop off the end of the antenna, and a tuner that amplifies electrons of a selected frequency. It is possible to build a solar cell identical to a radio, a system known as an optical rectenna, but to date these have not been practical.
Instead, the vast majority of the solar electric market is made up of silicon-based devices. In silicon cells, the silicon acts as both the antenna (or electron donor
, technically) as well as the electronic valve. Silicon is almost ideal as a solar cell material; it is widely available, relatively inexpensive, and has a bandgap that is ideal for solar collection. On the downside it is energetically expensive to produce silicon in bulk, and great efforts have been made to reduce or eliminate the silicon in a cell. Moreover it is mechanically fragile, which typically requires a sheet of strong glass to be used as mechanical support and protection from the elements. The glass alone is a significant portion of the cost of a typical solar module.
According to the Shockley–Queisser limit, the majority of a cell's theoretical efficiency is due to the difference in energy between the bandgap and solar photon. Any photon with more energy than the bandgap can cause photoexcitation, but in this case any energy above and beyond the bandgap energy is lost. Consider the solar spectrum; only a small portion of the light reaching the ground is blue, but those photons have three times the energy of red light. Silicon's bandgap is 1.1 eV, about that of red light, so in this case the extra energy contained in blue light is lost in a silicon cell. If the bandgap is tuned higher, say to blue, that energy is now captured, but only at the cost of rejecting all the lower energy photons.
It is possible to greatly improve on a single-junction cell by stacking extremely thin cells with different bandgaps on top of each other - the "tandem cell" or "multi-junction"
approach. Traditional silicon preparation methods do not lend themselves to this approach. There has been some progress using thin-films of amorphous silicon, notably Uni-Solar's products, but other issues have prevented these from matching the performance of traditional cells. Most tandem-cell structures are based on higher performance semiconductors, notably gallium arsenide (GaAs). Three-layer GaAs cells hold the production record of 41.6% for experimental examples.
Numerical analysis shows that the "perfect" single-layer solar cell should have a bandgap of 1.13 eV, almost exactly that of silicon. Such a cell can have a maximum theoretical power conversion efficiency of 33.7% - the solar power below red (in the infrared) is lost, and the extra energy of the higher colors is also lost. For a two layer cell, one layer should be tuned to 1.64 eV and the other at 0.94 eV, with a theoretical performance of 44%. A three-layer cell should be tuned to 1.83, 1.16 and 0.71 eV, with an efficiency of 48%. A theoretical "infinity-layer" cell would have a theoretical efficiency of 64%.
technologies (including polymer cells and biomimetics
), quantum dot
, tandem/multi-junction cells, intermediate band solar cell , hot-carrier cells, upconversion and downconversion technologies, and solar thermal technologies, such as thermophotonics
, which is one technology identified by Green as being third generation.
It also includes:
, have invested hundreds of millions of dollars towards this new generation of solar power. They are counting on the likely possibility that the new technologies could compete with not only traditional solar cells, but more importantly with fossil fuels and nuclear energy (to reach and surpass grid parity
). This would revolutionize our energy market
; as said, in order for this to happen, third generation solar cells will need to be more efficient and cheaper.
and lightweight physical characteristics of the different types of third generation solar cells makes many new applications possible.
There is the possibility that solar cells could be integrated into clothing which would allow us to have personal wireless power without batteries.
Another plausible application could be a type of automobile paint that is blended with polymer solar cells. This could help maintain the lightweight form of a solar car
while still providing ample energy to power it.
One application of third generation solar cells that has the possibility of becoming commercially viable relatively soon is solar paint. Tata Steel is working with researchers at Swansea University to produce sheet steel treated with a sensitive coating of solar cells. According to Dr. Worsley, the project leader for the Swansea Solar Paint Project, if all the steel cladding produced by one manufacturer was energy generating, it would be the equivalent of 50 wind farms (or 4500 gigawatts/year) at an efficiency rate of 5%.
A-Si
CdTe (second generation)
CIGS
(copper indium gallium selenide) (second generation)
Nanocrystal solar cell
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s that are potentially able to overcome the Shockley–Queisser limit of 31-41% power efficiency for single bandgap solar cells. This includes a range of alternatives to the so-called "first generation solar cells" (which are solar cells made of semiconducting p-n junction
P-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
s) and "second generation solar cells" (based on reducing the cost of first generation cells by employing thin film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
technologies). Common third-generation systems include multi-layer ("tandem") cells made of amorphous silicon
Amorphous silicon
Amorphous silicon is the non-crystalline allotropic form of silicon. It can be deposited in thin films at low temperatures onto a variety of substrates, offering some unique capabilities for a variety of electronics.-Description:...
or gallium arsenide, while more theoretical developments include frequency conversion
Frequency conversion
Frequency conversion may refer to different processes affecting frequency of physical phenomena:* A frequency changer is an electronic device that converts alternating current of one frequency to alternating current of another frequency....
, hot-carrier effects and other multiple-carrier ejection.
Background
Solar cells can be thought of as visible light counterparts to radio receivers. A receiver consists of three basic parts; an antenna that converts the radio waves (light) into wave-like motions of electronElectron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s in the antenna material, an electronic valve that traps the electrons as they pop off the end of the antenna, and a tuner that amplifies electrons of a selected frequency. It is possible to build a solar cell identical to a radio, a system known as an optical rectenna, but to date these have not been practical.
Instead, the vast majority of the solar electric market is made up of silicon-based devices. In silicon cells, the silicon acts as both the antenna (or electron donor
Electron donor
An electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process....
, technically) as well as the electronic valve. Silicon is almost ideal as a solar cell material; it is widely available, relatively inexpensive, and has a bandgap that is ideal for solar collection. On the downside it is energetically expensive to produce silicon in bulk, and great efforts have been made to reduce or eliminate the silicon in a cell. Moreover it is mechanically fragile, which typically requires a sheet of strong glass to be used as mechanical support and protection from the elements. The glass alone is a significant portion of the cost of a typical solar module.
According to the Shockley–Queisser limit, the majority of a cell's theoretical efficiency is due to the difference in energy between the bandgap and solar photon. Any photon with more energy than the bandgap can cause photoexcitation, but in this case any energy above and beyond the bandgap energy is lost. Consider the solar spectrum; only a small portion of the light reaching the ground is blue, but those photons have three times the energy of red light. Silicon's bandgap is 1.1 eV, about that of red light, so in this case the extra energy contained in blue light is lost in a silicon cell. If the bandgap is tuned higher, say to blue, that energy is now captured, but only at the cost of rejecting all the lower energy photons.
It is possible to greatly improve on a single-junction cell by stacking extremely thin cells with different bandgaps on top of each other - the "tandem cell" or "multi-junction"
Multijunction photovoltaic cell
Multi-junction solar cells or tandem cells are solar cells containing several p-n junctions. Each junction is tuned to a different wavelength of light, reducing one of the largest inherent sources of losses, and thereby increasing efficiency...
approach. Traditional silicon preparation methods do not lend themselves to this approach. There has been some progress using thin-films of amorphous silicon, notably Uni-Solar's products, but other issues have prevented these from matching the performance of traditional cells. Most tandem-cell structures are based on higher performance semiconductors, notably gallium arsenide (GaAs). Three-layer GaAs cells hold the production record of 41.6% for experimental examples.
Numerical analysis shows that the "perfect" single-layer solar cell should have a bandgap of 1.13 eV, almost exactly that of silicon. Such a cell can have a maximum theoretical power conversion efficiency of 33.7% - the solar power below red (in the infrared) is lost, and the extra energy of the higher colors is also lost. For a two layer cell, one layer should be tuned to 1.64 eV and the other at 0.94 eV, with a theoretical performance of 44%. A three-layer cell should be tuned to 1.83, 1.16 and 0.71 eV, with an efficiency of 48%. A theoretical "infinity-layer" cell would have a theoretical efficiency of 64%.
Technologies
The third generation is somewhat ambiguous in the technologies that it encompasses, though generally it tends to include, among others, non-semiconductorSemiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
technologies (including polymer cells and biomimetics
Biomimetics
Biomimetics is the study of the structure and function of biological systems as models for the design and engineering of materials and machines. It is widely regarded as being synonymous with biomimicry, biomimesis, biognosis and similar to biologically inspired design.-History:The term biomimetics...
), quantum dot
Quantum dot
A quantum dot is a portion of matter whose excitons are confined in all three spatial dimensions. Consequently, such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. They were discovered at the beginning of the 1980s by Alexei...
, tandem/multi-junction cells, intermediate band solar cell , hot-carrier cells, upconversion and downconversion technologies, and solar thermal technologies, such as thermophotonics
Thermophotonics
Thermophotonics is a concept for generating usable power from heat which shares some features of thermophotovoltaic power generation. A TPX system consists of a light-emitting diode , a photovoltaic cell, an optical coupling between the two, and an electronic control circuit...
, which is one technology identified by Green as being third generation.
It also includes:
- Silicon nanostructures
- Modifying incident spectrum (concentration), to reach 300-500 suns and efficiencies of 32% (already attained in Sol3g cells ) to +50%.
- Use of excess thermal generation (caused by UV light) to enhance voltages or carrier collection.
- Use of infraredInfraredInfrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
spectrum to produce electricity at night.
Expected market shift
There has been a lot of hype circling around the possibilities of advanced solar technology in recent years. Major companies and investors such as GoogleGoogle
Google Inc. is an American multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its AdWords program...
, have invested hundreds of millions of dollars towards this new generation of solar power. They are counting on the likely possibility that the new technologies could compete with not only traditional solar cells, but more importantly with fossil fuels and nuclear energy (to reach and surpass grid parity
Grid parity
Grid parity is the point at which alternative means of generating electricity is at least as cheap as grid power.For solar energy, it is achieved first in areas with abundant sun and high costs for electricity such as in California, Hawaii, Spain and Japan. Many solar power advocates predict that...
). This would revolutionize our energy market
Energy market
Energy markets are those commodities markets that deal specifically with the trade and supply of energy. Energy market may refer to an electricity market, but can also refer to other sources of energy...
; as said, in order for this to happen, third generation solar cells will need to be more efficient and cheaper.
Future possibilities
The new materials that solar energy can be harnessed with is one of the most exciting elements of the new technology. The flexibleFlexible electronics
Flexible electronics, also known as flex circuits, is a technology for assembling electronic circuits by mounting electronic devices on flexible plastic substrates, such as polyimide, PEEK or transparent conductive polyester film. Additionally, flex circuits can be screen printed silver circuits on...
and lightweight physical characteristics of the different types of third generation solar cells makes many new applications possible.
There is the possibility that solar cells could be integrated into clothing which would allow us to have personal wireless power without batteries.
Another plausible application could be a type of automobile paint that is blended with polymer solar cells. This could help maintain the lightweight form of a solar car
Solar car
A solar vehicle is an electric vehicle powered completely or significantly by direct solar energy. Usually, photovoltaic cells contained in solar panels convert the sun's energy directly into electric energy. The term "solar vehicle" usually implies that solar energy is used to power all or part...
while still providing ample energy to power it.
One application of third generation solar cells that has the possibility of becoming commercially viable relatively soon is solar paint. Tata Steel is working with researchers at Swansea University to produce sheet steel treated with a sensitive coating of solar cells. According to Dr. Worsley, the project leader for the Swansea Solar Paint Project, if all the steel cladding produced by one manufacturer was energy generating, it would be the equivalent of 50 wind farms (or 4500 gigawatts/year) at an efficiency rate of 5%.
Types of third generation solar cells
While the new solar technologies that have been discovered center around nanotechnology, there are several different material methods currently used.A-Si
- Anwell Technologies LimitedAnwell Technologies LimitedAnwell Technologies Limited is a supplier of manufacturing equipment with trading and manufacturing business in optical disc and solar cell. They vertically integrated into manufacturing business of optical disc and solar cell in 2007 and 2008...
- Uni-Solar
CdTe (second generation)
- First SolarFirst SolarFirst Solar, Inc. is an American manufacturer of thin film photovoltaic modules, or solar panels, and a provider to PV power plants of supporting services that include finance, construction, maintenance and end-of-life panel recycling...
CIGS
Copper indium gallium selenide
Copper indium gallium selenide is a I-III-VI2 semiconductor material composed of copper, indium, gallium, and selenium. The material is a solid solution of copper indium selenide and copper gallium selenide...
(copper indium gallium selenide) (second generation)
- HondaHondais a Japanese public multinational corporation primarily known as a manufacturer of automobiles and motorcycles.Honda has been the world's largest motorcycle manufacturer since 1959, as well as the world's largest manufacturer of internal combustion engines measured by volume, producing more than...
Solar - NanosolarNanosolarNanosolar is a developer of solar power technology. Based in San Jose, CA, Nanosolar has developed and commercialized a low-cost printable solar cell manufacturing process. The company started selling panels mid-December 2007, and plans to sell them at around $1 per watt...
- Solarion
- SolyndraSolyndraSolyndra was a manufacturer of cylindrical panels of CIGS thin-film solar cells based in Fremont, California. Although the company was once touted for its unusual technology, plummeting silicon prices led to the company being unable to compete with more conventional solar panels...
Nanocrystal solar cell
Nanocrystal solar cell
Quantum dot solar cells are an emerging field in solar cell research that uses quantum dots as the photovoltaic material, as opposed to better-known bulk materials such as silicon, copper indium gallium selenide or CdTe. Quantum dots have bandgaps that are tunable across a wide range of energy...
- Innovalight http://www.innovalight.com/index.html
See also
- Band gapBand gapIn solid state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference between the top of the valence band and the...
- Grid parityGrid parityGrid parity is the point at which alternative means of generating electricity is at least as cheap as grid power.For solar energy, it is achieved first in areas with abundant sun and high costs for electricity such as in California, Hawaii, Spain and Japan. Many solar power advocates predict that...
- HCPV
- Low-cost solar cell
- Nanoantenna
- Organic electronicsOrganic electronicsOrganic electronics, plastic electronics or polymer electronics, is a branch of electronics dealing with conductive polymers, plastics, or small molecules. It is called 'organic' electronics because the polymers and small molecules are carbon-based...
- PhotovoltaicsPhotovoltaicsPhotovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...
- Printed electronicsPrinted electronicsPrinted electronics is a set of printing methods used to create electrical devices on various substrates. Printing typically uses common printing equipment or other low-cost equipment suitable for defining patterns on material, such as screen printing, flexography, gravure, offset lithography and...
- Solar CellSolar cellA solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
External links
- http://light.utoronto.ca/tsargent/biography.html
- Different generations of solar cells
- Research in Virginia Tech.
- Solar Shootout in the San Joaquin Valley.