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Although solar energy is a very small component of the overall sources of energy, the use of solar energy is growing significantly. But an exponential increase of the production capacity of the solar energy is still needed in order to satisfy the needs of energy.
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===Utilization of Solar Energy===
</table>
[[category:organic solar cell]]


A 42% annual growth rate of cumulative installed capacity has been fairly steady in recent years and been accompanied by a steady decrease of the price of solar modules (per watt), from nearly $100 in 1976 down to an average of $4. That trend is often referred to as the learning curve.
In year 2005, for the first time in history a total of over 1 GW of power capacity was added, increasing the cumulative installed capacity by 42% reaching a value of 3.7 GW in the IEA PVPS countries (90% of the worldwide production). The greatest proportion was installed by Germany and Japan alone (85%).


Solar energy can be used even for a household. Solar cells may be on the top of the roof and solar energy can be collected for use in a household. BOS (balance of system) cost is larger for off-grid applications because they require a storage device. That solar energy could also be distributed back into the electrical grid when there is an overproduction with respect to your own needs. This distributed system is useful because every house can collect the energy not only for themselves but they can also transfer the source back on the electrical grid. You can also centralize power stations that would be grid connected and would work as normal electrical power stations.
Although solar energy is a very small component of the overall sources of energy, its use is growing significantly. An exponential increase in the production capacity of solar energy is still needed in order to satisfy the energy needs of today.


===Generations of Solar Cells===
[[Image:Direct_normal_solar_radiation_2004.jpg|thumb|300px|This map shows the average irradiance of the US.<ref>http://www.nrel.gov/gis/solar.html</ref>]]
*First Generation Solar Cells
 
The solar cells that you have on the market are made out of crystalline silicon, multcrystalline ribbon, or ingot, are also known as the "first generation solar cells". Right now the majority of the modules of the cells come from crystalline silicon. The supply of silicon is starting to tighten. Other elements such as indium that is the most common transparent conductor in the form of ITO is also increasing in demand. Amorphous silicon is also being used but less efficient. Then you have thin films like amorphous silicon which is much less costly in terms of its application. The power conversion efficiency for silicon is about 20%. (Pmax/Psun) Because they are made from crystalline silicon they are structurally rigid which makes them hared to process and distribute.
==Utilization of Solar Energy==
[[Image:Pv_worldwide.png|thumb|400px|The U.S. lags other countries in PV shipments.<ref>http://www.nrel.gov/analysis/pdfs/46025.pdf</ref>]]
A 42% annual growth rate of cumulative installed PV capacity has been fairly steady in recent years and been accompanied by a steady decrease in the price of solar modules (per watt), from nearly $100 in 1976 down to an average of $4. In 2005, for the first time in history, a total of over 1 Gigawatt (GW) of power capacity was added, increasing the cumulative installed capacity to a value of 3.7 GW in established industrial countries. The greatest proportion (85%) was provided by Germany and Japan alone.
 
"Generation I" (single crystal and poly-crystal silicon) solar cells may be found on roof tops, and in large power generating arrays around the world.   The balance of system (BOS) cost is generally larger for off-grid applications because they require a storage device, such as an array of lead-acid batteries.  For on-grid houses or industries, solar-generated electricity can be distributed back into the electrical grid when production exceeds the needs of the user.
 
Organic solar cells (organic photovoltaics or OPVs) are an emerging Generation III technology, providing another lightweight option for off-grid applications (e.g. chargers for portable electronics). OPVs may eventually compete for power generation with Generation I on-grid devices if their efficiencies and lifetimes are high enough, and their costs low enough.
 
==Generations of Solar Cells==
[[Image:Cost-efficiency pv.jpg|center|thumb|500px|Graph of efficiency vs. cost for generations of solar cells. Courtesy of Martin Green]]
<br clear='all'>
=== First Generation ===
[[Image:Solar_panels_on_house_roof.jpg|thumb|300px|Silicon solar panels on a roof]]
 
Solar cells currently on the market are almost all Generation I devices made from crystalline silicon, considered to be a "mature" technology.  They are somewhat expensive to produce because of the high processing costs needed to create silicon cells with sufficient purity and long range-order. See [[Types of Solar Cells]]
 
=== Second Generation ===
 
Generation II materials are less mature as a PV technology, and are generally created using vacuum deposition or chemical vapor deposition (CVD). These include CdTe or copper-indium-gallium-selenide (CIGS) technologies.  Their costs are lower, as are their efficiencies, but they are thinner and lighter than silicon cells.  Disposal at end-of-life is a consideration, because of the toxicity of Cd, Te, Ga, and Se, and because of concerns regarding their earth abundance.


See DOE report on solar energy research<ref>http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf</ref>
See DOE report on solar energy research<ref>http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf</ref>


*Second Generation Solar Cells
=== Third Generation ===
Other films like CIGS which is copper indium gallium selenide or cadmium teluride or III-V for instance gallium indium are the group three elements. Those thin films are referred to as the 2nd generation solar cells.
 
OPVs come in several different platforms, and when fully optimized, will be light-weight, low-cost, flexible and easily scalable energy conversion platforms.  Their mode of energy conversion is based upon formation of a heterojunction between a donor (D) and an acceptor (A) material, which can be two different organic dyes, a polymer and a small molecule, a polymer and an ensemble of semiconductor or oxide nanoparticles, and a host of variations on this theme. 
 
Companies commercializing OPVs include Konarka and Plextronics:
 
[http://konarka.com/  Konarka]
 
[http://www.plextronics.com/index.aspx Plextronics]


*Third Generation Organic Solar Cells
==Solar Spectrum==
With organics and the newer components like the hybrid organic or inorganic cells, you are talking about the 3rd generation solar cells.


[http://konarka.com/  Konarka is one of the first commercial OPV products]
[[Image:Solar_spectrum_current.png|thumb|400px|Solar spectral distribution for one sun. ]]


===Solar Potential===
A broad-band light source is often used to illuminate OPVs under test, sometimes filtered to approximate the output of the sun at the earth's surface (air mass (AM) 1.5 = Air Mass, corresponding to an incident power of 100 mW/cm<sup>2</sup> or 1000 W/m).
[[Image:Direct_normal_solar_radiation_2004.jpg|thumb|300px|This map shows the average irradiance of the US.]]


A sun power generator is used to test the efficiency of organic solar cells. The sun power generator refers to the air mass (AM) 1.5 = Air Mass which also corresponds to the incident power of 100 mW/cm^2 or 1000 W/m.  Questions like “What is the efficiency of your solar cell in terms of transforming that amount of power per cm^2 into electrical power?” come up often. This is referred to as one sun. The sun is considered a blackbody emitter.
This green curve shows solar spectral distribution for one sun (the y-axis units on the right) for standardized conditions. The dips in the bands represent absorption by carbon dioxide and water in the atmosphere. These dips also account for reflectance back towards Earth, e.g. the greenhouse effect.  
===Solar Spectrum===
[[Image:Opv8-spectrum.JPG|thumb|300px|Solar spectral distribution for one sun. ]]
This green curve shows solar spectral distribution for one sun (the y-axis units on the right) for those standardized conditions. The dips in the bands are represent absorption by carbon dioxide and water in the atmosphere. These dips also account for reflectance back towards Earth, e.g. the greenhouse effect.  


The black curve (y-axis on the left) represents the total current density that you have when you integrate from a wavelength of 0. The maximum current density can be calculated by counting all the photons starting from 0 wavelength on the high energy side. This the maximum current density that can be obtained if the power efficiency were to be 100%, or in other words, if for every photon that comes, one electron enters the electrical circuit. This represents a photocurrent 40 milliamps per square centimeter of solar cell area. A few OPVs have begun to approach this but efficiency is still a hot spot for research.
The black curve (y-axis on the left) represents the total current density you could produce in a photovoltaic device, performing the integration up to a certain wavelength. The maximum current density can be calculated by counting all the photons starting from 0 wavelength on the high energy side. This is the maximum current density that can be obtained if the power efficiency were to be 100%, i.e. if for every photon that enters, one electron also enters the electrical circuit. This represents a photocurrent of 40 milliamps per square centimeter of solar cell area. No known solar cells have achieved such current densities without concentrating the sun's power on the solar cell.  Established efficiencies (NREL certified) for OPVs to date are, at best, just under 6%.


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== Advantages of Organic Photovoltaics ==


=== Cost Considerations ===
=== Cost Considerations ===
[[Image:pv_doe_price curve.jpg|thumb|400px|This DOE graph shows price vs. volume of PV production. The brown line shows what the curve might look like with a disruptive new technology such as OPVs.]]


The major driver of new technologies is not only the lack of supply. If an alternative solution for sources of energy that is less expensive than fuel or electricity is found, then everyone will use it as long as the technology is available. However, as of now, that is not the case. The cost of electricity from coal fired thermal plants is about 4 cents a kilowatt hour while silicon solar runs about 25- 35 cents a watt. The price for alternative solutions such has solar cells is still pretty high. For instance, Allen Heeger<ref>http://www.esi-topics.com/conducting-polymers/interviews/Dr-Alan-Heeger.html</ref> has installed a solar cell roof on his house in Santa Barbara but it will take about 7-8 years before it becomes profitable. However, that is still better than losing money from electricity costs every year for the duration or lifetime of the house.
The major driver for the adoption of new technologies is often a combination of a lack of supply of the old technology (e.g. fossil fuels), and the introduction of a "disruptive" new technology. The increased cost of electricity generation from fossil fuels, coupled with climate change issues associated with their use, are driving the search for new forms of energy. The cost of electricity from coal-fired thermal plants is about 4 cents per kilowatt hour, whereas silicon PVs create electricity at about 25- 35 cents per watt (that price continues to fall). The price for alternative solutions such as solar cells is still too high. For instance, Nobel Laureate Professor Alan Heeger<ref>http://www.esi-topics.com/conducting-polymers/interviews/Dr-Alan-Heeger.html</ref> has installed a solar cell roof on his house in Santa Barbara, California. It will take 7-8 years before he is able to recover his initial investment. However, that is still better than paying electricity costs every year for the lifetime of the PV devices.
Metrics: What is most important in terms of the overall production is power conversion efficiency of single cell. With respect to the given input power of the sun, what is the electrical output power that the solar cell can produce? In our case, we will refer to this power conversion efficiency


An economic example: with 5 hours of peak sun per day, 10% conversion efficiency and 10 m2 (1 kW capacity), 5kWh/day, 150 kWh per month, 1,800 kWh per year would product $600 of electricity per year if $0.3 per kWh. The cost of a 1kW capacity system, $7/W, $7,000.
The most important metric is the power conversion efficiency of single cell. With respect to the given input power of the sun, what is the electrical output power that the solar cell can produce?
 
An economic example: with 5 hours of peak sun per day, 10% conversion efficiency and 10 m<sup>2</sup> (1 kW capacity), 5kWh/day, 150 kWh per month, 1,800 kWh per year would produce $600 of electricity per year if electricity cost $0.3 per kWh. The cost of a 1kW capacity system, $7/W, $7,000.


[[Carbon footprint to charge an iPod|Calculate the Carbon footprint to charge an iPod]]
[[Carbon footprint to charge an iPod|Calculate the Carbon footprint to charge an iPod]]
<div id="Flash">Solar cell cost comparator</div> Use this simulation to get a feel for how OPVs could become competitive if the efficiency comes up and the cost comes down.
<swf width="600" height="400">http://depts.washington.edu/cmditr/mediawiki/images/5/54/Solarolympics.swf</swf>


===Efficiency===
===Efficiency===


[[Image:Opvefficiency.png|thumb|300px|]]
[[Image:Opvefficiency.png|thumb|300px|]]
The record in terms of power efficiency for a single cells on the order of 25%. If cells are stacked up with one on top of the other, the power efficiency can reach up to 40%. The material that can produce the best performance and has the highest power efficiency is the III-V. Crystal and silicon has an efficiency of 25% for a single cell. The organics that have started 20 years ago with the work of Xing Tai at Kodak are going up. For polymers, the record efficiency is on the order of 6%. In the case of the Gretal cells that are hybrid organic, inorganic, can have efficiencies of  11-12%. Usually there is too much emphasis on efficiency of the cell because that is certainly not the only parameter that needs to be taken into account in the engineering of the cell and in using it efficiently for the electrical grid. Many of these cells that produce a very high efficiency are also extremely small. Then when solar cells are scaled up to the sizes that are needed to cover a roof the scaling up will lead to issues that will lower the efficiency. So when someone gives you a new record efficiency always pay attention to what is the scale or the area of the cells they are using.
The record power conversion efficiency for single crystal silicon cells is close to 25%. Multi-junction solar cells (created from stacks of III-V semiconductor materials) with concentrators have power conversion efficiencies approaching 40%, but the electricity generated is still not competitive in cost with that generated from fossil fuels.  
[[Image:Efficiency_OPV.jpg|thumb|300px| NREL plot of efficiency of various photovoltaic devices. The red line in the lower right is OPVs.]]
 
Both small molecule and polymer-based OPVs have recently shown dramatic improvements in efficiency, approaching 6%. Dye-sensitized solar cells (DSSCs) are hybrids of nano-porous metal oxides, like titanium oxide, and organic dyes, with solution electrolytes.  DSSCs can demonstrate power conversion efficiencies of  11-12%, however they have proven difficult to manufacture in stable platforms. Ccurrent research is focused on using condensed phase, polymeric charge transport agents, and it would not be surprising if OPVs and DSSCs converge on very similar material combinations and device platforms.  
 
Five percent is considered a reliable efficiency for OPVs at this time. This low efficiency is tolerable if the production expense is small compared to silicon devices. OPVs are projected to become economically viable at 10-11% efficiency.  
[[Image:Pv-efficiency-chart.20190103.jpg|thumb|center|600px| NREL plot of efficiency of various photovoltaic devices. The red line in the lower right represents OPVs.<ref>http://www.nrel.gov/pv/thin_film/docs/kaz_best_research_cells.ppt</ref>]]
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[[Image:Opv-flexible.JPG|thumb|440px|Organic cells use manufacturing techniques similar to OLEDs and printed  electronics  
[[Image:Opv-flexible.JPG|thumb|440px|Organic cells use manufacturing techniques similar to OLEDs and printed  electronics  
]]
]]
Another reason many people have interests in organic solar cells is that flexible modules can be made. For example instead of separate panels, extremely thin conformable films can be used to cover the roof and the solar cells won’t make any visual impact on your roof. Also for many other applications, weight is an issue. For soldier in operations a very significant part of the weight that must be carried is from due to batteries and therefore, being able to have portable power that would be light weight would make a big difference. All these aspects stir great interest in making flexible organic cells.
OPVs are also attractive because of their potential flexibility and light weight. Many off-grid applications in remote areas of the world would be greatly aided by portable power. It would enable you to take your iPod on that next backpacking trip, or disseminate remote sensors throughout the food system, powering sensors that can detect pathogens in real time.


== Manufacturing and Disposal ==
=== Manufacturing and Disposal ===
Organic solar cells may be manufactured with easy to process plastics using standard screen printing techniques rather than the elaborate methods required with silicon solar cells. At end of life they will non-toxic and easy to dispose of.
Organic solar cells may eventually be manufactured with easily processed plastic substrates, using standard printing and screen printing techniques rather than the elaborate methods required with silicon solar cells. At end-of-life they promise to be easily recycled or disposed of.


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===Prototype Fabrication and Testing===
==External Links==
Organic photovoltaic devices are typically built with either the technique of vacuum deposition or spin coating. Either system allows the progressive build up of very thin uniform layers of chemicals and metallics. In spin coating the test surface is coated with a chemical and then spun at high speeds in a centrifuge so that excess material thins out. Vacuum deposition allows building up of layers one atom at a time and permits very precise control over the surface characteristics. Prototype cells are then tested with and "artificial sun" lamp that is calibrated for power.


[[wikipedia:Vacuum_deposition]]


<swf width="800" height="600">http://depts.washington.edu/cmditr/media/opvfab.swf</swf>
[http://www.solarmer.com/solar_technology.php Solarmer - manufacturer of OPVs]


[[category:organic solar cell]]
[http://cs.sbcc.edu/physics/solar/sciencesegment/ Flash explanation of electrons and holes in solar cell]


==External Links==
== References ==
[http://en.wikipedia.org/wiki/Spin_coating Explanation of spincoating process]


[http://www.ipc.uni-linz.ac.at/index.html Videon on OPV manufacturing process]


== References ==
<references />
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<td style="text-align: left; width: 33%">[[Organic Solar Cells|Previous Topic]]</td>
<td style="text-align: center; width: 33%">[[Main_Page#Organic Solar Cells|Return to OPV Menu]]</td>
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http://en.wikipedia.org/wiki/Vacuum_deposition
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<references />
</table>

Latest revision as of 15:34, 7 January 2019

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Although solar energy is a very small component of the overall sources of energy, its use is growing significantly. An exponential increase in the production capacity of solar energy is still needed in order to satisfy the energy needs of today.

This map shows the average irradiance of the US.[1]

Utilization of Solar Energy

The U.S. lags other countries in PV shipments.[2]

A 42% annual growth rate of cumulative installed PV capacity has been fairly steady in recent years and been accompanied by a steady decrease in the price of solar modules (per watt), from nearly $100 in 1976 down to an average of $4. In 2005, for the first time in history, a total of over 1 Gigawatt (GW) of power capacity was added, increasing the cumulative installed capacity to a value of 3.7 GW in established industrial countries. The greatest proportion (85%) was provided by Germany and Japan alone.

"Generation I" (single crystal and poly-crystal silicon) solar cells may be found on roof tops, and in large power generating arrays around the world. The balance of system (BOS) cost is generally larger for off-grid applications because they require a storage device, such as an array of lead-acid batteries. For on-grid houses or industries, solar-generated electricity can be distributed back into the electrical grid when production exceeds the needs of the user.

Organic solar cells (organic photovoltaics or OPVs) are an emerging Generation III technology, providing another lightweight option for off-grid applications (e.g. chargers for portable electronics). OPVs may eventually compete for power generation with Generation I on-grid devices if their efficiencies and lifetimes are high enough, and their costs low enough.

Generations of Solar Cells

Graph of efficiency vs. cost for generations of solar cells. Courtesy of Martin Green


First Generation

Silicon solar panels on a roof

Solar cells currently on the market are almost all Generation I devices made from crystalline silicon, considered to be a "mature" technology. They are somewhat expensive to produce because of the high processing costs needed to create silicon cells with sufficient purity and long range-order. See Types of Solar Cells

Second Generation

Generation II materials are less mature as a PV technology, and are generally created using vacuum deposition or chemical vapor deposition (CVD). These include CdTe or copper-indium-gallium-selenide (CIGS) technologies. Their costs are lower, as are their efficiencies, but they are thinner and lighter than silicon cells. Disposal at end-of-life is a consideration, because of the toxicity of Cd, Te, Ga, and Se, and because of concerns regarding their earth abundance.

See DOE report on solar energy research[3]

Third Generation

OPVs come in several different platforms, and when fully optimized, will be light-weight, low-cost, flexible and easily scalable energy conversion platforms. Their mode of energy conversion is based upon formation of a heterojunction between a donor (D) and an acceptor (A) material, which can be two different organic dyes, a polymer and a small molecule, a polymer and an ensemble of semiconductor or oxide nanoparticles, and a host of variations on this theme.

Companies commercializing OPVs include Konarka and Plextronics:

Konarka

Plextronics

Solar Spectrum

Solar spectral distribution for one sun.

A broad-band light source is often used to illuminate OPVs under test, sometimes filtered to approximate the output of the sun at the earth's surface (air mass (AM) 1.5 = Air Mass, corresponding to an incident power of 100 mW/cm2 or 1000 W/m).

This green curve shows solar spectral distribution for one sun (the y-axis units on the right) for standardized conditions. The dips in the bands represent absorption by carbon dioxide and water in the atmosphere. These dips also account for reflectance back towards Earth, e.g. the greenhouse effect.

The black curve (y-axis on the left) represents the total current density you could produce in a photovoltaic device, performing the integration up to a certain wavelength. The maximum current density can be calculated by counting all the photons starting from 0 wavelength on the high energy side. This is the maximum current density that can be obtained if the power efficiency were to be 100%, i.e. if for every photon that enters, one electron also enters the electrical circuit. This represents a photocurrent of 40 milliamps per square centimeter of solar cell area. No known solar cells have achieved such current densities without concentrating the sun's power on the solar cell. Established efficiencies (NREL certified) for OPVs to date are, at best, just under 6%.


Advantages of Organic Photovoltaics

Cost Considerations

This DOE graph shows price vs. volume of PV production. The brown line shows what the curve might look like with a disruptive new technology such as OPVs.

The major driver for the adoption of new technologies is often a combination of a lack of supply of the old technology (e.g. fossil fuels), and the introduction of a "disruptive" new technology. The increased cost of electricity generation from fossil fuels, coupled with climate change issues associated with their use, are driving the search for new forms of energy. The cost of electricity from coal-fired thermal plants is about 4 cents per kilowatt hour, whereas silicon PVs create electricity at about 25- 35 cents per watt (that price continues to fall). The price for alternative solutions such as solar cells is still too high. For instance, Nobel Laureate Professor Alan Heeger[4] has installed a solar cell roof on his house in Santa Barbara, California. It will take 7-8 years before he is able to recover his initial investment. However, that is still better than paying electricity costs every year for the lifetime of the PV devices.

The most important metric is the power conversion efficiency of single cell. With respect to the given input power of the sun, what is the electrical output power that the solar cell can produce?

An economic example: with 5 hours of peak sun per day, 10% conversion efficiency and 10 m2 (1 kW capacity), 5kWh/day, 150 kWh per month, 1,800 kWh per year would produce $600 of electricity per year if electricity cost $0.3 per kWh. The cost of a 1kW capacity system, $7/W, $7,000.

Calculate the Carbon footprint to charge an iPod

Solar cell cost comparator

Use this simulation to get a feel for how OPVs could become competitive if the efficiency comes up and the cost comes down.

<swf width="600" height="400">http://depts.washington.edu/cmditr/mediawiki/images/5/54/Solarolympics.swf</swf>

Efficiency

Opvefficiency.png

The record power conversion efficiency for single crystal silicon cells is close to 25%. Multi-junction solar cells (created from stacks of III-V semiconductor materials) with concentrators have power conversion efficiencies approaching 40%, but the electricity generated is still not competitive in cost with that generated from fossil fuels.

Both small molecule and polymer-based OPVs have recently shown dramatic improvements in efficiency, approaching 6%. Dye-sensitized solar cells (DSSCs) are hybrids of nano-porous metal oxides, like titanium oxide, and organic dyes, with solution electrolytes. DSSCs can demonstrate power conversion efficiencies of 11-12%, however they have proven difficult to manufacture in stable platforms. Ccurrent research is focused on using condensed phase, polymeric charge transport agents, and it would not be surprising if OPVs and DSSCs converge on very similar material combinations and device platforms.

Five percent is considered a reliable efficiency for OPVs at this time. This low efficiency is tolerable if the production expense is small compared to silicon devices. OPVs are projected to become economically viable at 10-11% efficiency.

NREL plot of efficiency of various photovoltaic devices. The red line in the lower right represents OPVs.[5]


Weight and Flexibility

Organic cells use manufacturing techniques similar to OLEDs and printed electronics

OPVs are also attractive because of their potential flexibility and light weight. Many off-grid applications in remote areas of the world would be greatly aided by portable power. It would enable you to take your iPod on that next backpacking trip, or disseminate remote sensors throughout the food system, powering sensors that can detect pathogens in real time.

Manufacturing and Disposal

Organic solar cells may eventually be manufactured with easily processed plastic substrates, using standard printing and screen printing techniques rather than the elaborate methods required with silicon solar cells. At end-of-life they promise to be easily recycled or disposed of.


External Links

wikipedia:Vacuum_deposition

Solarmer - manufacturer of OPVs

Flash explanation of electrons and holes in solar cell

References

  1. ↑ http://www.nrel.gov/gis/solar.html
  2. ↑ http://www.nrel.gov/analysis/pdfs/46025.pdf
  3. ↑ http://www.sc.doe.gov/bes/reports/files/SEU_rpt.pdf
  4. ↑ http://www.esi-topics.com/conducting-polymers/interviews/Dr-Alan-Heeger.html
  5. ↑ http://www.nrel.gov/pv/thin_film/docs/kaz_best_research_cells.ppt
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