January 08, 2006
Organic Photovoltaics Absorb From Near Infrared Frequencies
A research group has developed organic nanostructures photovoltaics that can absorb photons near the infrared frequency.
Ewing, NJ | 4 January 2006 -- Global Photonic Energy Corporation (GPEC), developer of organic photovoltaic (OPVtm) technology for ultra-low cost high power solar cells, announced that the company's research partners at Princeton University and the University of Southern California (USC) have achieved a new record in an organic solar cell that is responsive to light in the near infrared (NIR) range of the solar spectrum. NIR radiation is invisible to the human eye.
Many so-called "night vision" devices operate by sensing infrared light which is emitted by warm objects and makes up a substantial portion of all energy reaching the earth from the sun. Under only NIR radiation, the Princeton solar cell would appear to be generating power in the dark -- as the human eye is only sensitive to visible light.
This latest achievement is the highest level of conversion performance yet achieved for an organic solar cell in the IR portion of the solar spectrum. The Company's researchers detail this latest achievement in the December 2 issue of Applied Physics Letters.
The Global thirst for energy is continually expanding. Renewable energy sources have experienced rapid growth in recent years as costs have improved. Global solar cell production has grown over 20% annually for the last 20 years, reaching sales of $6 billion in 2004. This strong growth has resulted in a world-wide shortage of semiconductor silicon driving 2005 solar cell prices higher. Cost is a critical factor in the continued expansion of the solar cell industry. Currently, solar-generated power is four to six times more expensive to consumers than coal-generated power.
Silicon crystals are too expensive as a starting material for making photovoltaics cells. The development of organic photovoltaic materials holds the potential for much cheaper photovoltaics. These Princeton and USC researchers (see below) are not only pursuing organically based photovoltaics but they are also pursuing the development of much higher efficiency photovoltaics. The odds are developing a way to double or triple the conversion efficiency of organic photovoltaics will not increase costs per square meter of materials anywhere near as much. So cost per unit of energy produced will drop.
Recent efforts have focused on the use of "organic" materials. Organic semiconductors contain the ubiquitous element carbon and are capable of achieving ultra-low cost solar power generation that is competitive with traditional fossil fuel sources. Organic materials have the potential to achieve ultra-low cost production costs and high power output. The materials are ultra-thin and flexible and can be applied to large, curved or spherical surfaces. Because the layers are so thin, transparent solar cells can be applied to windows creating power-generating glass that retains its basic functionality.
GPEC sponsors research by Professor Stephen R. Forrest at Princeton and Professor Mark E. Thompson at USC. Professor Forrest's research team has focused on organic "small-molecule" devices that are assembled literally a molecule at a time in highly efficient nanostructures. These devices have layers and/or structural elements that can be extremely small -- at only 0.5 billionth of a meter thick and can be applied to low-cost, flexible plastic surfaces.
These scientists want to boost absorption of photons near the infrared frequency range because that is where much of the energy in sunlight is found.
One challenge for organic solar cells has been the efficient capture and conversion of sunlight. Sunlight consists of photons (particles of light) that are delivered across a spectrum that includes invisible ultraviolet (UV) light, the visible spectrum of colors -- violet, indigo, blue, green, yellow, orange and red -- and the invisible infrared or IR spectrum. The amount of incoming photons across the UV, visible and IR spectrums is about 4%, 51% and 45%, respectively. The photons absorbed by a solar cell directly impacts the power output. To achieve high power output, solar devices must take advantage of as much of the solar spectrum as possible. Typical organic solar cells absorb only a fraction of the visible portion of the solar spectrum. In fact, the best organic solar cells absorb and convert only about 1/3 of the total available light utilizing primarily the visible portion of the spectrum.
"This latest device demonstrates that significant power can be harvested from the IR and near-IR portion of the solar spectrum.", said Dr. Stephen R. Forrest. "In fact, this novel approach has the potential to double the power output of organic solar devices with power harvested from the near-IR and IR portion of the solar spectrum. With this approach we are well on our way to power levels exceeding 100 watts per meter", Forrest concluded.
Imagine organic photovoltaics coating windows especially in hot climates. Instead of letting in the infrared frequencies the photovoltaics convert those photons to useful electricity. So instead of heating a building and thereby increasing the demand for air conditioning the photovoltaic coating could keep out heat and turn it into electricity that would power air conditioners.
In the longer run imagine nanomaterials-based photovoltaic coatings that could adjust how much electricity they let into a room or into a car depending on whether a human was in the room or car. When a human was present the material could become transparent to allow ing lighting or provide the ability to look outside. House and car windows could be turned dark or transparent by dynamically changing nanostructures. When no one was in a car or house room the windows could become dark and that would mean the nanocoatings were absorbing the light that hit them and turning them into electric to charge batteries (which of course will be made from some nanomaterials as well). So on a hot summer day your car's seats wouldn't get as hot. Also, the inside trim wouldn't degrade as rapidly due to sun damage.
GPEC is funded by electric power industry venture capitalists Kuhns Brothers.
Well, if we're dreaming of what may someday be possible, why should we stop at window coatings that let in visible light and produce electricity from near infrared? Isn't it kind of silly to think that our future solar electricity will be running air conditioners rather than that there might be new HVAC techniques that make today's air conditioners unnecessary? I like designing airflows to reduce heating and cooling and increasing air quality. I wonder if radiant heating (and cooling) wall hangings might be useful in this kind of future. Hell, I wonder if they might be useful (and possible) now.
To me, this is kind of like saying "Let's build lots of state of the art nuclear power plants specifically so we don't have to change from incandescent to more efficient lighting tech." It's symptomatic of imaginative failure.
If you're gonna dream of the future, follow through on your dreaming at the very least. Please, don't just stop and gawk over the newest and latest discovery like it's a locked door.
Well, you can sit on it, literally. The human body emits enough wattage in heat to power a light bulb. Recapture this energy from thousands of poly sci and law students at the lecture hall, and you can reduce the air conditioning more effectively than they would as conservation lobbyists.
A perennial problem with organic PV cells is stability. UV photons are energetic enough to break bonds, and complicated molecules will also tend to decompose or react when heated. This was already a problem with amorphous silicon and with the transparent organic encapsulants used in some PV modules.
jimcrack: you are confusing near IR with far IR. The IR from the human body is mostly the latter. Any PV receptor using such low energy photons would have to have a very low bandgap, so it would have to be cryogenically cooled to keep from dissipating the generated carriers (thermal excitation would enable them to jump back across the diode at room temperature). This shouldn't be surprising; if a PV cell could generate electricity from ambient photons in thermal equilibrium, it would be a perpetual motion machine of the second kind. Solar PV exploits the fact that the spectral temperature of sunlight is much higher than the temperature of the collector.
Personally, I like the idea of something absorbing IR and passing most of the visible spectrum through. In my case, I'm thinking about vehicles. While air conditioning consumes a signficant amount of energy in a household, it also consumes a considerable amount in a vehicle (there's a noticeable difference in my fuel mileage when I'm running the a/c compressor). Imagine "window tint" which will absorb the IR (thereby keeping the vehicle a lot cooler on sunny days), pass most of the visible spectrum through (many states have legal limits to how much light can be blocked) and make electricity.
Now, apply this to the rolling greenhouses known as minivans, station wagons and crossover vehicles. The a/c doesn't have to work as hard (if at all), and you might be able to shut off the alternator on a sunny day. For some vehicles, you can boost your fuel mileage by 10% by shutting off the alternator and running off the battery. You will, of course, run down your battery if you do this long enough, but you get the idea.
Chevrolet was making a "Montana" edition of a minivan which, for a while, had the ability to go over 100 mph. The reason was that, at the time, Montana didn't have a set speed limit on some of its interstate highways ("safe and reasonable" was the speed limit; if you could safely do 150 mph, it was allowed; don't know if that has changed). The minivan in question would shut off the a/c compressor as needed to provide more power, so you could maintain a higher speed. The reviewer of the vehicle described it as "the world's fastest-moving greenhouse," because you sweltered pretty badly once the a/c shut off.
At the North American International Auto Show, Ford was showing off a diesel-electric hybrid which had solar panels built into the roof; with solar assist, it was supposed to get up to 65 mpg. At least one company is making flexible solar panels which can be retrofitted to a Prius, helping improve the fuel economy. This would be a relatively easy retrofit for an existing vehicle, and it would be especially useful for many, existing vehicles.
Paul D -- Thanks for the tip on near v. far infrared, and I don't seriously think anyone will sit still in an expensive solar suit anyway: It would make today's debate on body armor in Iraq look like a fashion statement. Sweat accumulation is the reason why both types of clothing are a problem. But isn't IR collection best employed as a way of improving the efficiency of conventional PV? Strictly speaking, photo voltaics are not photo, because the visible light spectrum is not used, and only comprises 5% of the energy we get from the sun on a bright day. However much a PV remains relatively cool in relation to sunlight, some of the energy must be lost within the wafer material, or reflected out, and thus re-reflectable back into the wafer in the manner of a black-body.
I would like to know whether fitting the back of a solar panel with the new technology might have a trimtab effect at improving performance. An IR back panel absorbs energy, assisting the cooling effect on the PV, increasing voltaic efficiency. Or at least put IR PV around solar heat reflectors and hot fluid chambers. Could the integrated technologies provide an edge during periods of shallow sun angles? Could the added assembly steps and compositing of materials have payback?
Or is PV technology too delicate and complex to lend itself to the kind of mechanical engineering that has benefitted engines, turbines, and cogeneration? And how much near IR is there to collect? Even if there is a lot, wouldn't the lack of it from a single point source be a problem? (back to the tight-fitting clothing analogy, and to the slightly cloudy day)
I Don't pretend to know very much about the physics behind this for i am only just doing a Physics qualification at 17. I was thinking that for my project I might investigate using a normal heat solar cell combined with a solar cell to create a double use for the area to create electricity and water heating. If anyone has any information, ideas or input could reply that would be great. The only other idea I had reading the page was whether the electromagnetic spectrum could be separated into the appropriate groups. One for the photovoltaic cells and the rest of the spectrum that would not create electricty could be used to heat the water. This could theortically be achieved by using prisms and fibre optics.
The heating of the water could also be used to create electricty by using a stirling Engine. Also if anyone knows what frequencies are utilised by the silicon cells that would be helpful. Any useful websites on this that anyone knows would also be much appreciated
Glass blocks IR thats why your car gets hot. Light is absorbed by the interior and re-emitted as IR which is blocked by the glass. The only advantage this coating would have would be to generate electricity to help cool the car, it won't help cool the car by blocking IR.