News

July 25, 2008

Next Generation Dye Sensitive & Organic PV, Part 1

By: by Andrew K. Burger, International Correspondent, Renewable Energy World

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Registering as just a 'blip' on the renewable energy and solar power radar screens only a few years ago, organic and hybrid dye-sensitized thin-film photovoltaic (PV) cells are attracting growing interest and investment.

Cutting-edge companies such as G24 Innovations, Konarka, Dyesol and Denmark's Heliotech are commercializing the first generation of products that incorporate hybrid dye-sensitized thin-film (DSC) and organic PV (OPV) cells while continuing to drive advances and improvements in manufacturing and process technology in order to develop new commercial applications, address cell durability issues and drive down costs, as well as increase cell conversion efficiencies.

On the materials supply side of the nascent industry, companies such as Carnegie Mellon R&D spin-off Plextronics are advancing with efforts to commercialize and enhance their ability to produce organic, nanoengineered conductive and semi-conductive inks that are used to manufacture both DSC and organic PV cells, as well as a growing range of printed electronic circuitry.

Their flexible form factors, low cost and ability to capture photons and convert them into electricity both indoors and in poor lighting is paving the way forward for DSC and OPV cells to be used in various and numerous applications.

Their promise was brought into sharper light recently when an MIT research team increased PV cell conversion rates ten-fold by coating panes of glass with transparent photosensitive dyes that concentrated solar energy at the edges of the panes. PV cells in the window frames then converted the concentrated flow of photons into electricity.

The market for thin-film and organic photovoltaic (PV) materials will reach US $3.8 billion by 2015, according to a March research report produced by NanoMarkets. Advances in thin film and organic PV - which typically includes DSC - are creating opportunities for electronic chemical suppliers and innovative materials firms, according to Nanomarkets' research, noting that predicted materials innovations are expected to have a profound impact on PV's future.

Organic Light Emitting Diodes & Printed Circuitry

Organic light emitting diodes (OLED) and DSC-based equipment chargers, as well applications in portable electronics in general, are attracting particular interest, as is incorporating DSC and organic PV cells into a range of textile products, including outdoor equipment, such as tents and backpacks. However, because it is still early in the game, it remains to be seen to what scale and scope such products can be commercialized, NanoMarkets cautions.

"One bit of organic PV that is truly commercialized is OLED," explained NanoMarkets' analyst Lawrence Gasman. "There are OLEDs in the multiple hundreds of millions out there and there's been a lot of talk about OLED TVs. A number of companies have brought them out, but where you have seen OLEDs for a long time now is in very small displays - MP3 players, sub-displays in cell phones. Pioneer's been using them for their in-car stereo units."

While nearly all OLEDs are currently produced using vaporization technology, "there are increasingly hopeful signs that printed OLEDs [will replace vaporization], and that the same technology can be applied to OPV," a tack being taken by Cambridge Display Technology, Gasman noted.

Organic PV and conducting inks open up wide new vistas that extend from OPV cells to printed electronic circuitry. At the recent IDTechEX "PV Beyond Conventional Silicon" conference in Denver, Plextronics announced that it was making available two versions of its Plexcore ink systems for organic solar cell production available in research quantities.

The company was already working to fill multiple orders by the end of June. Plexcore OPV inks are based on the company's record-setting nanoengineered technology, which recorded 5.4% conversion efficiencies in independent OPV cell testing conducted by the National Renewable Energy Laboratory.

Looking Down the Line

Looking further down the line, potential applications for DSC and organic PV also abound in building-integrated PV (BIPV), as well as building and construction products, from windows to paints and cladding.

DSC and organic PV manufacturers see a potentially bright future for their products on rooftops, on windows, and more generally in the BIPV space as government building authorities increasingly enact LEED and new building code amendments that require on-site renewable power generation. Konarka, for example, is looking at rooftop solar application of its organic PV cells and has garnered funding from the U.S federal government's Solar America Initiative, as has Plextronics.

"The big advantage of organic PV cells is that they can be very, very cheap. A plastic solar cell - think of the ubiquity of cheap plastic products. The projected cost of organic solar cells is in the less than US $0.40 cents/watt range as compared to US $3-4 dollar/watt range for other solar technologies," commented Dr. Pradap Haldar, director of Energy & Environmental Technology Applications (E2TAC) and head of the nanoengineering constellation at the University of Albany's Center for Nanoscale Science & Engineering (CNSE).

Plextronics believes the organic PV inks it is developing can cut PV cell production costs by as much as 75%. "One of the most striking statistics that I can give you is this: The cost to produce a watt of energy right now using current solar technologies is about $4 per watt. Using Plextronics' technology, we believe that you can reduce that to around $1 a watt in high-volume manufacturing.

"In some applications, organic solar cells will compete with other technologies on a straight cost versus performance basis. But other applications will be unique, such as ‘integrated products' where printed organic solar cells are incorporated into products right along with other printed electronic components such as transistors, for logic and memory, and light emitting diodes for information displays or indicators," Plextronics spokesperson Lori Lecker said.

"A myriad of products are envisioned ranging from smart cards to advanced RFID tags to interactive consumer product packaging and toys...Also, organic solar cells are unique in that they can be made semi-transparent, opening up new applications such as building windows," added VP of products Troy Hammond.

Where It Was Born: DSC and OPV Intellectual Property

The growing interest and activity in the organic PV and DSC spaces can be traced back to the efforts of just a few companies, Nanomarkets' Gasman elaborated. "Konarka is clearly a leader due to IP (intellectual property), partly of their own development and partly due to acquiring Siemens IP through their acquisition of that business.

"They've (Konarka) now opted to focus primarily on the pure organic area. They've basically licensed their DSC technology to a company called G24i in Wales. The other big player [in DSC] is Dyesol, which has original research and IP. Those three companies account for a lot of what's gone on in this field."

Much of the seminal IP related to DSC that was originally created in 1991 by Michael Graetzl and Brian O'Regan and still being refined and developed at the Ecole Polytechnique Federale de Lausanne (EPFL) is now being tested, improved upon and commercialized by Wales-based G24i. "In terms of commercialization, we're much further along [as compared to organic PV]," commented G24i chairman and co-founder Robert Hertzberg.

"Basically, we have a license from EPFL; then we have a sole license with respect to Konarka in terms of proof-of-concept testing, and we have added about 25 patents to it. There's a big gulf between lab production and industrial production. We've been at it now for almost two years putting it all together...We have contracts to sell and production has started."

Conversion Efficiencies

Skeptics and critics point out two major disadvantages to OPV when it comes to comparisons with current silicon-based technology, explained E2TAC's Haldar.

The primary skepticism relates to their comparatively low light-to-electricity conversion ratios. The DSCs G24i is using in its first-generation chargers comes in around 2-3% while Pittsburgh-based Plextronics' and other cutting-edge DSC and OPV cells convert anywhere from 5-8% of incident sunlight into electrical power in laboratory testing conditions.

"Five to six percent efficiencies can usually be obtained in very controlled conditions, though some [tests] have not been validated independently," Haldar noted. "Some people don't even believe those very high results. Typically, 3-4% easily obtained. Some of the highest numbers are subject to skepticism. (For more on verifying efficiency claims of organic PV, listen to Stephen Lacey's May 29 podcast that looked at the subject.)

"To me, if you look at it from a commercial standpoint, these championship numbers are for naught. What good are these numbers if you can't get them out in the field?"

G24i's Hertzberg would agree, but looks at test results from a different practical perspective. He believes that industry focus on conversion efficiencies is based on traditional comparisons with grid power and that hence, their use is ill-conceived and misguided when it comes to the new types of off-grid, personal and portable applications G24i and others in the DSC and organic PV space are targeting.

"Two questions that typically come up from people in traditional industry are ‘What are your cost/watt and ‘What are you efficiency ratings?'" Hertzberg said. These are statistics used by fixed-base roof-mounted industries to compare them to coal and hydro on a grid-based system."

Arguing DSC's case, Hertzberg typically makes two additional points, "One is environmental degradation: There's a US $53 billion battery industry globally. North of $45 billion of that is industry making batteries that take over 30 times the energy to make then they can store, and then there are all the waste and disposal issues."

"At the end of the day, the customer is interested in having enough power to power what he or she needs to power, not efficiency numbers," Hertzberg maintains. "We think there's room for everybody. Our competition is in the fossil fuel and battery industries."

"Current technology is in the 5-6% range for small research-sized solar cells. We believe this efficiency is adequate for early niche applications of organic solar cells," commented Plextronics' Troy Hammond. "The activity of increasing this and scaling it to large areas is under way."

Another potentially misleading aspect is the way conversion efficiencies are measured. G24i's DSC cells can operate indoors and under low light conditions, greatly extending the period of time they are producing electricity. They can also capture the energy inherent in light waves striking the cell surface from wider angles of incidence, both of which compensates for their lower efficiencies.

Using the same conversion efficiency ratings to compare very different attributes and performance characteristics of DSC and OPV to traditional silicon PV and conventional power generation technology is "the wrong question; it's not relevant for commercialization [of DSC] because if you're in a flexible form and mobile product environment, it's about how much of a trickle charge you can get in a 24-hour space," Hertzberg asserted.

"It's like solar power and thin film or the tortoise and the hare. Though we move a lot slower so to speak, DSC's can come out ahead at the end of the day [in terms of the amount of electricity they can reliably deliver to people and homes]."

Durability

Durability is the second hurdle OPV products have to overcome. OPV cells "tend not to be stable. For example, silicon solar cells can last 25-30 years. If organic solar cells are exposed to excessive UV (ultraviolet) radiation, even sunlight can degrade them in a matter of days. Excessive humidity and moisture can do likewise, Haldar pointed out. "It's a real stumbling block for organic PV. People are working frantically to address those issues."

Leading OPV participants such as G24i, Konarka and Plextronics, are more than well aware of the durability issue. They're focusing on addressing it and can point to recent efforts that indicate they can succeed.

"Durability means lifetime for us, and that is a very important focus of ours right now," Plextronics' Lecker commented. "While we can't get into the specifics, I can tell you that we are aiming significant time and resources at improving the lifetime of OPV."

Part 2 of this article will look at G24i's "Lighting Africa" project and is part of RenewableEnergyWorld.com's Renewable Energy in the Developing World series.