23 Aug 2004
Konarka's thin-film photovoltaics could lead to a whole range of innovative solar-powered products. James Tyrrell speaks to the US company to find out more about the technology.
From Opto & Laser Europe September 2004
Unlike silicon-based PVs, first developed by US-based Bell Labs in the 1950s, Konarka's products use photoactive dye to convert light into electricity. Resembling photographic film, Konarka's flexible plastic PVs contain a layer of dye-activated titanium dioxide (TiO2) particles and can be mass produced on a roll-to-roll process.
"What we are bringing forth is not a semiconductor-fab-type technology," Daniel McGahn, Konarka's executive vice-president and chief marketing officer, told Opto & Laser Europe. "It can be done in the ambient environment, it can be done in a warehouse, it doesn't have to be done in a class 100 cleanroom."
The theory Light falling on the PV film passes through a clear plastic barrier layer and a conductive electrode layer to reach a dye-impregnated composite TiO2 particle region (see figure, p26). The dye reacts with incoming photons, releasing electrons into the semiconducting TiO2 network, which is in turn connected to a counter electrode.
As well as being thin and flexible, Konarka says that its PVs work well in low-light conditions and under artificial light. The dye can also be tuned to absorb specific wavelength bands and Konarka has achieved efficiencies that make commercial devices feasible.
"At the lab level we're near 12% [photon to electron conversion]. The manufacturing level is nearer 8%, but what we're going to market with is a 5% film because we think that's what the initial threshold for the market needs," commented McGahn.
To put this into context, the conversion efficiency of commercial mono/polycrystalline silicon-based PVs is about 15%, with values approaching 30% for triple-junction cells containing a mix of semiconductor materials and using concentrators. Konarka plans to use its film's flexibility, appearance and low manufacturing cost to win market share from amorphous silicon devices that offer similar conversion efficiencies of 5-7%.
The breakthrough that led to Konarka's first prototypes came when founding scientist Sukant Tripathy (see box, p28) and his researchers were able to reduce the temperature of the TiO2 sintering process. The team found a way to convert single TiO2 particles into a conductive network at 150ºC instead of the previous temperature of 450ºC. At 450ºC the choice of substrates was limited to rigid and often delicate glass materials. The new "cold sintering" technology transformed the number of possible applications and the manufacturing process itself by allowing the use of flexible plastic substrates.
"There's a little art to exactly how they [TiO2 particles] are pre-conditioned," McGahn told Opto & Laser Europe, careful to protect the firm's proprietary knowledge. "The real trick is that there's a uniformity to the [particle] size. These are all nanoscopic of the order of tens of nanometres in diameter."
With several key R&D and production staff coming from Polaroid, it is no secret that Konarka's fabrication methods are rooted in the photographic-film industry. "What we are starting with is a very simplified version of a roll-to-roll coating process," McGahn pointed out.
Exciting developments There are some interesting technical developments taking place behind the doors of Konarka's labs. "What we get very excited about, but it's at the research level, is the idea of being able to do the same coating process on a fibre," McGahn explained. "Instead of coating multiple layers on a flat surface, you could dip a fibre through different solutions to create a PV fibre."
Being able to weave "solar" fibres into textiles could open up a huge market for PVs, essentially the opportunity to power anything that needs a battery. "It could be an ipod, it could be the rifle sight for an infantryman," suggested McGahn.
Although it may be a few years before these applications are realized, Konarka's business plan is now in full flight. Despite having its headquarters in Massachusetts, US, the firm's business activities have a strong European focus.
"Germany is the second largest photovoltaic market today, Japan being number one," said McGahn. "Europe as a total, from a continent standpoint, is the largest PV market." The US firm's European presence extends to research operations in Linz, Austria, and Zug, Switzerland, with another facility due to be announced in Germany.
Boosting renewable energy Europe's political climate is also seen as receptive to "green" power such as solar energy. The European Commission aims to double renewable energy's share of gross domestic energy consumption from 6 to 12% by 2010.
Forecasts suggest that by then, 21% of France's electricity generation will involve renewable energies. "We have a partnership with Electricité de France (EDF), who would like to be a consumer of these products," said McGahn. With 41.6 million customers worldwide and 35.6 million in Europe, EDF is a big hitter in the energy business.
"We won't necessarily go to the market as a traditional photovoltaic [supplier]," McGahn told Opto & Laser Europe. Instead, Konarka's plans involve growing to a size where it can join forces with global companies to focus on a specific use. For example, say a car manufacturer wanted to launch a new model featuring PVs, Konarka's goal would be to work with the firm to marry its material to the final product.
The low cost of fabrication equipment places Konarka in a position to offer application-specific production to the point where manufacturing could even take place in-line at a customer's premises.
In a US radio interview on THE Business Station, Konarka's chairman and chief executive officer Howard Berke told listeners that the firm plans to generate revenues in 2005, becoming profitable in 2007.
Company background The founding of Konarka was inspired by the work of Sukant Tripathy. During his 15 years at the University of Massachusetts, US, Tripathy established himself internationally in the field of material science. He was a major force in creating the University's Institute for NanoScience Engineering and Technology, raising the university's profile in the emerging nanotechnology sector - a cornerstone of Konarka's technology.
Born in India in 1952, but spending most of his professional life in the US, Tripathy's vision was to produce low-cost power that could be deployed in the developing world, specifically India. Tragically it was a dream that he never achieved as he drowned while swimming at the Pololu valley, Hawaii, in 2000. Konarka takes its name from one of Tripathy's favourite places - the magnificent temple dedicated to the sun god Surya in Orissa, India.
Along with Tripathy, Konarka's intellectual contributors include Nobel laureate (chemistry, 2000) Alan Heeger and dye-based photoelectric cell pioneer Michael Grätzel. Building on this knowledge and expertise, the company has amassed a strong intellectual-property base, featuring more than 75 patents, developing technology both in-house and licensing-in from EPFL Lausanne, Switzerland, and the University of California Santa Barbara and Dupont in the US.
Konarka - key facts
Headquarters: Lowell, Massachusetts, US
Funding: $32 m