The Growing Market for Solar Cells
Printing is playing a key role in the development of low-cost flexible thin-film solar cells, and ink companies are creating novel new technologies for this fast-growing market.
By David Savastano
As petroleum-based energy costs soar and concerns over the environment as well as sustainability
First Nanosolar utility panels shipped and deployed in Germany in a free-field plant installation. (Photo credit: Willi Breuer)
Solar technologies have generated tremendous interest among the public and investors alike, and the allure is understandable: the ability to harness the sun’s energy offers unlimited clean power.
The goal, then, is to be able to gather this power efficiently at a reasonable cost. Typically, solar cells are costly, but if a way could be found to mass produce these cells, there could be fast growth in the market. This is where printing comes into play.
It is becoming apparent that flexible thin-film photovoltaic (PV) cells can be used to collect solar energy at a fraction of the cost of present technologies. A wide variety of companies are in the market: United Solar Ovonic (a wholly-owned subsidiary of Energy Conversion Devices Inc.), Global Solar, First Solar, Nanosolar, Konarka, Solopower, HelioVolt, Miasole, Daystar and Evergreen Solar are just a few of the companies in this growing field.
A look at the investments into these companies shows the potential for the field. Nanosolar has received $500 million in funding to date, including investments from leading power companies such as AES Corporation, EDF and the Carlyle Group. Meanwhile, Dow Chemical is partnering with Global Solar.
There is plenty of expansion as well. First Solar announced plans in August to add 500,000 square feet to its manufacturing and R&D facility in Perrysburg, OH. Global Solar just moved into its new 100,000 square foot factory in Tucson, AZ.
Sales are up as well: in terms of publicly-held companies, First Solar’s sales grew to $267 million in the second quarter of 2008, up from $77.2 million in the second quarter of 2007. Evergreen Solar reports that it has $3 billion worth of orders from five customers for the next five years, most recently signing a $1.2 billion contract with IBC Solar AG.
The Market for
Printed Solar Cells
The development of printed solar cells is moving forward more quickly than originally anticipated.
“Organic printed solar cells are rapidly evolving as a third generation photovoltaic material,” said Dan Williams, vice president of business development for Konarka. Mr. Williams noted that Konarka’s Power Plastic material was originally thought to be viable by 2010, but it is finding immediate markets for today’s renewable energy applications in everything from consumer portable charging to flexible outdoor structures.
Nanosolar CEO Martin Roscheisen said the printed solar cell market was non-existent until recently because all of those solar cells that could be printed were either based on inefficient or unstable semiconductors.
“Only with Nanosolar working out ways of printing CIGS, the most efficient and most stable thin-film semiconductor, has it been possible to bring the economics of printing to solar in a way that has large market reception,” Mr. Roscheisen said.
“While thin film solar cells have begun to make an impact in the market place, currently they are led by vapor deposited technologies,” explained Troy Hammond, vice president of products for Plextronics. “Truly printed solar cells are on the verge of commercialization.”
Because of the potential for the thin film PV market, there is plenty of interest from the financial end.
“The thin film photovoltaic market has a lot of venture capital going into it,” said Stuart Ganslaw, vice president of business development, Creative Materials, Inc., a supplier of conductive inks, coatings and adhesives. “It’s a matter of who is getting the funding.”
The technologies are varied, ranging from high-efficiency, low-cost copper-indium-gallium-selenide (CIGS) utilized by Global Solar, Solopower, HelioVolt, Nanosolar, Miasole and Daystar. First Solar specializes in cadmium telluride (CdTe). United Solar Ovonic utilizes amorphous silicon.
Inks are playing a key role in these products, as established and specialist companies alike are developing exciting new technologies.
“Most of these companies use ink products in the manufacturing process,” Mr. Ganslaw noted. “For PV suppliers, better conductivity is a key, as it enables them to use less ink as well as thinner lines, which improves efficiency by covering less of the cell. Good adhesion and heat resistance are also important, as is environmental stability. It’s a tough application, and it has become a very active area for us.”
“Growing demand for clean energy has resulted in a dramatic increase in demand for solar cells,” said Colin Davie, director, business development, for Sun Chemical. “Sun Chemical views this market and the field of printable electronics in general, as strategically important growth opportunities.”
To help develop inks for the PV market, Mr. Davie noted that Sun Chemical has created a dedicated electronic materials market development group and recently invested in a new, state-of-the-art, 5,000 square foot clean room research and development center in Carlstadt, NJ where the company can print, fire and characterize solar cells.
The inks used for PV cells are highly engineered, in order to provide the efficiencies needed to effectively collect solar energy. For example, Mr. Roscheisen pointed to high efficiency and stability as key properties for inks.
“Key properties for inks would fall into two categories – those which support processing and uniform application and appearance,” Mr. Williams said. “In the case of printed electronic inks for photovoltaics, the ink properties are driven more by functionality (electrical, lifetime, etc.) rather than appearance. This focus on functionality drives the rheological properties of the inks.”
Plextronics’ Plexcore polymers and printable inks are key ingredients in the formation of high-quality organic layers. Mr. Hammond said that improving the performance of printed solar cells begins with the inks that absorb the sun’s light and enable efficient generation of energy, typically referred to as the active layer inks.
“These inks must be solution-processable using traditional large-area printing processes such as gravure, slot-die and inkjet printing,” Mr. Hammond noted. “Critical ink parameters that typically differ between these printing processes include, for example, solvent compatibility, viscosity, vapor pressure and surface tension. Solution processing is the key to low-cost manufacturing due to lower energy requirements and cheaper capital equipment compared to today’s silicon-based vacuum processing.
According to Mr. Hammond, the OPV inks must maintain functionality while being printed via these large-area printing processes. “Layer thickness of these thin films, which is typically 100s of nanometers, is critical to light absorption,” he added. “In addition, both the surface and bulk properties of these thin films, such as surface roughness and morphology, are critical to charge transport and achieving highly efficient device performance. The combination of processibility via economic printing methods and high functionality within the printed device are critical parameters for the inks used in the printed solar cell market.”
Nanosolar CEO Martin Roscheisen holding up a Nanosolar solar cell and a vessel with Nanosolar’s nanoparticle ink in Nanosolar’s facility. (Photo credit: Bart Nagel)
“The screen pastes developed for this market must be printable at a relatively high speed and form dimensionally and environmentally stable conductors,” Mr. Davie noted. “Other desirable properties include low bowing for the aluminum pastes and lead- and cadmium-free formulations for ‘greener’ solar power generation.”
Some of the leading innovators are moving ahead with new technologies in preparation for further expansion in the rapidly growing PV market.
“Over the past year, Konarka has made significant progress in understanding the processing requirements of printed electronic inks to support our production scale up plans,” Mr. Williams said. “Significant investments in process engineering and manufacturing equipment bode testimony to our commitment and confidence in manufacturing printed solar cells for a wide variety of applications.”
“Plextronics has developed a proprietary, leading set of inks for organic photovoltaics (OPV), that is, solar cells where the active layers are made of organic molecules instead of the typical heavy metals and inorganic semiconductor materials,” Mr. Hammond said. “Research cells made using these inks have been certified as the world record performance for OPV by NREL. By combining these inks with process technology and device design, Plextronics can support other companies that are interested in scaling up module manufacturing for this new solar technology. Plextronics’ ink-based business model is unique in the solar cell industry. Other companies are developing inks to enable printing of their own solar modules – only Plextronics in enabling many companies to print solar products by buying the necessary active layer inks. Plextronics formally launched its first ink product targeted to these customers in June of this year and has received very positive response. We foresee customers using our inks and technology first to produce products for off-grid and consumer markets. With continued advancement of the technology by Plextronics, customers should be able to scale up to large-scale on-grid power applications.”
What, then, is the overall potential for the flexible thin film solar cell market?
“There are a number of near-term applications for printed photovoltaic material being developed at Konarka, many being driven by the properties offered by a printed solution such as flexibility of printed substrates, ease of handling, recyclability, high volume production and low cost,” Mr. Williams said. "These features and benefits afford Konarka's Power Plastic to be a viable solution for many applications underserved by more traditional photovoltaic materials. As the demand for ubiquitous power and everything energy-capable increases, the use of printed electronic inks to address those demands will be on the rise.”
“Plextronics believes that solar technology will grow enormously in the coming decades to the point that it is a major contributor of global energy needs,” Mr. Hammond said. “For this to happen, substantial breakthroughs in cost and performance must be achieved. This will be enabled by low-cost printing of ink-based solar technologies such as Plextronics’ organic solar technology.”
“It has the potential to completely dominate solar technology,” Mr. Roscheisen concluded.