Printed Flexible Solar Cells Provide Embedded Renewable Power

In the effort to produce inexpensive, easily manufactured sources of sustainable, renewable power, solar cells continue to be a major focus — particularly flexible solar cells that can be applied directly to surfaces. Flexible solar cells are nothing new, but the methods by which they are made have progressed significantly in recent years.

One company, Konarka Technologies of Lowell, MA, recently announced that they had demonstrated the ability to manufacture solar cells by inkjet printing. The company’s Power Plastic® solar cell technology — which is the result of a project originally funded by the U.S. military — uses a wider range of the light spectrum than conventional solar cells. All visible light sources — not just sunlight — can be used to generate power. It can be used virtually anywhere there is a light source and a battery.

Dr. Christoph Brabec is Chief Technology Officer at Konarka, and previously worked in polymer photovoltaics at Siemens. As a polymer scientist, he helped develop the nanomaterials that are the basis of Power Plastic. He holds 30 patents. NASA Tech Briefs talked with Dr. Brabec about the company’s technology, and the potential impact their novel inkjet printing technique could have on producing low-cost flexible solar cells for a myriad of commercial and industrial applications.

NASA Tech Briefs: How did the U.S. military project lead to the founding of Konarka in 2000?

Dr. Christoph Brabec: In 2000, the U.S. Army provided funding for an elite team of scientists under the coordination of the Army’s Natick, Massachusetts Laboratory to develop advanced photovoltaic technology for soldiers. The team achieved a remarkable breakthrough.

They discovered a new technology to facilitate materials processing at relatively low temperatures. This discovery enabled, for the first time, the use of a wide variety of low-cost polymers as the top and bottom surfaces of the photovoltaic cell. It also enabled the photovoltaic cells to be manufactured at a much higher speed. The resulting plastic- based photovoltaic cells are efficient across a much broader spectrum of light than traditional solar cells, allowing them to be useful indoors as well as outdoors.

This breakthrough led to the founding of Konarka in July 2001. The revolutionary chemical process and the roll-toroll manufacturing process led to several pending patents and issued patents.

Since the founding of the company, Konarka has continued to refine the manufacturing process; increase the efficiency of its photovoltaic products; acquire key intellectual property from around the world; develop collaborations with leading research agencies, universities, and global energy companies; and develop products that provide a source of renewable power in a variety of form factors for commercial, industrial, government, and consumer applications around the world.

NTB: Did the Army eventually use the technology for soldier applications?

Dr. Brabec: The U.S. Army continues to utilize the technology in pilot programs to test its viability and use, and to further research and development.

NTB: Was Power Plastic® the result of that project?

Dr. Brabec: Power Plastic is a result of the project with the U.S. Army, as well as other research and development and pilot programs, including those with the U.S. Air Force, the National Science Foundation, the Defense Advanced Research Projects Agency (DARPA), the Department of Energy, and the Department of Commerce.

NTB: Is Power Plastic actually a new material, or is it made from existing materials?

Konarka’s Power Plastic photo-reactive material can be printed or coated onto flexible substratesusing roll-to-roll manufacturing, similar to how newspaper is printed on large rolls of paper. (Photo:David A. White)

Dr. Brabec: Konarka builds photovoltaic products using next-generation nanomaterials that are coated on rolls of plastic. The nanomaterials absorb sunlight and indoor light and convert them into electrical energy. These products can be integrated as the power-generation component for a variety of applications, and can be produced and used virtually anywhere.

The heart of the technology is a new way to make photovoltaic cells. Our photo-reactive materials can be printed or coated inexpensively onto flexible substrates using roll-to-roll manufacturing, similar to how newspaper is printed on large rolls of paper. The manufacturing process enables production to scale easily and results in significantly reduced costs over previous generations of solar cells.

NTB: Can Power Plastic be integrated into existing devices and systems?

Dr. Brabec: Yes, in a manner similar to how plastic is used today. We foresee Power Plastic used as both an attached source and an integrated source.

NTB: As an innovator in photovoltaic technologies at Siemens, what have been your major scientific research efforts at Konarka, and where do you see the next breakthrough in renewable power coming from?

Dr. Brabec: At Siemens, our effort was primarily focused on development, while at Konarka, our focus is on production. That is, the main difference is that we are now taking R&D work and turning it into something that can be produced with standard printing machines.

The next breakthrough in renewable power will come from producing Power Plastic material and making it competitive with traditional solar material, while continually improving performance.

NTB: Last year, Konarka was awarded funding from both the National Institute of Standards & Technology and the U.S. Department of Energy to research and develop photovoltaic cells and flexible solar modules for windows and other applications. How have these projects progressed, and how has this research contributed to the DOE’s goal of bringing down the cost of solar energy by 2015?

Dr. Russ Gaudiana, VP of Research: Making modules in a continuous roll-toroll process using well-known, highspeed coating and printing processes will lower solar energy costs significantly, relative to the current and anticipated competitive technologies. Support from these government agencies centers on development of advanced components and their application in processes that will lead to low-cost manufacturing of solar panels, windows, and portable battery chargers for laptops and handheld devices such as cameras and cell phones.

NTB: Earlier this year, you demonstrated the first inkjet printing of solar cells. What led to this breakthrough, and what are the far-reaching benefits? How will such a capability affect the cost, proliferation, and application of solar cells?

Dr. Brabec: Inkjet printing is an ideal tool for smaller-area, customized solar cells on various substrates with various patterns, as are typically required for indoor or portable applications. To do this, we had to understand the structure/ property relationship. That is, we had to understand how to treat it in order to give us the right properties of polymers. Once we learned that, we were able to formulate that particular type of printing and coating technology.

The energy required to produce our solar cells is negligible compared to what silicon providers need to do. Because of the low capital costs, energy use, and material costs, the overall production is less expensive. Additionally, when companies use a deposition technique, like many do, they are throwing material in the air and may lose some. However, in a direct print model, it’s more effective. Our waste and capital costs are minimal compared to traditional solar cells.

For more information on Konarka’s flexible solar cells, click here .