The University of Arizona

Industry and Reseach Collaborate to Improve Solar Cell Efficiency

By Rebecca Ruiz-McGill, University Communications | November 13, 2009

Research meets industry as two Tucson companies and UA professor Ray Kostuk have been awarded a three-year grant to investigate holographic optical collectors in solar technologies.

Professor Ray Kostuk
Professor Ray Kostuk
Front left, Deming Zhang and Jose Castro are apply theory to application as they work on improving solar cell efficiency with holograms in professor Kostuk's lab.
Front left, Deming Zhang and Jose Castro are apply theory to application as they work on improving solar cell efficiency with holograms in professor Kostuk's lab.

Professor Raymond K. Kostuk and two Tucson companies have secured a $330,000 three-year grant from the National Science Foundation to investigate methods to optimize solar energy efficiency that blend low-cost holographic optical collectors with thin-film solar cell technologies. 

Solar energy is the most abundant form of renewable energy but the greatest issue with harnessing this resource is the cost of the conversion process, said Kostuk, a professor of electrical and computer engineering.

Photovoltaic energy conversion is one of the most viable ways of harnessing solar energy. However the cost of this process remains high in comparison with fossil fuel energy sources. This point was made clear by the National Academy of Engineering, which has cited "making solar energy economical'' as its No. 1 "grand challenge" for the technical community to solve.

Current commercial solar cells are most often made from silicon and typically convert sunlight into electricity with an efficiency of only 15 to 20 percent. This greatly impacts the overall cost and land area required to generate adequate levels of electricity, Kostuk said.

According to the U.S. Department of Energy, given their manufacturing costs, modules using today's cells produce electricity at a cost roughly three to six times higher than current prices for fossil fuel generation.

"The chance to direct and work on a project like this is a dream come true. I consider myself quite fortunate to be able to do something that is of such importance and value to society," Kostuk said of the grant. 

Kostuk, his team of graduate students, and local industry leaders at Prism Solar Technologies and Global Solar Energy will work to improve the efficiency of thin-film photovoltaic cells with the use of holographic-collection and light-trapping techniques. This approach ultimately will lower the cost of the resultant modules.

"The proposed work will advance the design of holographic nonimaging optics. The individual aspects of different components have been studied in the past but evaluation of their utility for the purpose of optimizing the electrical performance of a thin film PV cell is a new and important contribution," Kostuk said.

The project is funded by grant given by the NSF's Grant Opportunities for Academic Liaison with Industry, or GOALI, program, which aims to synergize university-industry partnerships by making project funds or fellowships/traineeships available to support industry-university linkages.

"The grant is a collaborative effort between university and industry. Together, we will be addressing one of the most important aspects of renewable energy research, which is to try and reduce the cost of photovoltaic energy sources," Kostuk explained.

Prism Solar Technologies designs and manufactures products that improve the efficiency of solar energy collection. Prism uses holographic optics in the form of an optical film that can be used in combination with any photovoltaic cell technology. The company's core technology is based on holographic optics that selects the optimum spectrum of sunlight that will allow for "cooler" solar cell operation while creating more kilowatt hours of energy per day and per year.

Global Solar Energy manufactures thin-film solar cells and is engaged in thin-film photovoltaic cell research and development. Global Solar Energy produces thin-film photovoltaic material using a patented CIGS (Copper Indium Gallium diSelenide) process. The company joins the grant with an interest in determining how holographic optics may add significant design capability to the cell structures they currently manufacture.

At present, Kostuk said, there are two approaches being investigated to reduce the cost of photovoltaic systems.

The first is to use concentrators that gather light with a large optical collector and to direct it to a smaller high efficiency photovoltaic cell. This method lowers cost by replacing expensive photovoltaic material with a less expensive optical collector.

The second approach involves the development of thin-film cells, manufactured by low-cost methods, that reduce the amount of expensive photovoltaic conversion material and thereby reduces the cost of the new system. However, thin-film cells suffer from lower efficiency than silicon cells.

Kostuk's team will focus on using low levels of optical concentration to optimize the efficiency of CIGS thin-film cells, minimizing optical tracking requirements, and providing light-trapping mechanisms to further enhance the electrical conversion efficiency of the thin-film cell. To accomplish these aims, the team will use multiple optical functions that can be incorporated into low-cost holographic optical components.

"The primary goal of the proposed work is to take a new approach to photovoltaic system design that incorporates low-cost holographic optical elements in planar optic configurations with thin-film PV cells. The fundamental research benefit of this work will be to investigate methods of advancing the performance of the thin-film PV cells by optimizing their response to selected solar spectral bands, concentration ratios, aperture segmentation, and light trapping through co-design of the electrical properties of thin-film cells with holographic optics," Kostuk added.

The UA-industry team will work together in a variety of ways.

The basic and also nonproprietary geometrical and material structures for the CIGS photovoltaic cells has been provided by Global Solar Energy so that Kostuk's team at the UA can model the absorption properties with different angular and spectral illumination conditions.

Experimental characterization of the concentration properties of CIGS photovoltaic cells will be conducted at the UA and compared with data obtained at Prism Solar Technologies and Global Solar Energy. Concentration and spectral enhancement data will then be used to design holographic collector and light-trapping elements.

The development of a design methodology for modeling holographic elements in planar optic configurations will be conducted by the Kostuk group at UA.

Kostuk also will host technical researchers from the companies to instruct them on how to use holographic design and will provide photovoltaic interaction models and energy collection analysis tools developed at the UA.

The grant will fund the research for three years and will provide Kostuk's graduate students (current and new) with an opportunity to work with solar energy professionals.

"We anticipate new opportunities for intern students at both companies as a result of this collaboration," Kostuk said.

Two of Kostuk's graduate students specifically chose the UA because of its strengths in solar energy research and have the opportunity to move theory to application.

Jose Castro, a postdoctoral research professor in electrical engineering, returned to the UA from industry to continue pursuing research after seeing the potential that holograms have both in solar applications and in medical imaging.

"In industry, they know how to manufacture. They have the process but they don't necessarily have the time to try different approaches – to create different models or designs. When you work with the University, you have the opportunity to try something new; you have the opportunity for innovation. We can complement industry on the research side and create new models and designs and see what works best."

"It is a versatile technology which can be used in a variety of applications," said Deming Zhang, a doctoral student in electrical engineering who also works in Kostuk's lab. "There is a lot of research to do in the area of holography. The more students working on this area, the better results we can have. With this grant, there will be more collaboration with industry, which is very helpful for research."