Increasing Efficiencies For Thin Film Solar Cells: Different Approaches Researched By The US DOE

By Dr. Harry Zervos, IDTechEx

Recently, researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) announced that they have moved closer to creating a thin-film solar cell that can compete with the efficiency of the more common silicon-based solar cell. The Copper Indium Gallium Diselenide(CIGS) thin-film solar cell recently reached 19.9% efficiency in testing at the lab, setting a new world record, as the NREL revealed on March 24 2008.

This is still far from the highest efficiency achieved in July 2007 by a consortium of researchers led by the University of Delaware (42.8% using a novel technology that adds multiple innovations to a very high-performance crystalline silicon solar cell platform) but of course there are big differences in the manufacturing costs of these two technologies as well as the potential fields of application for them.

The following table by the U.S. Department of Energy gives an idea of thin film market share by technology and cost of modules.

Table 1: thin film market share module cost by technology

The above table indicates the dominance of amorphous silicon and cadmium telluride (CdTe) technologies when compared to the current market size of CIGS solar cells. There is a lot of vibrant activity in the CIGS field though, with a number of companies finding themselves in different stages of implementation, ranging from raising funds to building power plants or producing modules (Nanosolar is printing modules in their facilities in the USA and in Germany). Together with companies such as Global Solar, Daystar, Miasolé, SoloPower and Ascent Solar, it is obvious that key CIGS manufacturers are becoming increasingly competitive and in the next few years will be enjoying a much larger share of the thin film market. Announcements such as the one made from NREL (achieving the highest efficiency out of all thin film technologies) increases the support of CIGS and gives confidence to manufacturers that their improved products and their low manufacturing costs will attract the attention of more and more customers.

Improvements in CIGS modules do not only come in increased efficiencies of the modules but also in other forms. SoloPower and Ascent Solar are announcing that their modules will be flexible rather than on glass (flexible metal foil for SoloPower, high temperature plastic substrate for Ascent Solar) thus increasing the versatility and variety of potential applications.

The NREL is facilitating adoption and improved performance of new technologies in other ways as well. Through the U.S. Department of Energy's (DOE) Technology Commercialization Development Fund (TCDF) Program, NREL can expand its collaborative efforts between researchers and companies to develop commercial products based on NREL innovations. NREL has received $4 million from the TCDF for the fiscal year 2008. It's one of three DOE laboratories, along with Oak Ridge National Laboratory, which received $2.5 million, and Sandia National Laboratories, which received $700,000.

Optimization of solar cell technologies is tackled in a different way at the Oak Ridge National Laboratory (ORNL). ­The ORNL pulse thermal processing (PTP) technique is a revolutionary enabling technology for functionalizing nano-materials due to its ability to control diffusion at the nanometer scale. It utilizes a unique high density plasma arc lamp, which is the most powerful radiant arc lamp in the world. ORNL has been partnering with Mattson Technology, Inc., the manufacturer of the plasma arc technology, for several years to further enhance the technologies capabilities. Power densities on the order of 20,000 W/cm² can be achieved over broad areas (currently up to 1,000 cm²) and can be pulsed in 1 millisecond. According to Dr. Ron Ott of the ORNL "The inherent characteristics of this technology (high heating rates, short processing times and larger processing areas) enable unique thermal annealing capabilities that can potentially revolutionize PV material systems."

The combination of optimizing material systems as well as optimizing processing techniques for these materials gives multiple pathways towards achieving increase in performance from solar cells that can eventually lead to grid parity in terms of cost and efficiency, which seems to be one of the biggest challenges that solar technologies are currently facing.

Speakers from the NREL as well as the ORNL (Dr. Arthur frank and Dr. Ron Ott respectively) are going to be presenting the advances in the research and design efforts in these leading institutes at the Photovoltaics "Beyond Conventional Silicon" Conference in Denver, Colorado on June 17-18, 2008. IDTechEx is hosting the premier event with speakers from both the academic world and industry from across the globe, giving a comprehensive overview of the current situation in the world of ground-breaking solar cell technologies.

For further information on the conference, the agenda and related events, please visit www.idtechex.com/pvUSA

SOURCE: IDTechEx Inc.