News

23 November 2009

 

Search on for more abundant, efficient solar cell materials

California Institute of Technology (Caltech) and Dow Chemical Company have agreed to jointly develop lower-cost semiconductor materials for solar cells in a four-year, $4.2m effort to explore earth-abundant materials for solar-energy applications.

The research will initially focus on direct-bandgap semiconductor materials that incorporate elements that are less expensive and more commonly available than those used in today’s thin-film photovoltaic (PV) semiconductors. In particular, the researchers will investigate the use of earth-abundant elements to create new direct-bandgap PV structures.

Most solar cells today are constructed from silicon. Although an abundant low-cost material, silicon has an indirect energy bandgap. This means that, in absorbing photons to create a voltage, more energy is eventually lost as heat. More efficient cells can be made by using direct-bandgap materials. Unfortunately, such materials usually contain rare (and hence expensive) elements such as gallium (Ga) and indium (In).

To make up for its inadequacies, high-efficiency silicon solar cells need to use high-quality crystal substrates, which are relatively expensive compared with [thin-film’ solar technology using direct-bandgap materials such as cadmium telluride (CdTe) and copper indium diselenide (CIGS). Dow has previously developed CIGS for use in thin-film solar cells.

However, today’s direct-bandgap semiconductors contain elements too scarce (In, Ga, Te) to ultimately meet the demands of full-scale solar-energy technologies.

The Caltech/Dow project is led by applied physicist professor Harry Atwater and chemist professor Nate Lewis. Atwater’s research in PV has previously concentrated on achieving high cell efficiency in Si or GaAs by growth of very large-grain semiconductor films in low-temperature growth processes. Lewis has researched the photo-electrochemistry of semiconductor/liquid junctions as a means to store electrical energy produced by sunlight.

“Development of materials that are abundant in the earth’s crust will enable solar-energy technologies to ultimately scale to large volumes at low cost without concern about the materials’ availability,” says Atwater.

Picture: Nate Lewis (left) and Harry Atwater (right).

Dow recently announced its first building-integrated photovoltaic product, the POWERHOUSE Solar Shingle, which is designed to provide a product with lower cost, easier installation and an improved aesthetic for integration into rooftops with standard asphalt shingle materials. This product incorporates thin films of CIGS that can be incorporated into flexible products. However, the company remarks that some of the elements in CIGS and other thin-film semiconductors are in great demand, and are expensive and scarce. Dow is concerned that increased material costs could threaten the expanded adoption of PV as part of a comprehensive energy policy.

The new Dow/Caltech solar-research initiative is one of the company’s largest externally funded research agreements. A Dow Chemical Company Graduate Fellowship in Chemical Sciences and Engineering is also to be created at Caltech.

Search: Dow Chemical CdTe CIGS

Visit: www.dow.com

Visit: www. caltech.edu

The author Mike Cooke is a freelance technology journalist who has worked in the semiconductor and advanced technology sectors since 1997.