Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Ames Laboratory Researchers Hope to "Sunproof" Solar Cells

09.04.2003


Computer Simulations Provide Insight On Light Degradation Effect in Solar Cells



Scientists at the U.S. Department of Energy’s Ames Laboratory and Iowa State University’s Microelectronics Research Center may have solved a mystery that has plagued the research community for more than 20 years: Why do solar cells degrade in sunlight? Finding the answer to that question is essential to the advancement of solar cell research and the ability to produce lower-cost electricity from sunlight.

"The basic problem is that when you put solar cells in sunlight, the efficiency starts to decrease by as much as 15 percent to 20 percent over a period of several days," said Rana Biswas, a physicist at Ames Laboratory and the MRC. "Obviously, that’s not good."


Solar cells made from hydrogenated amorphous silicon, a noncrystalline form of silicon, absorb light far more effectively than traditional crystalline silicon solar cells. "Instead of a thick, 20-micron crystalline silicon film, you can just deal with a very thin, half-micron amorphous silicon film," said Biswas. "These cells are more cost-effective as they involve much less material and processing time - driving forces for industry. However, although amorphous silicon absorbs light very efficiently, it suffers from this degradation effect - that’s the bad news."

Biswas and his co-workers have been studying the troublesome degradation effect, also known as the Staebler-Wronski effect, for the past few years. The effort includes investigations into the atomic origins of the S-W effect and the subsequent exploration of possible new solar cell materials through computer molecular dynamics simulations.

Biswas explained that exposure to light can cause changes in hydrogenated amorphous silicon, resulting in defects known as metastable dangling bonds - bonds that can go away only when heated to a high temperature. Dangling bonds are missing a neighbor to which they can bond. To remedy the situation, they will "capture" electrons, reducing the electricity that light can produce and decreasing solar cell efficiencies. "The question," Biswas said, "is how does light create the dangling bonds?"

The answer has long been a mystery, but now Biswas and his co-workers, Bicai Pan and Yiying Ye, are helping resolve many puzzling aspects of the problem with their three-step atomistic rebonding model. The model is based on rearrangements of silicon and hydrogen atoms in the hydrogenated amorphous silicon material. In the first step, sunlight creates excited electrons and holes (vacant electron energy states) in the material. When the electrons recombine, they pair up with holes on the weak silicon bonds. The recombination energy causes the weak silicon bonds to break, creating silicon dangling bond-floating bond pairs. During the second step, the floating bonds break away from the dangling bonds and move freely throughout the material. This occurs when the extra floating bond from one silicon atom moves to a neighboring silicon atom. The third step reveals that the short-lived floating bonds disappear. Some recombine with the silicon dangling bonds, which results in no material defects. Others "hop" away from the dangling bonds and are annihilated when hydrogen atoms in the network move into the floating bond sites.

Biswas’ three-step rebonding model shows that defect creation in hydrogenated amorphous silicon solar cells is initially driven by the breaking of weak silicon bonds followed by the rebonding of both silicon and hydrogen sites in the material. The research represents a significant achievement in understanding the atomic origins of the light-induced degradation effect in hydrogenated amorphous silicon and so provides a vantage point for eliminating this effect in the development of new solar cell materials - a task on which Biswas is now focusing his efforts.

To improve the efficiency and reliability of solar cells, Biswas and his co-workers are investigating mixed-phase solar cell materials - a mixture of clusters of nanocrystalline silicon embedded in an amorphous matrix. "One of the most promising developments has been the success of hydrogen-diluted materials grown at the edge of crystallinity - the phase boundary between microcrystalline and amorphous film growth," said Biswas. "These materials and solar cells made from them have a much greater stability to light-induced degradation than traditional amorphous material."

By developing molecular dynamics computer simulations, Biswas hopes to learn more about this mixed-phase material at the atomic level and discover what aspect of the mixture is responsible for the improved material properties. His research efforts may even extend to manipulating the nanoscale structure of the material, allowing the design and creation of improved materials.

The research is funded by DOE’s Energy Efficiency and Renewable Energy Office through the National Renewable Energy Laboratory and is administered by the Institute for Physical Research and Technology, a network of research and technology-transfer centers at ISU. The American Chemical Society provided start-up funds. Ames Laboratory is operated for the DOE by ISU. The Lab conducts research into various areas of national concern, including energy resources, high-speed computer design, environmental cleanup and restoration, and the synthesis and study of new materials.

Rana Biswas | DOE/Ames Laboratory
Further information:
http://www.external.ameslab.gov/News/release/2003rel/solar.html
http://www.external.ameslab.gov/

More articles from Power and Electrical Engineering:

nachricht A big nano boost for solar cells
18.01.2017 | Kyoto University and Osaka Gas effort doubles current efficiencies

nachricht Multiregional brain on a chip
16.01.2017 | Harvard John A. Paulson School of Engineering and Applied Sciences

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

A big nano boost for solar cells

18.01.2017 | Power and Electrical Engineering

Glass's off-kilter harmonies

18.01.2017 | Materials Sciences

Toward a 'smart' patch that automatically delivers insulin when needed

18.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>