New Probe to Enable PV Cell Improvement
Researchers at South Dakota State University are looking to probe various defects and their influence on the overall efficiency of solar cells. A first-of-its-kind scanning probe microscope they are working on is expected to play an important role in improving solar cell and LED efficiency.
Alexander E. Braun, Senior Editor -- PV Society, 1/5/2010
Professor Venkatesware Bommisetty, of the Department of Electrical Engineering and Computer Science at South Dakota State University (SDSU, Brookings, S.D.), is working to build a first-of-its-kind microscope that he expects will play an important role in improving solar cell and LED efficiencies.
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Professor Venkateswara Bommisetty is using an NSF grant to build a unique microscope with which to study and improve photovoltaic efficiencies. (Source: SDSU) |
The work that Bommisetty and his team are carrying out is specifically aimed at probing various defects, different structures at nanoscale levels, and their influence on the overall efficiency of solar cells. Bommisetty's research efforts have been partly focused on developing better technologies to make such measurements at the nanoscale level. "Here at the university, we're doing research on all kinds of solar cells: silicon, organic and hybrids," he said. "Normally, the efficiencies we are able to obtain out of these cells are lower than what we should really be able to get. Most researchers — including us — do not know what the reason for this is, and where and at what scale these efficiency losses are occurring." This research into photoactivated processes is being funded by a $456,000 National Science Foundation grant, with SDSU and its Department of Electrical Engineering and Computer Science supplying an additional $200,000.
The SDSU scientist and his team are in the process of building what he describes as a photoactivated scanning probe microscope tool that, according to him, will be significantly better than any other existing scanning probe microscope. Although Bommisetty cannot currently divulge too many details about his work, he indicated that the microscope will use certain types of illumination schemes, as well as an innovative lever detection system. "The mechanism varies from a typical commercial scanning probe," he said. "When you scan a solar cell, there is some light inside as well as in scanning probes. This is one of the reasons why people have difficulties in using a scanning probe to probe inside materials."
According to Bommisetty, the microscope is expected to simultaneously measure efficiency-limiting factors by identifying defects, their structure and locations in a wide variety of solar cells that existing microscopes are not able to do. The scanning probe microscopy tool will be designed to measure simultaneously different variables — a key advance in such technology, because if only one variable is measured at a time, it is not possible to know whether the act of measurement itself is modifying other variables. "If we measure them all at the same time, we can determine the exact problem and can effectively develop methods to address the problem," he said.
Bommisetty stated that at SDSU work is proceeding on all three types of solar cells: inorganic solar cells based on materials such as silicon, organic solar cells that use carbon-based polymers, and hybrid solar cells that combine different technologies. "The faculty members at SDSU are working on all these three types. In each of the respective solar cells, the challenges are different," he said. "We know that all these technologies can be far more efficient than what they are today. The problem is we don't know which factors limit the efficiencies of these solar cells. This microscope is specifically designed to identify defects that limit solar cell efficiency." Bommisetty added that since the tool can be used to study any material where there are light/energy conversion mechanisms such as are found in optoelectronic devices, it should also be particularly useful in the study and improvement of LEDs.
SDSU already is acquiring components, and assembly of the tool is scheduled to begin this year. One version of the microscope will go into the molecular electronics bay of a new $1.25M SDSU cleanroom, planned for construction in 2010, where scientists can use it to test new solar cells.
