The solar array atop the Vietnam Assembly and Test Factory in Ho Chi Minh City is the biggest operating solar facility in Vietnam. (Credit: Flickr @ Intel Free Press https://www.flickr.com/photos/intelfreepress/)Believe it or not we don’t totally understand how solar cells work, particularly organic thin-film photovoltaics. But scientists Canada, London and Cyprus have recently used lasers to shed some light into the process, which could help make more efficient solar panels tomorrow.
Earlier this week scientists at University of Montreal, the Science and Technology Facilities Council, Imperial College London and the University of Cyprus published a new report in Nature Communications explaining their findings. “Our findings are of key importance for a fundamental mechanistic understanding, with molecular detail, of all solar conversion systems,” said first author Françoise Provencher of the University of Montreal. “We have made great progress towards reaching a ‘holy grail’ that has been actively sought for several decades.”Diagram of how an organic PV molecule works.
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“We used femtosecond stimulated Raman spectroscopy,” explained Tony Parker of the Science and Technology Facilities Council’s Central Laser Facility. “Femtosecond stimulated Raman spectroscopy is an advanced ultrafast laser technique that provides details on how chemical bonds change during extremely fast chemical reactions. The laser provides information on the vibration of the molecules as they interact with the pulses of laser light.”
The information gained showed how the molecules in the solar cells were evolving. They found two main things: rapid molecular rearrangement and very small amounts of molecular relaxation and reorganization. The rearrangement or response is incredibly fast—300 femtoseconds. The researchers explained that in perspective a femtosecond is to a second as a second is to 3.7 million years.
“In these and other devices, the absorption of light fuels the formation of an electron and a positive charged species. To ultimately provide electricity, these two attractive species must separate and the electron must move away. If the electron is not able to move away fast enough then the positive and negative charges simple recombine and effectively nothing changes. The overall efficiency of solar devices compares how much recombines and how much separates,” explained Sophia Hayes of the University of Cyprus, last author of the study.
“Our findings open avenues for future research into understanding the differences between material systems that actually produce efficient solar cells and systems that should be as efficient but in fact do not perform as well. A greater understanding of what works and what doesn’t will obviously enable better solar panels to be designed in the future,” said the University of Montreal’s Carlos Silva, senior author of the study.
This article was originally posted on SolarReviews by Chris Meehan.
Provencher, F., Bérubé, N., Parker, A., Greetham, G., Towrie, M., Hellmann, C., Côté, M., Stingelin, N., Silva, C., & Hayes, S. (2014). Direct observation of ultrafast long-range charge separation at polymer–fullerene heterojunctions Nature Communications, 5 DOI: 10.1038/ncomms5288
