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Posted: October 14, 2008

Researchers develop method to extend lifetime of organic solar cells

(Nanowerk News) IMEC's associated laboratory IMOMEC, located on the campus of the Hasselt University, developed a method to stabilize the nanomorphology of organic solar cells resulting in a lifetime improvement of at least a factor 10. With these stabilized solar cells, efficiencies were achieved comparable to state-of-the-art organic solar cells. This breakthrough paves the way to commercial organic solar cells with an operational lifetime of over 5 years and efficiencies of over 10%.
The efficiency and operation of organic solar cells strongly depends on the nanomorphology of the active layer, i.e. on a stable mix of organic compounds that can trap the light's energy and transport it to an electric contact. IMEC already reported such cells based on P3HT:PCBM with efficiencies near 5%.
But to date, the lifetime of these cells is far too short for commercial applications, for which 5 years is seen as a minimum. Under long term operation, all solar cells based on an intimate mixing of organic semiconductors deteriorate. This is due to segregation of the mixture whereby the compounds tend to separate into different phases and consequently reduce the efficient conversion of light into electricity.
IMEC has shown before that this phase segregation is related to the mobility of the organic polymer and that fixation of the nanomorphology of the polymers could result in a prolonged operational lifetime.
Comparison of degradation behavior of polymer/PCBM 1:1 solar cells based on a commercial conjugated polymer
Comparison of degradation behavior of polymer/PCBM 1:1 solar cells based on a commercial conjugated polymer (Rieke P3HT polymer - cell A) and on a novel conjugated polymer(cell B).
IMEC/IMOMEC has now introduced a new method and new conjugated polymers to stabilize the nanomorphology of the active layer making it far more robust to phase segregation under prolonged operation.
Experiments on bulk heterojunction organic solar cells based on this new material showed no degradation of the efficiency after more than 100 hours whereas reference cells degraded already after a few hours. This means that a lifetime improvement of at least a factor 10 can be obtained. And the cells achieved efficiencies near 4% which is comparable to state-of-the-art.
Transmission Electron Microscopy results for polymer/PCBM 1:1 active layers after degradation at 100 C for 2 hours
Transmission Electron Microscopy results for polymer/PCBM 1:1 active layers after degradation at 100°C for 2 hours, showing phase segregation for the Rieke P3HT polymer (left), but a stable morphology for the novel conjugated polymer (right).
Future research targets further refinement of the method by optimizing the chemical structures of the conjugated polymers.
About IMEC
IMEC is a world-leading independent research center in nanoelectronics and nanotechnology. IMEC vzw is headquartered in Leuven, Belgium, has a sister company in the Netherlands, IMEC-NL, offices in the US, China and Taiwan, and representatives in Japan. Its staff of more than 1600 people includes more than 500 industrial residents and guest researchers.
IMEC's More Moore research aims at semiconductor scaling towards sub-32nm nodes. With its More than Moore research, IMEC looks into technologies for nomadic embedded systems, wireless autonomous transducer solutions, biomedical electronics, photovoltaics, organic electronics and GaN power electronics.
IMEC's research bridges the gap between fundamental research at universities and technology development in industry. Its unique balance of processing and system know-how, intellectual property portfolio, state-of-the-art infrastructure and its strong network worldwide position IMEC as a key partner for shaping technologies for future systems.
Further information on IMEC can be found at www.imec.be.
Source: IMEC