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Trace impurities are difficult to detect owing to their similarity to donor molecules in solar cells. The impurities can significantly influence photovoltaic properties
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Posted on 05/02/2012 1:59:44 PM PDT by neverdem
US chemists have shown that trace impurities - below the sensitivity of standard characterisation techniques - can halve the efficiency of bulk heterojunction (BHJ) solar cells. Their finding means that initially promising materials for device applications may have been written off prematurely owing to their low efficiencies.
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Trace impurities are difficult to detect owing to their similarity to donor molecules in solar cells. The impurities can significantly influence photovoltaic properties
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A team led by Guillermo Bazan and Alan Heeger from the University of California, Santa Barbara, noticed that organic semiconductors' effectiveness could vary from batch to batch. As the power conversion efficiencies of BHJ solar cells depend on the average molecular weight of the polymer, the team started by examining the definition of the structures and found that trace impurities in the donor of below 1% could halve device performance.
'We had no expectation of such a strong effect,' Bazan tells Chemistry World. 'Looking back, it makes sense based on the intense purity requirements of silicon solar cells, but it took us a long time to actually detect the impurities.' The standard characterisation techniques showed no difference between samples and it wasn't until the team examined mass spectroscopy results that they found the minute impurity: a methyl terminated by-product.
Igor Perepichka, who studies organic p-functional systems at Bangor University, UK, comments that it was surprising that a by-product with 'very similar energy levels and spectral characteristics has so drastic an effect on the performance'. Jianguo Mei from DuPont, China, raised concerns that the degree of purification might affect the commercialisation of the technology, pointing out that extra purification could negatively impact the cost effectiveness of such products.
Bazan sees it in a more positive light, highlighting the number of BHJ solar cells with unexpectedly low efficiencies and looks forward to seeing if this information could lead to BHJ solar cells outperforming their polymer counterparts in the future.
It's one thing after another!
We discovered this is 1980 when working on organic photoconductors for laser printers. We had to buy purified grain alcohol rather than reagent grade because of benzene contamination.
Late nights in the lab were lots of fun with all that grain alcohol around.
A hint: maybe they can revive with a shot of UV light.
UV light is the most destructive thing on the face of the Earth. To think any of these snake oil scams have a long life span is moronic
Solar cells ping!
They’ve yet to find a true ‘alternative’ energy source that runs 24/7 anyway, so ‘green’ energy is a big lie that actually increases the need for some of the least efficient generation modes as a backup for the green junk.
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...trace impurities - below the sensitivity of standard characterisation techniques - can halve the efficiency of bulk heterojunction (BHJ) solar cells.
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