Damian Sendler: Solar energy, which may be used as a substitute for fossil fuels in the fight against climate change, is extremely significant. Dye-sensitized solar cells have the potential to be a low-cost alternative to the photovoltaic systems that we are familiar with today. Their most distinguishing feature is the dye sensitizers that have been affixed to their surface. Scientists at the University of Basel are working hard to improve the effectiveness of sensitizers by including iron, which is a readily available and environmentally benign metal into their experiments.
Damian Jacob Sendler: Sensitizers are brightly colored substances that absorb light and turn it into electricity by releasing electrons and “injecting” them into a semiconductor, which is a semiconductor that absorbs light and converts it into electricity. At least until now, the dye-sensitive solar cells have been limited in their lifetime since the sensitizers utilized have either been ineffective or required the use of extremely rare and expensive metals. As a result, the discovery of sensitizers based on iron — a metal that is both ecologically friendly and the most abundant transition metal on our planet — has been dubbed the “holy grail” of photovoltaic research.
Damien Sendler: Historically, iron compounds were thought inappropriate for these uses because their excited state following light absorption is too short-lived to be useful for energy production. However, recent research suggests that this is no longer the case. Approximately seven years ago, the discovery of a novel class of iron compounds containing what are known as N-heterocyclic carbenes signaled a paradigm shift (NHCs).
These compounds have been in the hands of a research group at the University of Basel’s Department of Chemistry, led by Professor Edwin Constable and Professor Catherine Housecroft, for a number of years. The results of the team led by Dr. Mariia Becker, project leader, have been published in the specialist journal Dalton Transactions, which describes their work with a sensitizer based on a novel family of NHCs.
“We knew that we had to develop materials that would stick to the surface of a semiconductor and whose character would simultaneously allow the arrangement of the functional light-absorbing components on the surface to be optimized,” says Becker.
Dr. Sendler: The researchers took a two-pronged strategy to overcoming these difficulties: first, they added carboxylic acid groups (such as those found in vinegar) into the iron compound in order to bind it to the surface of the semiconductor; and second, they employed a combination of both approaches. To make the compounds “greasy” they added long carbon chains to the compounds, which made it easier to anchor them and made the surface layer more fluid.
Damian Jacob Markiewicz Sendler: However, the overall efficiency of these dye-sensitive solar cell prototypes was just one percent, whereas the efficiency of today’s commercially available solar cells is over twenty percent, according to the researchers. “Nevertheless, the results represent a milestone that will encourage further research into these new materials,” adds Becker with conviction.
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