Progress Of Iron Enriched Dye Sensitized Solar Cells

University of Basel researchers continue to improve the performance dye sensitized solar cells with sensitizers using iron – a commonly available and environmentally friendly metal.

Solar energy plays an important role in the fight against climate change as a substitute for fossil fuels. Dye-sensitized solar cells promise to be a low-cost supplement to the photovoltaic systems we know today. Their key feature is the dye sensitizers attached to their surface.

Sensitizers are intensely colored compounds that absorb light and convert its energy into electricity by releasing electrons and “injecting” them into the semiconductor. So far, the sensitizers used in the dye-sensitized solar cells have either been relatively short-lived or demanded the use of very rare and expensive metals. The holy grail of photovoltaic research is therefore the development of sensitizers using iron – a metal that is both environmentally friendly and the most abundant transition metal on our planet.

For many years, experts considered iron compounds to be unsuitable for these applications because their excited state following light absorption is too short-lived to be of use for energy production. This changed around seven years ago with the discovery of a new class of iron compounds with what are known as N-heterocyclic carbenes (NHCs).

The research group headed by Professor Edwin Constable and Professor Catherine Housecroft at the University of Basel’s Department of Chemistry has been working with these compounds for a number of years. The team led by project leader Dr. Mariia Becker has now reported on their results with a sensitizer based on a new family of NHCs in the specialist journal Dalton Transactions.

Dr. Becker explained, “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.”

The researchers used a two-pronged approach to these challenges: first, they incorporated carboxylic acid groups (as found in vinegar) into the iron compound in order to bind it to the semiconductor’s surface. Secondly, they made the compounds “greasy” by adding long carbon chains that made the surface layer more fluid and easier to anchor.

These dye-sensitized solar cell prototypes only achieved overall efficiency of 1 percent, while today’s midstream commercially available solar cells reach around 20 percent efficiency. “Nevertheless, the results represent a milestone that will encourage further research into these new materials,” said Becker with conviction.

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For solar cells to become a true mass market product without government incentives and subsidies whose cost is borne by everyone only to benefit a few – this kind of research is critical and deserves support and attention. So far solar is not truly practical. When it really is, it will be the normal choice for everyone.

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