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Traditionally, solar cells have been made from silicon, which is efficient and stable but can only be produced in stiff panels. Perovskite solar cells have been an area of interest in recent years – these can be printed from inks, making them thin, light and flexible, as well as cheaper. But they've failed to take over from silicon in part because they are not as efficient, and they break down too easily under normal environmental conditions.
Now, researchers from City University of Hong Kong (CityU) have incorporated a new type of material called ferrocenes, made at Imperial, into perovskite solar cells, improving their efficiency and stability. Ferrocenes are compounds with iron in the centre, surrounded by sandwiching rings of carbon, which gives them unique properties.
They have, for instance, excellent electron richness, which allows electrons to move more easily from the perovskite layer to subsequent layers, improving the efficiency of converting solar energy to electricity.
Research published this week in the journal Science by the CityU team reports that the efficiency of perovskite cells with added ferrocene can reach 25 per cent, close to that of traditional silicon cells.
Co-lead author Professor Nicholas Long, from the Department of Chemistry at Imperial, said: “Silicon cells are efficient but expensive, and we urgently need new solar energy devices to accelerate the transition to renewable energy. Stable and efficient perovskite cells could ultimately allow solar energy to be used in more applications – from powering the developing world to charging a new generation of wearable devices.
“Our collaboration with colleagues in Hong Kong was beautifully serendipitous, arising after I gave a talk about new ferrocene compounds and met Dr Zonglong Zhu from CityU, who asked me to send over some samples. Within a few months, the CityU team told us the results were exciting, and asked us to send more samples, beginning a research programme that has resulted in perovskite devices that are both more efficient and more stable.”
The researchers were also able to use ferrocenes to improve the stability of perovskite cells by experimenting with attaching different chemical groups to the carbon rings of ferrocene.
This added attachment power improved the stability of the devices, meaning they maintained more than 98% of their initial efficiency after continuously operating at maximum power for 1,500 hours. The efficiency and stability gained thanks to the addition of a ferrocene layer brings these perovskite devices close to current international standards for traditional silicon cells.
Lead researcher Dr Zonglong Zhu from CityU said: “We are the first team to successfully boost the inverted perovskite solar cell to a record-high efficiency of 25% and pass the stability test set by the International Electrotechnical Commission.”
The team have patented their design and hope to license it, eventually bringing their perovskite devices to the market.
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