The cells in question are a joint venture between Imperial and City University of Hong Kong (CityU).
“Our collaboration with was beautifully serendipitous, arising after I gave a talk about new ferrocene compounds and met Zonglong Zhu from CityU, who asked me to send over some samples,” said Imperial chemist Professor Nicholas Long, “Within a few months, the CityU team told us the results were exciting, and asked us to send more samples, beginning a research program that has resulted in perovskite devices that are both more efficient and more stable.”
Ferrocenes are compounds with iron at their centre, surrounded by sandwiching rings of carbon.
They are electron-rich, improving electron mobility between the energy-harvesting perovskite layer and subsequent layers, boosting conversion efficiency.
Following good initial results, Imperial attached chemical groups to the carbon rings to create designer ferrocenes particularly for perovskite cells, with one particular version improving the bond between perovskite layers and the rest of the device, increasing device stability, even in hot damp environments.
“This added attachment power maintained more than 98% of initial efficiency after continuously operating at maximum power for 1,500hours”, according to Imperial “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.”
“We are the first team to successfully boost the inverted perovskite solar cell to 25% efficiency and pass the stability test set by the International Electrotechnical Commission,” added CityU’s Zhu.
The special ferrocene is ferrocenyl-bis-thiophene-2-carboxylate (FcTc2), and the work applies to inverted (p-i-n) structure perovskite solar cells (see diagram) that already tend to live longer than more conventional n-i-p types, at the expense of lower power efficiency.
The technology has been patented and will be available for licencing. It is described in ‘Organometallic-functionalized interfaces for highly efficient inverted perovskite solar cells‘ published in Science.