New, cheaper and easier-to-manufacture solar cell devices may soon hit the market thanks to materials made at Imperial College London.
Traditional solar cells are made from silicon, which has good efficiency and stability, but is relatively expensive to manufacture and can only be made into rigid panels.
Perovskite solar cells offer an interesting alternative: they can be printed from inks, which makes them inexpensive, highly efficient, thin, light and flexible. However, they have lagged behind silicon solar cells in efficiency and, more importantly, stability, as they break down under normal environmental conditions.
New materials containing metals called ferrocenes could help solve these problems. Researchers at the City University of Hong Kong (CityU) have added Imperial-made ferrocenes to perovskite solar cells, dramatically improving their efficiency and stability.
Silicon cells are efficient but expensive, and we urgently need new solar power devices to accelerate the transition to renewable energy. Stable and efficient perovskite cells could eventually enable solar power to be used in more applications, from powering the developing world to charging a new generation of portable devices.
Our collaboration with colleagues from Hong Kong was a nice coincidence, which happened after I gave a lecture on new ferrocene compounds and met Dr. Zonglong Zhu from CityU, who asked me to send him some samples. Within months, the CityU team told us the results were exciting and asked us to send more samples, beginning a research program that led to more efficient and stable perovskite devices.
Nicholas Long, Department of Chemistry at Imperial.
The power of ferrocenes.
Perovskite forms the “light-collecting” layer of solar cell devices. However, these devices have been less efficient at converting solar energy into electricity than silicon-based solar cells, mainly because the electrons are less “mobile”, i.e. less able to move the crop to electricity conversion layers.
Ferrocenes are compounds whose center is iron, surrounded by rings of carbon. The unique structure of ferrocene was first recognized by Imperial Nobel Prize winner Professor Geoffrey Wilkinson in 1952, and ferrocenes continue to be studied around the world for their unique properties.
One of the properties conferred by their structure is an excellent electron richness, which in this case allows electrons to move more easily from the perovskite layer to the following ones, improving the efficiency of the conversion of solar energy into electricity.
Tests conducted by the CityU team and in commercial labs show that the efficiency of perovskite devices with an added ferrocene layer can be as high as 25%, approaching the efficiency of traditional silicon cells.
Two birds with one stone.
But that’s not the only problem ferrocene-based materials solve.
The Imperial team experimented with the attachment of different chemical groups to the carbon rings of ferrocene, and after sending various versions of these, made by PhD student Stephanie Sheppard, to the Hong Kong team, the collaborators discovered a version that significantly improves the binding. layers of perovskite to the rest of the device.
This extra holding power improved the stability of the devices, meaning they held more than 98% of its initial efficiency after continuous operation at full power for 1500 hours. The efficiency and stability achieved by adding a layer of ferrocene bring these perovskite devices closer to current international standards for traditional silicon cells.
We are the first team to raise the inverted perovskite solar cell to a record 25% efficiency and pass the stability test set by the International Electrotechnical Commission.
Dr. Zonglong Zhu, Principal Investigator.
The team has patented their design and hope to obtain a license to commercialize their perovskite devices. In the meantime, they are experimenting with different designs of ferrocene to further improve the performance and stability of the devices.
More information: www.science.org (English text).