New Material Developed at Imperial Could Set the Stage for Availability of Solar Cells in the Market

Thanks tothe materials fabricated at Imperial College London (ICL), new solar cell devices that are simpler and more affordable to make could soon be commercially available.

Conventional solar cells are composed of silicon, possessing good stability and efficiency. However, it is comparatively costly to make and can only be manufactured into hard panels.

An interesting alternative has been provided by the perovskite solar cells. They can be printed from inks, making them thin, affordable, lightweight and flexible, and highly efficient. But they have trailed behind silicon solar cells in efficiency and, crucially, stability, breaking down under normal environmental conditions.

Stable and efficient perovskite cells could ultimately allow solar energy to be used in more applications.

Nicholas Long, Professor, Imperial College London

These issues can be resolved with the help of new metal-containing materials known as ferrocenes. Scientists from the City University of Hong Kong (CityU) have added Imperial-made ferrocenes into perovskite solar cells, thereby enormously improving their stability and efficiency. The study outcomes are reported recently in the Science journal.

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.

Nicholas Long, Study Co-Lead Author, Department of Chemistry, Imperial College London

Long continued, “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 program that has resulted in perovskite devices that are both more efficient and more stable,” added Long.

The Power of Ferrocenes

The so-called “light-harvesting” layer of solar cell devices has been developed by the perovskite. But these devices have proven to be less efficient at converting solar energy into electricity compared to silicon-based solar cells.

This is mainly because the electrons tend to be less “mobile,” implying that they are less able to shift from the harvesting layer to the electricity conversion layers.

Ferrocenes are compounds consisting of iron at their center and surrounded by sandwiching rings of carbon. Initially, the special structure of ferrocene was identified by Imperial’s own Nobel Prize-winner Professor Geoffrey Wilkinson in 1952, and ferrocenes are still being researched throughout the world at present for their unique properties.

Outstanding electron richness is one such property that enables electrons to shift more easily from the perovskite layer to the following layers, thereby enhancing the efficiency of converting solar energy to electricity.

Several tests performed by the research team from CityU and in commercial laboratories have shown that the efficiency of perovskite devices with an added ferrocene layer could reach nearly 25% - approaching the efficiency of conventional silicon cells.

Two Birds with One Stone

However, this is not the only issue that has been solved by the ferrocene-based materials. The research group at Imperial has been trying to experiment with fixing various chemical groups to the carbon rings of ferrocene.

Also, after sending the Hong Kong team numerous versions of these, made by Ph.D. student Stephanie Sheppard, the collaborators found a version that considerably enhances the fixation of the perovskite layers to the remaining parts of the device.

The stability of the devices was enhanced by this added attachment power, thereby implying that they retained over 98% of their initial efficiency following continuous operation at utmost power for 1,500 hours.

The stability and efficiency gained as a result of the addition of a ferrocene layer brings these perovskite devices close to current international standards for conventional silicon cells.

Dr. Zonglong Zhu, lead researcher from CityU stated, “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.”

Their design has been patented by the team and they are also looking to license it, ultimately making their perovskite devices commercially available. At the same time, they are experimenting with various ferrocene designs to additionally enhance the stability and performance of the devices.

Journal Reference:

Li, Z., et al. (2022) Organometallic-functionalized interfaces for highly efficient inverted perovskite solar cells. Science. doi.org/10.1126/science.abm8566