Scientists from Imperial College London, the University of Surrey, the University of Nottingham, research institute UCL, Switzerland-based Fluxim and London South Bank University have designed a perovskite solar cell that integrates a ferrocene co-mediator interlayer at the interface between the spiro-OMeTAD hole transport layer (HTL) and the active perovskite material.
The team noted that the migration of lithium is critical in the degradation of spiro-OMeTAD-based devices, which is accelerated at higher temperatures, leading to the rapid degradation of the perovskite. The scientists described ferrocene as a sandwich structured material that is highly stable and can be used as a low-cost transition metal complex.
"Ferrocene has previously been incorporated into dye-sensitized solar cells (DSSCs) as a redox mediator, before being identified as an effective co-mediator when combined with inorganic redox shuttles enabling fast regeneration of oxidized sensitizers,” they specified. “When applied in organic photovoltaics (OPV) the addition of ferrocene has also been shown to improve carrier mobility and suppress recombination via the volatility of ferrocene and the ability to bridge between organic molecules, ordering the structure.”
“The application of metallocenes in perovskite solar cells is quickly becoming an exciting avenue for tackling the key challenges of perovskite solar cells including performance and stability,” researcher Thomas Webb claims.
The team found that the addition of ferrocene at the perovskite/spiro-OMeTAD interface rendered the lithium ions immobile, preventing them from migrating within the perovskite layer and thus significantly reducing their aggregation at the interface, where they can cause damage. This was achieved without compromising the perovskite cell efficiency. In addition, the diffusion of ferrocene into the HTL helped oxidize spiro-OMeTAD, improving its carrier transporting properties.
The solar cell developed with the proposed technique achieved a power conversion efficiency of 23.45%. It was also able to retain 70% of the initial efficiency after 1,250 hours stored at 60 C and 50% relative humidity.
In April 2022, a research team co-led by scientists from City University of Hong Kong (CityU) and Imperial College London developed highly efficient and stable perovskite solar cells with ferrocenes added to perovskite solar cells as an interface between the light-absorbing layer and the electron transporting layer.