A UK research group has fabricated 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.
“We find that the ferrocene can capture lithium-ions via new applications of the novel properties of metallocenes, significantly improving the stability of leading perovskite solar cell devices,” the research’s corresponding author, Thomas Webb, told pv magazine. He further 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. “We believe that metallocenes are the next big thing in perovskite solar cells that will spark huge amounts of research.”
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.”
According to their findings, 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, we also identify the ability of ferrocene to act like an organic dopant, enhancing the oxidation of spiro-OMeTAD.”
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.
The academics described the cell in the paper A Multifaceted Ferrocene Interlayer for Highly Stable and Efficient Lithium Doped Spiro-OMeTAD-based Perovskite Solar Cells, published in Advanced Energy Systems. The research team includes scientists from Imperial College London, the University of Surrey, and London South Bank University.
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Source: pv magazine