Innovative Technology Offers Big Performance Boost to Perovskite–Silicon Tandem Solar Cells

Significant performance gains in perovskite silicon tandem solar cells (like the one pictured here) can be achieved by adding a magnesium fluoride interlayer. Photo credits: © 2022 KAUST; Erkan Aydin

An additional metal fluoride layer enables charge separation and increases the performance of perovskite silicon tandem solar cells.

Inserting a metal fluoride layer into multilayer perovskite silicon tandem solar cells can stop charge recombination and improve performance, researchers at King Abdullah University of Science & Technology (KAUST) have found.

Tandem solar cells, which combine perovskite and silicon-based subcells in one device, are said to capture sunlight and convert it into electricity better than their traditional single-junction silicon competitors. And probably at a lower cost. However, when sunlight strikes the perovskite subcell, the resulting pairs of electrons and positively charged holes tend to recombine at the interface between the perovskite and the electron transport layer. In addition, a mismatch between the energy levels at this interface impedes electron separation within the cell. These issues combine to reduce the open circuit voltage, or maximum operating voltage, of the tandem cells, limiting device performance.

By adding a layer of lithium fluoride between the perovskite and the electron transport layer, which typically contains the electron acceptor fullerene (C60), these performance concerns can be partially resolved. However, the devices become unstable as lithium salts readily liquify and diffuse through surfaces. Lead author Jiang Liu, a postdoc in Stefaan De Wolf’s group, explains: “None of the devices passed the International Electrotechnical Commission’s standard test protocols, leading us to create an alternative.”

Liu, De Wolf and colleagues systematically investigated the potential of other metal fluorides such as magnesium fluoride as interlayer materials on perovskite/C60 Interface of tandem cells. They thermally evaporated the metal fluorides on the perovskite layer to form an ultra-thin, uniform film of controlled thickness before adding C60 and Top Contact components. The interlayers are also highly transparent and stable, which meets the requirements of inverted pin solar cells.

The magnesium fluoride interlayer effectively promoted electron extraction from the perovskite active layer while C was displaced60 from the perovskite surface. This reduces charge recombination at the interface. It also improved charge transport across the subcell.

The resulting tandem solar cell achieved a 50 millivolt increase in its open circuit voltage and a certified stabilized power conversion efficiency of 29.3 percent — one of the highest efficiencies for perovskite silicon tandem cells, Liu says.

“Considering that the best efficiency for mainstream single-junction cells based on crystalline silicon is 26.7 percent, this innovative technology could bring significant performance gains without increasing manufacturing costs,” says Liu.

To further explore the applicability of this technology, the research team is developing scalable methods to fabricate perovskite silicon tandem cells on an industrial scale with areas greater than 200 square centimeters (31 square inches). “We are also developing multiple strategies to obtain highly stable tandem devices that pass critical industrial stability protocols,” says Liu.

Reference: “Efficient and stable perovskite silicon tandem solar cells by contact displacement by MgFx” by Jiang Liu, Michele De Bastiani, Erkan Aydin, George T. Harrison, Yajun Gao, Rakesh R. Pradhan, Mathan K. Eswaran, Mukunda Mandal, Wenbo Yan, Akmaral Seitkhan, Maxime Babics, Anand S. Subbiah, Esma Ugur, Fuzong Xu, Lujia Xu, Mingcong Wang, Atteq ur Rehman, Arsalan Razzaq, Jingxuan Kang, Randi Azmi, Ahmed Ali Said, Furkan H. Isikgor, Thomas G. Allen, Denis Andrienko, Udo Schwingenschlögl, Frédéric Laquai, Stefaan De Wolf, 23 June 2022, Science.
DOI: 10.1126/science.abn8910

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Innovative Technology Offers Big Performance Boost to Perovskite–Silicon Tandem Solar Cells Source link Innovative Technology Offers Big Performance Boost to Perovskite–Silicon Tandem Solar Cells

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