Innovative technology provides big performance boost to perovskite-silicon tandem solar cells

Magnesium Fluoride Interlayer Perovskite-Silicon Tandem Solar Cells

Notable performance gains in perovskite–silicon tandem solar cells (such as those pictured here) can be achieved by adding a magnesium fluoride interlayer. Credits: © 2022 Cost; Erkan Aydin

An additional metal fluoride layer enables charge separation and enhances performance in perovskite–silicon tandem solar cells.

Researchers at King Abdullah University of Science and Technology (KAUST) have found that inserting a metal fluoride layer into multilayered perovskite-silicon tandem solar cells can enhance charge recombination and performance.

Tandem solar cells that combine perovskite and silicon-based sub-cells in one device are expected to capture and convert sunlight into electricity better than their traditional single-junction silicon competitors. And they are projected to do so at a lower cost. However, when sunlight hits the perovskite subshell, the resulting pairs of electrons and positively charged holes recombine at the interface between the perovskite and the electron-transport layer. Additionally, a mismatch between energy levels at this interface hinders electron separation within the cell. These issues together reduce the open-circuit voltage, or maximum operating voltage, of tandem cells, which restricts device performance.

By adding a layer of lithium fluoride between the perovskite and the electron-transporting layer, which usually includes the electron-acceptor fullerene (Si).60), these performance concerns can be partially resolved. However, devices become unstable because lithium salts readily liquefy and diffuse through surfaces. “None of the instruments have passed the International Electrotechnical Commission’s standard test protocols, prompting us to make a choice,” says lead author Jiang Liu, a postdoc in Stephen de Wolf’s group.

Liu, de Wolf, and colleagues systematically investigated the potential of other metal fluorides, such as magnesium fluoride, as interlayer materials on perovskite/Si.60 The interface of tandem cells. They thermally evaporated the metal fluoride on the perovskite layer to form an ultrathin uniform film with controlled thickness before adding Si60 and the top contact component. The interlayers are also highly transparent and stable to suit inverted pin solar cell requirements.

The magnesium fluoride interlayer gave C. effectively promoted electron extraction from the perovskite active layer while displacing60 from the perovskite surface. This reduced charge recombination at the interface. It also enhanced charge transport in the subshell.

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

“Given that the best efficiency for mainstream crystalline silicon-based single-junction cells is 26.7 percent, this innovative technology can bring substantial performance gains without adding to the cost of manufacturing,” says Liu.

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

Reference: “Efficient and stable perovskite-silicon tandem solar cell via contact displacement by MgF”x“Jiang Liu, Michel D Bastiani, Erkan Aydin, George T. Harrison, Yajun Gao, Rakesh R. Pradhan, Mathan K. Easwaran, Mukund Mandal, Wenbo Yan, Akmaral Setkhan, Maxim Babix, Anand S. Subbia, Esma Ugur, Fujong Xu , Lujia Xu, Mingkong Wang, Atek ur Rahman, Arslan Razzaq, Jingxuan Kang, Randi Azmi, Ahmed Ali Said, Furkan H. Isikgor, Thomas G. Allen, Denis Andrienko, Udo Schwingenschlogl, Frederic Laquai, 23 Stephen de Wolf June 2022, science,
DOI: 10.1126/science.abn8910

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