KAUST researchers have discovered that adding a metal fluoride layer can improve performance by stalling charge recombination in multilayered perovskite silicon tandem solar cells. By King Abdullah University of Science andamp; Technology (KAUST)

Tandem solar cells, which combine silicon-based and perovskite subcells in one device, are anticipated to capture and convert sunlight into power more effectively and more affordably than their single-junction silicon analogs. The pairs of electrons and positively charged holes that are produced when sunlight strikes the perovskite subcell, however, have a tendency to combine again at the interface between the perovskite and the electron-transport layer. Additionally, a mismatch in energy levels at this contact prevents the separation of electrons within the cell. These issues collectively reduce the tandem cells’ open-circuit voltage, or maximum operating voltage, which restricts device performance.

By adding a layer of lithium fluoride between the perovskite and the electron-transport layer, which typically contains the electron-acceptor fullerene, these performance concerns can be partially resolved (C60). However, the devices become unstable because lithium salts easily liquefy and disperse through surfaces. We had to develop an alternative because none of the gadgets could pass the International Electrotechnical Commission’s regular testing procedures. explains Jiang Liu, the lead author and a postdoc in Stefaan De Wolf’s team.

Other metal fluorides, including as magnesium fluoride, have been thoroughly researched by Liu, De Wolf, and others for use as interlayer materials at the perovskite/C60 interface of tandem cells. Prior to adding C60 and the top contact components, they thermally evaporated the metal fluorides on the perovskite layer to create an ultrathin, uniform film with regulated thickness. In accordance with the criteria of the inverted p-i-n solar cell, the interlayers are also very stable and transparent.

While displacing C60 from the perovskite surface, the magnesium fluoride interlayer efficiently boosted electron extraction from the perovskite active layer. This lessened interface charge recombination. Additionally, it improved charge transfer within the subcell.

According to Liu, the resulting tandem solar cell increased its open-current voltage by 50 millivolts and had one of the greatest power conversion efficiencies for perovskite-silicon tandem cells with a validated stable efficiency of 29.3%.

Considering that the best efficiency for common crystalline silicon-based single-junction cells is 26.7 percent, this cutting-edge technique should result in significant performance improvements without raising the cost of fabrication, according to Liu.

The group is developing scalable techniques to construct perovskite-silicon tandem cells with areas more than 200 square centimeters at industrial scale in order to further investigate the practicality of this technology. We are also developing several strategies to obtain highly stable tandem devices that will pass the critical industrial stability protocols, Liu says.

Initial Research: Efficient and stable perovskite-silicon tandem solar cells through contact displacement by MgF x

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