Perovskites with Flipped Crystals Enhance Solar Cells

A new type of 2D-layered perovskite could lead to next-generation stable solar-cell devices and new opto-electronic devices such as light-emitting diodes, lasers, and sensors.

Researchers tweaked its crystal production method and developed a 2D perovskite with outstanding stability and more than triple the material’s previous power conversion efficiency. This could bring perovskite crystals closer to use in the burgeoning solar power industry.

“Crystal orientation has been a puzzle for more than two decades, and this is the first time we’ve been able to flip the crystal in the actual casting process,” says Hsinhan Tsai, a Rice University graduate student at Los Alamos National Laboratory working with senior researcher and study lead coauthor Aditya Mohite.

“This is our breakthrough, using our spin-casting technique to create layered crystals whose electrons flow vertically down the material without being blocked, mid layer, by organic cations,” Tsai says.

Northwestern University scientists created the 2D material used at Los Alamos in the new solar cells. Mercouri G. Kanatzidis, professor of chemistry, and Costas Stoumpos, a postdoctoral fellow in Kanatzidis’ group, had been exploring an interesting 2D material that orients its layers perpendicular to the substrate.

Wanyi Nie, a Los Alamos coauthor of the paper in Nature, notes, “The new 2D perovskite is both more efficient and more stable, both under constant lighting and in exposure to the air, than the existing 3D organic-inorganic crystals.”

The challenge has been to find something that works better than 3D perovskites, which have remarkable photophysical properties and power conversion efficiencies better than 20 percent but are still plagued by poor performance in stress tests of light, humidity, and heat.

Previous work by the Los Alamos team had provided insights into 3D perovskite efficiency recovery, given a little timeout in a dark space, but by shifting to the more resilient 2D approach, the team has had even better results.

The 2D crystals previously studied by the Northwestern team lost power when the organic cations hit the sandwiched gap between the layers, knocking the solar cells down to a 4.73 percent conversion efficiency due to the out-of-plane alignment of the crystals. But applying the hot casting technique to create the more streamlined, vertically aligned 2D material seems to have eliminated that gap.

Currently, the 2D material has achieved 12 percent efficiency.

“We seek to produce single-crystalline thin-films that will not only be relevant for photovoltaics but also for high-efficiency light-emitting applications, allowing us to compete with current technologies,” says Mohite, principal investigator on the project.

The Northwestern portion of the research received support as part of the ANSER Center, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences.

Source: Northwestern University

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