Scientists produce new dimension in perovskite solar cells

In a step that could bring perovskite crystals closer to widespread use in solar cells, researchers from Los Alamos National Laboratory, Northwestern University and Rice University have tweaked their crystal production method. This has allowed them to develop a new type of two-dimensional (2D) layered perovskite with outstanding stability and more than triple the material's previous power conversion efficiency.

"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," said Hsinhan Tsai, a Rice graduate student at Los Alamos working with senior researcher Aditya Mohite, and lead co-author of a paper on this work in Nature. "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."

The 2D perovskite material was initially created at Northwestern University, where Mercouri Kanatzidis, professor of chemistry, and Costas Stoumpos were exploring an interesting 2D perovskite that orients its layers perpendicular to a substrate. "The 2D perovskite opens up a new dimension in perovskite research," said Kanatzidis. "It opens new horizons for next-generation stable solar cell devices and new opto-electronic devices such as light-emitting diodes, lasers and sensors."

"This is a synergy, a very strong synergy between our institutions, the materials design team at Northwestern that designed and prepared high-quality samples of the materials and showed that they are promising, and the Los Alamos team's excellent skills in making solar cells and optimizing them to high performance," said Kanatzidis. A Los Alamos co-author on the paper, Wanyi Nie, noted that "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 boast power conversion efficiencies better than 20%, but are still plagued by poor performance in stress tests of light, humidity and heat. Previous work by the Los Alamos team had revealed that 3D perovskites could recover from the degradation caused by these stresses if given a little timeout in a dark space (see Perovskite solar cells benefit from a few minutes in the dark). By shifting to the more resilient 2D approach, however, the team has produced even better results.

The 2D crystals previously studied by the Northwestern team lost power when the organic cations in the crystals hit the band gap between the layers, knocking the solar cell down to a 4.73% conversion efficiency due to the out-of-plane alignment of the crystals. But applying a hot casting technique to create a more streamlined, vertically-aligned 2D material seems to have eliminated the gap. As a consequence, the 2D material was able to achieve a power conversion efficiency of 12%.

"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," said Mohite.

This story is adapted from material from Los Alamos National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.