[Image above] Three types of large-area solar cells made with 2-D perovskites. Left shows a room-temperature cast film; upper middle is a sample with the problematic band gap; and right shows the hot-cast sample with best energy performance. Credit: Los Alamos National Lab

Perovskite solar cells could be the gold standard in solar energy harvesting technology… if they weren’t so unstable.

Perovskites are lauded for their potential for high efficiency and low cost, so research continues to try to scale up this technology for wide-range applications.  

And stability is the name of the game when it comes to scaling up perovskites.

In May, we reported that a research team from Brown University led by ACerS member Nitin Padture—in collaboration with the National Renewable Energy Laboratory (NREL) and the Chinese Academy of Sciences’ Qingdao Institute of Bioenergy and Bioprocess Technology—are getting closer to making perovskite solar cells a mass-market reality.

“We’ve demonstrated a new procedure for making solar cells that can be more stable at moderate temperatures than the perovskite solar cells that most people are making currently,” Padture says in a Brown University news release about his team’s latest research. “The technique is simple and has the potential to be scaled up, which overcomes a real bottleneck in perovskite research at the moment.”

Now researchers from Los Alamos National Laboratory (LANL), Northwestern University, and Rice University report that they’re tinkering with perovskite crystal production methods, too.  

The team has developed a “new type of 2-D layered perovskite with outstanding stability and more than triple the material’s previous power conversion efficiency,” according to an LANL press release.

And it’s all in the flip of a crystal.

“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,” Hsinhan Tsai, a Rice graduate student at Los Alamos, says in the release. “This is our breakthrough, using our spin-casting technique to create layered crystals whose electrons flow vertically down the material without being blocked, midlayer, by organic cations.”

The perovskite material was initially created at Northwestern, where Mercouri G. Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry, and Costas Stoumpos were exploring an interesting 2-D material that orients its layers perpendicular to the substrate, the release explains.

“The 2-D perovskite opens up a new dimension in perovskite research,” Kanatzidis says. “It opens new horizons for next-generation stable solar cell devices and new optoelectronic devices such as light-emitting diodes, lasers, and sensors.”

Current 3-D perovskites have proven photophysical properties and power conversion efficiencies in excess of 20%, but they don’t stand up well to light, heat, and humidity. So the researchers have accepted the challenge to develop something that trumps the status quo.

The Northwestern team previously studied the 2-D perovskite crystals and found that the crystals “lost power when the organic cations hit the sandwiched gap between the layers, knocking the cells down to a 4.73% conversion efficiency due to the out-of-plane alignment of the crystals,” the release explains.

But they found that their new hot-cast production technique creates a more streamlined, vertically aligned 2-D material, which eliminates that gap and therefore boosts efficiency.

The team says their 2-D material can currently achieve 12% efficiency—and that makes it more applicable for commercial use. 

“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 Aditya Mohite, principal investigator on the project.

Watch this video from LANL for more about the research.

Credit: Los Alamos National Lab; YouTube

The study, published in Nature, is “High-efficiency two-dimensional Ruddlesden-Popper perovskite solar cells” (DOI: 10.1038/nature18306).