The remarkable optoelectronic properties of perovskites are driving a revolution in how we harvest energy from sunlight and light emission applications (displays and lighting). Of particular note are the organic-inorganic hybrid perovskites, where the combination of the organic layers and inorganic frameworks empower a greater level of control over the molecular structure. The inorganic frameworks are typically based on lead since these have shown the greatest stability. When these inorganic frameworks are based on an element such as tin, the tin atoms are shown to very easily lose electrons (oxidation Sn²⁺ to Sn⁺⁴ ), which causes decomposition of the perovskite. Recent studies have explored the use of an old metallurgy trick, making an alloy. By adding certain amounts of lead to the tin systems, the perovskite frameworks can be stabilized.

The lead / tin perovskite alloys have received a great deal of attention. Not only does this approach reduce the amount of lead that is used (lead is considered harmful to work with and difficult to dispose of), but the stability of these systems is enhanced, and early reports show some very interesting electronic and optical properties.

However, these alloy systems have not been comprehensively investigated, which is where this collaboration, led by IMOD member Mercouri Kanatzidis (Northwestern University), originates. This collaboration, that includes domestic and international research groups, employs synthetic, crystallographic, theoretical chemistry and solid-state NMR analytical approaches to develop a systematic understanding of how structural variation influences physical and electronic properties.

In addition to the Kanatzidis Group (Northwestern University), the Sargent Group (Northwestern University), the Li Group (Dalian National Laboratory for Clean Energy), the Reddy Group (University of Lille), and the Dravid Group (Northwestern University), all brought a wealth of expertise to investigate this important class of perovskites.

“Collaboration was critical to the success of this work. There were some unusual and unexpected observations being made with these systems, and we needed a whole suite of tools to understand this” said Mercouri.

New members of the mixed lead / tin perovskites were presented in this work, with extensive insight into the chemical nature and structure. Both systems showed low bandgaps and narrow-band emission, both properties that are very desirable for light-emission applications.

Mercouri was excited by the synergy developed by the collaborative approach “We have enhanced the fundamental understanding of 2D perovskite materials. Exploring observations through experimental research that could have not been predicted by theory has enabled the production of new materials that could be further developed for a range of different devices and applications. Further, we were able to train a diverse group of scientists, across a range of different groups, in a range of different disciplines and techniques on how to work together to solve a big problem”

For the IMOD team this is only the start for these alloyed perovskites. They plan to select the top performers and work with the other groups in the IMOD community to take them forward for new optoelectronic devices.