Episode 1: How reduced-dimensional metal halide perovskites are formed

Research on perovskites has progressed rapidly for PV and LEDs, with new solar-cell efficiency records being set at a regular pace. There are hints of the first commercial products reaching the market by 2020, just a decade since perovskite photovoltaics were first discovered. MRS Bulletin presents the impact of a recent advance in this burgeoning field. Read the abstract in Nature Materials (doi:10.1038/s41563-018-0154-x).

Transcript
Welcome to the first episode of the MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics of 3D bioprinting, artificial intelligence and machine learning, bioelectronics, perovskites, quantum materials, robotics, and synthetic biology. My name is Bob Braughler. 

A new study offers key insights into the formation of layered two-dimensional perovskite films known as Ruddlesden–Popper phases, a class of materials that hold promise for stable light-harvesting and light-emitting devices.

Despite being one of the most attractive materials for photovoltaics and light-emitting devices, conventional three-dimensional organic–inorganic perovskites are plagued by instability issues. However, their 2D counterparts, which contain layers of conductive perovskites separated by layers of relatively long organic cations, are much more stable. The cations inhibit charge transport between neighboring conductive inorganic layers. This forms quantum wells, where the charge carriers can freely move in a 2D space, while there is a restriction in the third dimension.

So far, though, not much is understood about their composition or how these materials assemble. To investigate, Edward Sargent and colleagues at the University of Toronto used grazing incidence x-ray scattering on 2D-layered perovskite films as the films formed.

They used methylammonium lead iodide with either phenethylammonium or n-butylammonium cations, and different solvents to make various film samples. They found that intermediate solvent complexes mediated the formation of quantum wells by providing building blocks to grow perovskites as the solvent evaporates out. They also found that changing the cation changed the well distribution.

This understanding could help control the distribution, composition, and orientation of 2D-layered perovskites, properties that influence device performance. The results could be applied to any such material. The researchers say, “This work paves the way toward engineering higher quality materials for more efficient and stable optoelectronic devices.”

This work was published in a recent issue of Nature Materials. My name is Bob Braughler from the Materials Research Society.

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