Beware of the Local Effects - 2D Perovskites Under the Microscope
Simon Kahmann a b
a Department of Chemical Engineering & Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
b Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, U.K.
Proceedings of Strain and 2D perovskites Seminar (S2DP)
Online, Spain, 2022 July 11th - 11th
Organizers: Loreta A. Muscarella and Rhiannon Kennard
Invited Speaker, Simon Kahmann, presentation 008
Publication date: 13th June 2022

The layered nature of two-dimensional metal halide perovskites (2D HaPs) gives rise to a large exciton binding energy that often leads to efficient radiative recombination of charge carriers. 2D HaPs thus often offer bright luminescence that can be tuned over a large part of the visible and ultraviolet spectral regions - rendering them attractive candidates for applications of light emission and for studying fundamental aspects of exciton physics.

In many cases, such studies are conducted on polycrystalline thin films through techniques that provide a signal averaged over a large sample area, i.e including many different grains and grain boundaries. At the same time data analysis often relies on simplified models, such as a bulk semiconductor picture that neglects the impact of surfaces, interfaces, and the presence of impurity phases.

As a straightforward and non-invasive set of techniques, optical microscopy is both capable of offering a wide array of photophysical insights of 2D HaPs, and at the same time providing a high spatial resolution.

In this talk, I shall give examples of where simplified pictures of bulk semiconductors fail to explain the properties of 2D HaPs, and how their behaviour can be unravelled through a concerted effort of optical microscopy techniques. A combination of hyperspectral PL imaging and Raman spectro-microscopy is especially powerful. The presented findings will underline the important role of local defects, grain boundaries, impurity phases, and the general microstructure of 2D HaPs for both Ruddlesden Popper and Dion Jacobson phases, and how they need to be accounted for to understand macroscopically accessible information.

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