Negative Pressure Engineering with Large A-site Cations in 2D Halide Perovskites
Xiaotong Li a
a Northwestern University
Proceedings of Strain and 2D perovskites Seminar (S2DP)
Online, Spain, 2022 July 11th - 11th
Organizers: Loreta A. Muscarella and Rhiannon Kennard
Invited Speaker, Xiaotong Li, presentation 004
Publication date: 13th June 2022

In 3D halide perovskites, the choice of the A-site cage cation is governed by the so-called Goldschmidt tolerance factor. When a large A-site cation exceeding the proper tolerance factor is incorporated, it will cause significant expansive strain in the structure and usually the corner-sharing perovskite structure is disrupted. However in 2D perovskites, the expansion of the perovskite cage can be compensated by the compressive strain induced by the spacer cations to reduce the accumulated strain energy. Expanding the cage is equivalent to exerting “negative pressure” on the perovskite structure, which cannot be achieved by applying physical pressure. We have found that large A-site cations such as formamidinium (FA), methylhydrazinium (MHy), dimethylammonium (DMA), ethylammonium (EA) and guanidinium (GA) can all fit into the cages of 2D perovskites. Increasing the size of the A-site cation can lead to Pb−I bond elongation, bandgap blueshift, lattice softening and PL quenching, providing a perfect model system to study the effect of A-site cations on the photophysical properties of perovskites.

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