Incorporating Large A Cations into Lead Iodide Perovskite Cages: Relaxed Goldschmidt Tolerance Factor and Impact on Exciton-Phonon Interaction.

Author(s) Fu, Y.; Hautzinger, M.P.; Luo, Z.; Wang, F.; Pan, D.; Aristov, M.M.; Guzei, I.A.; Pan, A.; Zhu, X.; Jin, S.
Journal ACS Cent Sci
Date Published 2019 Aug 28

The stability and formation of a perovskite structure is dictated by the Goldschmidt tolerance factor as a general geometric guideline. The tolerance factor has limited the choice of cations (A) in 3D lead iodide perovskites (APbI), an intriguing class of semiconductors for high-performance photovoltaics and optoelectronics. Here, we show the tolerance factor requirement is relaxed in 2D Ruddlesden-Popper (RP) perovskites, enabling the incorporation of a variety of larger cations beyond the methylammonium (MA), formamidinium, and cesium ions in the lead iodide perovskite cages for the first time. This is unequivocally confirmed with the single-crystal X-ray structure of newly synthesized guanidinium (GA)-based (-CHNH)(GA)PbI, which exhibits significantly enlarged and distorted perovskite cage containing sterically constrained GA cation. Structural comparison with (-CHNH)(MA)PbI reveals that the structural stabilization originates from the mitigation of strain accumulation and self-adjustable strain-balancing in 2D RP structures. Furthermore, spectroscopic studies show a large A cation significantly influences carrier dynamics and exciton-phonon interactions through modulating the inorganic sublattice. These results enrich the diverse families of perovskite materials, provide new insights into the mechanistic role of A-site cations on their physical properties, and have implications to solar device studies using engineered perovskite thin films incorporating such large organic cations.

DOI 10.1021/acscentsci.9b00367
ISSN 2374-7943
Citation ACS Cent Sci. 2019;5(8):13771386.

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