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Phase behavior and substitution limit of mixed cesium-formamidinium lead triiodide perovskites

Charles, Bethan, Weller, Mark T., Rieger, Sebastian, Hatcher, Lauren E. ORCID:, Henry, Paul F., Feldmann, Jochen, Wolverson, Daniel and Wilson, Chick C. 2020. Phase behavior and substitution limit of mixed cesium-formamidinium lead triiodide perovskites. Chemistry of Materials 32 (6) , pp. 2282-2291. 10.1021/acs.chemmater.9b04032

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The mixed cation lead iodide perovskite photovoltaics show improved stability following site substitution of cesium ions (Cs+) onto the formamidinium cation sites (FA+) of (CH(NH2)2PbI3 (FAPbI3) and increased resistance to formation of the undesirable ∂-phase. The structural phase behavior of Cs0.1FA0.9PbI3 has been investigated by neutron powder diffraction (NPD), complemented by single crystal and power X-ray diffraction and photoluminescence spectroscopy. The Cs-substitution limit has been determined to be less than 15%, and the cubic α-phase, Cs0.1FA0.9PbI3, is shown to be synthesizable in bulk and stable at 300 K. On cooling the cubic Cs0.1FA0.9PbI3, a slow, second-order cubic to tetragonal transition is observed close to 290 K, with variable temperature NPD indicating the presence of the tetragonal β-phase, adopting the space group P4/mbm between 290 and 180 K. An orthorhombic phase or twinned tetragonal phase is formed below 180 K, and the temperature for further transition to a disordered state is lowered to 125 K compared to that seen in phase pure α-FAPbI3 (140 K). These results demonstrate the importance of understanding the effect of cation site substitution on structure–property relationships in perovskite materials.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Publisher: American Chemical Society
ISSN: 0897-4756
Funders: EPSRC
Date of First Compliant Deposit: 19 March 2020
Date of Acceptance: 27 February 2020
Last Modified: 07 Nov 2022 19:48

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