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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., 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: 06 Oct 2021 12:19

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