Issue 44, 2021

Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(ii)/Sn(iv) doping


Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3Bi2Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3Bi2Br9 leads to substitution of up to 7% of the Bi(III) ions by equal quantities of Sn(II) and Sn(IV). The nature of the substitutional defects was studied by X-ray diffraction, 133Cs and 119Sn solid state NMR, X-ray photoelectron spectroscopy and density functional theory calculations. The resulting mixed-valence compounds show intense visible and near infrared absorption due to intervalence charge transfer, as well as electronic transitions to and from localised Sn-based states within the band gap. Sn(II) and Sn(IV) defects preferentially occupy neighbouring B-cation sites, forming a double-substitution complex. Unusually for a Sn(II) compound, the material shows minimal changes in optical and structural properties after 12 months storage in air. Our calculations suggest the stabilisation of Sn(II) within the double substitution complex contributes to this unusual stability. These results expand upon research on inorganic mixed-valent halides to a new, layered structure, and offer insights into the tuning, doping mechanisms, and structure–property relationships of lead-free vacancy-ordered perovskite structures.

Graphical abstract: Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(ii)/Sn(iv) doping

Supplementary files

Article information

Article type
Edge Article
09 Jul 2021
04 Oct 2021
First published
05 Oct 2021
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2021,12, 14686-14699

Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(II)/Sn(IV) doping

C. J. Krajewska, S. R. Kavanagh, L. Zhang, D. J. Kubicki, K. Dey, K. Gałkowski, C. P. Grey, S. D. Stranks, A. Walsh, D. O. Scanlon and R. G. Palgrave, Chem. Sci., 2021, 12, 14686 DOI: 10.1039/D1SC03775G

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