Enhanced visible light absorption in layered Cs3Bi2Br9 through mixed-valence Sn(ii)/Sn(iv) doping. Issue 44 (13th October 2021)

• Record Type: Journal Article
• Authors: Krajewska, Chantalle J.; Kavanagh, Seán R.; Zhang, Lina; Kubicki, Dominik J.; Dey, Krishanu; Gałkowski, Krzysztof; Grey, Clare P.; Stranks, Samuel D.; Walsh, Aron; Scanlon, David O.; Palgrave, Robert G.
• Is Part Of: Chemical science. Volume 12:Issue 44(2021)
• Page Start: 14686
• Page End: 14699
• Publication Date: 2021-10-13
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc03775g
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : Mixed valence Sn doping of Cs3 Bi2 Br9 leads to broad visible light absorption. Abstract : Lead-free halides with perovskite-related structures, such as the vacancy-ordered perovskite Cs3 Bi2 Br9, are of interest for photovoltaic and optoelectronic applications. We find that addition of SnBr2 to the solution-phase synthesis of Cs3 Bi2 Br9 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, 133 Cs and 119 Sn 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.