Kubicki Dominik J, Saski Marcin, MacPherson Stuart, Gal Kowski Krzysztof, Lewiński Janusz, Prochowicz Daniel, Titman Jeremy J, Stranks Samuel D
Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, U.K.
Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge, CB3 0AS, U.K.
Chem Mater. 2020 Oct 13;32(19):8129-8138. doi: 10.1021/acs.chemmater.0c01255. Epub 2020 Sep 17.
All-inorganic double perovskites (elpasolites) are a promising potential alternatives to lead halide perovskites in optoelectronic applications. Although halide mixing is a well-established strategy for band gap tuning, little is known about halide mixing and phase segregation phenomena in double perovskites. Here, we synthesize a wide range of single- and mixed-halide CsAgBiX (X = Cl, Br, and I) double perovskites using mechanosynthesis and probe their atomic-level microstructure using Cs solid-state MAS NMR. We show that mixed Cl/Br materials form pure phases for any Cl/Br ratio while Cl/I and Br/I mixing is only possible within a narrow range of halide ratios (<3 mol % I) and leads to a complex mixture of products for higher ratios. We characterize the optical properties of the resulting materials and show that halide mixing does not lead to an appreciable tunability of the PL emission. We find that iodide incorporation is particularly pernicious in that it quenches the PL emission intensity and radiative charge carrier lifetimes for iodide ratios as low as 0.3 mol %. Our study shows that solid-state NMR, in conjunction with optical spectroscopies, provides a comprehensive understanding of the structure-activity relationships, halide mixing, and phase segregation phenomena in CsAgBiX (X = Cl, Br, and I) double perovskites.
全无机双钙钛矿（铯铅卤石）在光电子应用中是卤化铅钙钛矿颇具潜力的替代物。尽管卤化物混合是一种成熟的带隙调控策略，但对于双钙钛矿中的卤化物混合和相分离现象却知之甚少。在此，我们通过机械合成法制备了一系列单卤化物和混合卤化物的CsAgBiX（X = Cl、Br和I）双钙钛矿，并利用Cs固态核磁共振（MAS NMR）探测其原子级微观结构。我们发现，对于任意Cl/Br比例，混合Cl/Br的材料都能形成纯相，而Cl/I和Br/I混合仅在卤化物比例的窄范围内（<3 mol% I）才有可能实现，比例更高时会导致产物的复杂混合物。我们对所得材料的光学性质进行了表征，结果表明卤化物混合并不会使光致发光（PL）发射产生明显的可调性。我们发现，碘化物的掺入尤其有害，因为即使碘化物比例低至0.3 mol%，它也会淬灭PL发射强度和辐射电荷载流子寿命。我们的研究表明，固态核磁共振与光谱学相结合，能够全面理解CsAgBiX（X = Cl、Br和I）双钙钛矿中的结构 - 活性关系、卤化物混合和相分离现象。
