Nanoscale TiO 2 coating improves water stability of Cs 2 SnCl 6
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Research Letter
Nanoscale TiO2 coating improves water stability of Cs2SnCl6 Yachun Wang, Weiguang Zhu, and Tiankai Yao , Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA Xiaolei Guo and Gerald S. Frankel, Fontana Corrosion Center, Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210, USA Jie Lian, Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA Address all correspondence to Jie Lian at [email protected] (Received 7 September 2020; accepted 2 November 2020)
Abstract To improve the stability of Cs2SnCl6 under aqueous/moisture environments, we applied a concept of artificial passivation by depositing a protective TiO2 coating of 10 nm on the surface of Cs2SnCl6. Static leaching experiments results indicate that the initial release rates of Cs+ and Cl− are decreased by 20–30 times with TiO2 coating, suggesting its possibility to improve the short-term water/environmental stability of Cs2SnCl6. An amorphous-to-crystalline phase transition in TiO2 film was observed, possibly resulting in degradation of Cs2SnCl6. However, the crystalline TiO2 film still remains after 21 days water exposure and can still act as an effective passivation layer to reduce the release rates of Cs+ and Cl- by as much as about 17 and 7 times, respectively, relative to static leaching without artificial coatings. Therefore, the water/ environmental stability of metal halide perovskite Cs2SnCl6, which is a highly soluble molecular salt, can be enhanced by the nanoscale TiO2 coating as an artificial passivation film.
Introduction Hybrid organic/inorganic halide perovskites display an exceptional tunability in their photoelectric and optoelectronic properties by controlling the halogen anions (e.g., I, Cl, and Br), but experience issues of environmental/water stability and Pb toxicity.[1] Lead-free all-inorganic perovskite Cs2SnIxCl6-x is a defect perovskite derivative with a high oxidation state of Sn4 + , exhibiting tunable bandgaps from 1.3 eV (Cs2SnI6)[1,2] to 3.9 eV (Cs2SnCl6).[3–5] Of particular importance, Cs2SnCl6 displays a highly efficient deep-blue emission at 455 nm when doped with bismuth due to impurity-induced photoluminescence[3] and can be used to develop highly efficient and environmentally-stable and benign solid-state light-emitting diodes. Cs2SnCl6-xBrx can be used as a narrowband photodetector, displaying a high detectivity and response spectra from near violet to orange regimes by varying the chemical composition of the halides and thus the bandgap.[6] Using Bi-doped Cs2SnCl6 nanoparticles with GaN, an inorganic vacancy-ordered perovskite heterojunction photodiode for narrowband and visible-blind UV detection has also been developed,[5] demonstrating excellent narrow-band UV sensitivity, maximum detectivity, and microsecond photo-response. Cs2SnCl6 also has potential as a promising nuclear waste form with very high mass loadings of the problematic longlived radionucli
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