Karmakar Abhoy, Bhattacharya Amit, Sarkar Diganta, Bernard Guy M, Mar Arthur, Michaelis Vladimir K
Department of Chemistry, University of Alberta Edmonton Alberta T6G 2G2 Canada
Chem Sci. 2020 Dec 30;12(9):3253-3263. doi: 10.1039/d0sc05614f.
Tin halide perovskites are promising candidates for lead-free photovoltaic and optoelectronic materials, but not all of them have been well characterized. It is essential to determine how the bulk photophysical properties are correlated with their structures at both short and long ranges. Although CsSnCl is normally stable in the cubic perovskite structure only above 379 K, it was prepared as a metastable phase at room temperature. The transition from the cubic to the monoclinic phase, which is the stable form at room temperature, was tracked by solid-state Cs NMR spectroscopy and shown to take place through a first-order kinetics process. The complete solid solution CsSn(Cl Br ) (0 ≤ ≤ 1) was successfully prepared, exhibiting cubic perovskite structures extending between the metastable CsSnCl and stable CsSnBr end-members. The NMR spectra of CsSnBr samples obtained by three routes (high-temperature, mechanochemical, and solvent-assisted reactions) show distinct chemical shift ranges, spin-lattice relaxation parameters and peak widths, indicative of differences in local structure, defects and degree of crystallinity within these samples. Variable-temperature Sn spin-lattice relaxation measurements reveal spontaneous mobility of Br atoms in CsSnBr. The degradation of CsSnBr, exposed to an ambient atmosphere for nearly a year, was monitored by NMR spectroscopy and powder X-ray diffraction, as well as by optical absorption spectroscopy.
卤化锡钙钛矿是无铅光伏和光电子材料的有前途的候选者，但并非所有卤化锡钙钛矿都得到了充分表征。确定体相光物理性质在短程和长程范围内如何与其结构相关至关重要。尽管CsSnCl通常仅在379 K以上才稳定存在于立方钙钛矿结构中，但它在室温下被制备为亚稳相。通过固态Cs NMR光谱跟踪了从立方相到单斜相（室温下的稳定形式）的转变，并表明其通过一级动力学过程发生。成功制备了完整的固溶体CsSn(Cl Br ) (0 ≤ ≤ 1)，其呈现出在亚稳的CsSnCl和稳定的CsSnBr端元之间延伸的立方钙钛矿结构。通过三种途径（高温、机械化学和溶剂辅助反应）获得的CsSnBr样品的NMR光谱显示出不同的化学位移范围、自旋晶格弛豫参数和峰宽，表明这些样品在局部结构、缺陷和结晶度方面存在差异。变温Sn自旋晶格弛豫测量揭示了CsSnBr中Br原子的自发迁移率。通过NMR光谱、粉末X射线衍射以及光吸收光谱监测了暴露在环境气氛中近一年的CsSnBr的降解情况。
