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中国物理学会期刊

大尺寸高质量CH3NH3PbCl3钙钛矿单晶的生长机理、相转变与光学性能

Growth mechanism, phase transition and optical properties of large-size and high-quality perovskite CH3NH3PbCl3 single crystal

CSTR: 32037.14.aps.72.20230097
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  • 在传统逆温差结晶法基础上, 通过引入高质量籽晶, 采用籽晶诱导逆温差结晶法生长出尺寸为11 mm ×11 mm × 2 mm的CH3NH3PbCl3钙钛矿单晶. X射线衍射和Rietveld精修结果表明, 室温下CH3NH3PbCl3单晶是立方相, 其空间群为Pm\bar3m, 晶格常数a = 0.56877 nm. 偏光显微镜研究结果表明, CH3NH3PbCl3单晶的生长机理遵循光滑界面的台阶横向长大机制, 并沿着台阶的外法线方向长大. 变温拉曼光谱研究表明CH3NH3PbCl3单晶在温度160 K发生了正交-四方相转变, 但四方相结构不稳定, 存在的温度区间非常狭窄, 故再次转变为立方相(Pm\bar3m). 紫外-可见-近红外吸收光谱和光致发光谱研究表明, CH3NH3PbCl3单晶的吸收截止边约在波长442 nm, 光致发光峰为450 nm, 通过拟合计算得到其带隙值约为2.93 eV, 稍大于第一性原理计算的理论帯隙值(2.55 eV), 分析认为这与籽晶的引入有关, 因为籽晶作为异质形核的核心被引入晶体生长过程中, 使晶格对称性下降, 引起CH3NH3PbCl3帯隙增大.

     

    According to the phenomenon that the solubility of CH3NH3PbCl3 decreases with the increase of temperature in different solvents, CH3NH3PbCl3 perovskite single crystal with a maximum dimension of 11 mm × 11 mm × 2 mm is grown by introducing a high-quality seed crystal via the seed-induced inverse temperature crystallization method in this work. X-ray diffraction and Rietveld refinements show that the full widths at half maximum (FWHM) of CH3NH3PbCl3 single crystal diffraction peaks are 0.1527°, 0.1353°, 0.2295° and 0.3452°, corresponding to the crystal plane indices of (100), (200), (300) and (400), respectively. And there are no miscellaneous peaks, indicating a good crystal quality. As a result, CH3NH3PbCl3 single crystal is of cubic phase at room temperature, its space group belongs to Pm \bar3 m, and the lattice constant is a = 0.56877 nm. The surface morphology and growth mechanism of CH3NH3PbCl3 crystal are investigated by using a polarizing microscope. It is found that its growth mechanism follows the step horizontal growing mechanism of smooth interface, and its growth direction (that is, step movement direction) is along the outward normal direction of the step. The structural symmetry of CH3NH3PbCl3 crystal is studied by variable temperature Raman spectroscopy, which reveals an orthogonal-tetragonal phase transition at 160 K. But the tetragonal phase structure is not stable, and its temperature range is very narrow. As temperature rises gradually, the tetragonal phase again transforms into a cubic phase (Pm\bar3m). Results of UV-Vis-NIR absorption and photoluminescence spectra show that the absorption cutoff of CH3NH3PbCl3 crystal is about 442 nm, and the photoluminescence peak is 450 nm. Thereupon, its band gap is obtained to be about 2.93 eV by a linear fit of Tauc formula, which is slightly higher than the theoretical value of 2.55 eV calculated by first principles simulation. We believe that it is related to the seed crystal, which is introduced into the crystal growth process as the core of heterogeneous nucleation and thus making the lattice more distorted. The lower the lattice symmetry of CH3NH3PbCl3, the larger the band gap is, that is, the lattice symmetry determines the degree of distortion for inorganic PbCl6 octahedral frameworks, resulting in an increase of band gap for CH3NH3PbCl3.

     

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