Ligand Assisted Transformation of Cubic CsPbBr3 Nanocrystals into Two-Dimensional CsPb2Br5 Nanosheets
Ligand Assisted Transformation of Cubic CsPbBr3 Nanocrystals into Two-Dimensional CsPb2Br5 Nanosheets
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DOI：
10.1021/acs.chemmater.7b04142
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发表时间：
2018-01-09
影响因子：
8.6
通讯作者：
Kamat, Prashant V.
中科院分区：
文献类型：
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作者：
Balakrishnan, Subila K.;Kamat, Prashant V.
金属卤化物掺杂钙钛矿纳米晶具有优异的光致发光和光电性能，在高效太阳能电池和发光二极管中具有重要的应用价值。1− 3固有的软结构和化学不稳定性使这些钙钛矿结构经历晶格内阳离子或阴离子交换的转变。这种化学交换经常被用来调节它们的物理化学性质。4− 8例如，卤化物离子交换反应产生具有覆盖整个可见光谱的可调带隙的混合卤化物钙钛矿。此外，在具有长烷基链阳离子的甲基卤化铅铵（MAPbX）钙钛矿纳米晶体（NC）中的阳离子交换可以产生混合二维（2-D）钙钛矿。12− 15通过控制配体（例如油酸（OA）和油胺（OM））的浓度和组成，还可以改变钙钛矿结构的形状，从零维量子点到二维纳米片或纳米片。[16 - 18]我们现在介绍十二烷基二甲基溴化铵（DDAB）诱导的CsPbBr 3 NC向结晶2-D CsPb 2Br 5纳米片的转化以及与形态变化相关的机理见解。CsPbBr 3钙钛矿纳米晶表现出三种不同的相：正交相（Phnm）、四方相（P4/mbm）和立方相（Pm 3 m）。19，20在较高温度（≥ 130 C）下获得的立方相表现出良好的稳定性。我们采用热注入法，通过在170 ℃下使油酸铯与溴化铅（II）反应来获得立方CsPbBr 3 NC。在氩气氛下，将PbBr 2（0.19mmol）溶解在含有OM（1.52mmol）和OA（1.58mmol）作为配体的十八烯（高沸点溶剂，5 mL）中。然后在170 ℃下快速注入Cs-油酸酯（0.046 mmol），使用丁醇-丙酮（1：2）混合物沉淀NC，然后离心。然后将纯化的NC再分散在甲苯中（合成细节包括在支持信息第3节中）。甲苯中的CsPbBr 3 NC表现出约500 nm的带边（吸收肩）和在507 nm处的发射波长最大值。CsPbBr 3 NC表现出明亮的光致发光（量子产率= 70%），半峰全宽（fwhm）为22 nm，表明NC是单分散的。透射电子显微镜（TEM）分析进一步证实，NC是单分散的，估计尺寸为7±2 nm（图2A）。d间距分析表明，纳米晶具有立方结构的（001）晶面。通过能量色散X射线（EDX）光谱进行元素分析-
Owing to their excellent photoluminescence and optoelec-tronic properties, metal halide hybrid perovskite nanocrystals (NCs) are gaining importance in high efficiency solar cells and light emitting diodes. 1− 3 The intrinsically soft structure and chemical instability renders these perovskite structures to undergo transformations with the exchange of cations or anions within the lattice. Such chemical exchanges have often been utilized to tune their photophysical properties. 4− 8 For example, halide ion exchange reactions produce mixed halide perovskites with a tunable band gap covering the entire visible spectrum. 4, 9− 11 Additionally, the cation exchange in methylammonium lead halide (MAPbX) perovskite nanocrystals (NCs) with long alkyl chain cations can produce hybrid two-dimensional (2-D) perovskites. 12− 15 By controlling the concentration and composition of ligands (eg, oleic acid (OA) and oleylamine (OM)), it is also possible to alter the shapes of perovskite structure, from zero-dimensional quantum dots to 2-D nanoplatelets or nanosheets. 16− 18 We now present dodecyl dimethylammonium bromide (DDAB) induced transformation of CsPbBr3 NCs into crystalline 2-D CsPb2Br5 nanosheets and the mechanistic insights associated with morphological changes. CsPbBr3 perovskite nanocrystallites exhibit three different phases: orthorhombic (Phnm), tetragonal (P4/mbm), and cubic (Pm3m). 19, 20 The cubic phase obtained at higher temperatures (≥ 130 C) exhibits good stability. We employed a hot injection method to obtain cubic CsPbBr3 NCs by reacting Cs-oleate with Pb (II)-bromide at 170 C. The PbBr2 (0.19 mmol) was dissolved in octadecene (high boiling point solvent, 5 mL) containing OM (1.52 mmol) and OA (1.58 mmol) as ligands under an argon atmosphere. Cs-oleate (0.046 mmol) was then quickly injected at 170 C, and the NCs were precipitated using a butanol− acetone (1: 2) mixture followed by centrifugation. The purified NCs were then redispersed in the toluene (synthetic details are included in the Supporting Information, section 3).The absorption and emission spectra of colloidal CsPbBr3 in toluene are presented in Figure 1 A. The CsPbBr3 NCs in toluene exhibit band edge (absorption shoulder) around 500 nm and emission wavelength maximum at 507 nm. The CsPbBr3 NCs exhibit bright photoluminescence (quantum yield= 70%) with a full width at half-maximum (fwhm) of 22 nm indicating the NCs to be monodisperse. The transmission electron microscopy (TEM) analysis further confirms that the NCs are monodisperse with an estimated size of 7±2 nm (Figure 2 A). The d-spacing analysis indicates that the nanocrystals possess (001) plane with a cubic structure. The elemental analyses by energy dispersive X-ray (EDX) spectros-