Identifying and controlling phase purity in 2D hybrid perovskite thin films
Identifying and controlling phase purity in 2D hybrid perovskite thin films
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DOI：
10.1039/c8ta05475d
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发表时间：
2018-11-28
影响因子：
11.9
通讯作者：
Docampo, Pablo
中科院分区：
文献类型：
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作者：
Hu, Yinghong;Spies, Laura M.;Docampo, Pablo
二维(2D)混合钙钛矿由于其巨大的结构和电子变化而引起了人们的极大关注，使这类半导体在光伏、发光二极管和激光方面具有很大的吸引力。2D钙钛矿由巨大的有机阳离子片层交替地夹在卤化铅八面体的层中组成。这些材料的性能强烈地依赖于八面体层的厚度，由层中的八面体薄片的数量n定义。因此，控制层厚度纯度(即最小化n中的扩散)对于任何2D钙钛矿薄膜的应用都是重要的。在此，我们发现，在前驱体溶液中使用合理选择的溶剂添加剂为控制2D钙钛矿薄膜的晶型无序提供了一种简便的方法。与无溶剂添加剂的传统快速晶化方法相比，我们的方法大大减小了n在目标值附近的变化。优化后的n=2和n=3薄膜的相纯度通过X射线衍射、UV-Vis吸收和光致发光测试得到了证实。此外，我们发现由添加剂辅助生长的n$2的2D钙钛矿薄膜显示出不寻常的晶体取向，钙钛矿夹层主要平行于衬底，我们将其归因于铅络合溶剂添加剂诱导的缓慢晶化过程。改进的相纯度控制转化为更好地控制2D钙钛矿薄膜的光电性能。此外，n=2和n=3薄膜不同寻常的水平晶体取向使这类可调有机-无机钙钛矿在需要横向电荷传输的应用中具有广阔的应用前景，从而扩大了2D钙钛矿薄膜应用的潜力。
Two-dimensional (2D) hybrid perovskites have attracted considerable attention due to their enormous structural and electronical variability, making this class of semiconductors interesting for photovoltaics, light-emitting diodes and lasers. 2D perovskites consist of sheets of bulky organic cations alternately sandwiched by layers of lead halide octahedra. The properties of these materials strongly depend on the thickness of the octahedra layers, defined by the number of octahedra sheets in a layer, n. Consequently, controlling the layer thickness purity (i. e. minimizing the spread in n) is important for any 2D perovskite thin film application. Here, we show that using rationally chosen solvent additives in the precursor solution offers a facile way to control the crystal disorder in 2D perovskites films. Our method leads to significantly reduced variation in n around the target value relative to films obtained by conventional fast-crystallization methods without solvent additives. The improved phase purity in optimized n = 2 and n = 3 films is verified by X-ray diffraction, UV-vis absorption, and photoluminescence measurements. Additionally, we find that 2D perovskite films with n $ 2 arising from additive-assisted growth exhibit an unusual crystal orientation with the perovskite interlayers predominantly aligned parallel to the substrate, which we assign to the slow crystallization process induced by the lead-complexing solvent additives. Improved control over the phase purity translates into a better control of the optoelectronic properties of 2D perovskite films. Furthermore, the unusual horizontal crystal orientation of n = 2 and n = 3 films makes this family of tunable organic-inorganic perovskites promising for applications where lateral charge transport is desired, thus enlarging the potential for thin film-based applications of the 2D perovskites.