CsxPbyBrz型钙钛矿纳米材料的可控合成与光学性质研究

RESEARCH ON THE CONTROLLABLE SYNTHESIS AND OPTICAL PROPERTIES OF CSXPBYBRZ - BASED PEROVSKITE NANOCRYSTALS

朱继超

11649059

硕士

化学

权泽卫

2018

2018.7.2

哈尔滨工业大学

深圳

近年来，钙钛矿材料由于其优异的光学和电学性能，受到了广泛的关注，并被大量用于太阳能电池、LED、激光器、光电探测器及存储器件等方面的研究。有机-无机杂化钙钛矿用于太阳能电池时，其光电转换效率已经能够达到23.0%，被认为是未来最有应用前景的材料之一。但杂化钙钛矿对热、氧、极性溶剂等非常敏感，长期稳定性差，极大束缚了其应用。而全无机卤化钙钛矿不仅具有很好的热、氧稳定性，而且其同样具有可与杂化钙钛矿相媲美的光电特性，因而人们对它的关注也与日俱增。CsPbBr3 作为全无机卤化钙钛矿中稳定性最佳的材料，大量的研究工作聚焦于其结构、带隙的调控，以实现其光电性能的可控调节。相比于典型的ABX3 型钙钛矿材料，具有不同化学计量比的CsxPbyBrz 钙钛矿衍生物则少有研究，同作为钙钛矿家族中的成员，其可能具有不同的晶体结构并展现出完全不同的化学、物理特性。但由于对钙钛矿衍生物Cs4PbBr6 和CsPb2Br5 的研究相对较少，人们对其光学性质和其他性质的认识一直存在争议，也使得Cs4PbBr6 和CsPb2Br5 尚且难以真正应用于特定应用当中，其争议的根源则是纯相衍生物的制备。由于CsPbBr3 具有非常好的光学特性，即使是极少量的CsPbBr3 存在也会产生较强的荧光，且其常寄生吸附于大块衍生物晶体中，从而让人难以分辨荧光的来源是衍生物还是CsPbBr3。因此，针对纯相衍生物难以制备的问题，我们设计了一种简单易行的方法巧妙地选择性合成出了衍生物Cs4PbBr6 和CsPb2Br5，并且还探索出了一种可控合成不同尺寸CsPbBr3 纳米晶的新方法，同时，我们还通过后处理的方法进一步验证了直接合成法中不同产物形成机理的合理性。本课题的主要研究内容如下：首先，在低DMF 试剂用量时，通过改变DMF 用量，研究了不同DMF 用量对CsPbBr3 纳米晶生长的影响，发现在0.1 mL–1 mL DMF 范围内，随DMF量的增加，CsPbBr3 的晶粒尺寸逐渐增大，并表现出量子尺寸效应，其荧光随晶粒尺寸变大而逐渐红移。低含量DMF 时，DMF 对CsPbBr3 纳米晶的晶粒尺寸具有调控作用，利用这一已知条件，通过进一步加大DMF 的用量研究高含量DMF 时，其对钙钛矿产物的影响，发现4 mL DMF 时可制得CsPbBr3 的衍生物Cs4PbBr6，15 mL DMF时则制得其另一衍生物CsPb2Br5。针对产物的这种差异性，对不同DMF 含量的情况进行了精细化控制实验，同时分别研究了不同油胺和DMF 含量作用下，其对产物的影响，分析了不同产物的形成机理。通过用配体试剂对CsPbBr3 溶液进行后处理，研究了CsPbBr3 与其衍生物之间的转变关系，发现用DMF 对CsPbBr3 后处理可使其转变为CsPb2Br5，且CsPbBr3 对DMF 有极高的敏感性；用油胺对CsPbBr3 进行后处理则可使其转变为Cs4PbBr6，但结晶性较差。后处理产物的结果与直接合成法的结果比较符合，进一步验证了不同产物形成机理的正确性。

In recent years, perovskite materials have attracted great attention owing to their outstanding optical and electronic features and wdie applications on solar cells, lightemitting diodes, lasers, photodetectors and memory devices. As organic-inorganic hybrid perovskite is used for solar cell, its photoelectric conversion efficiency can be as high as 23.0%, and thus is considered as one of the most promising materials in the future. However, due to the issue of high sensitivity to heat, oxygen and polar solvent, the long-term stability of organic-inorganic perovskite is limited, greatly restricting its application in many aspects. All-inorganic perovskite not only has a good stability on heat and oxygen, but also has comparable photoelectric properties with hybrid perovskite, receiving more and more attention. CsPbBr3 perovskite is very stable in all inorganic perovskites, and a lot of work have been focused on the regulation of its structure and bandgap in order to achieve its tunable optical and electronic properties. Lead halide perovskite derivatives that have the same constituent elements but varied stoichiometric ratios compared to traditional ABX3 perovskite, are rarely studied, which may possesses different crystal symmetries and exhibits distinctly different chemical/physical properties. Owing to the relatively less reports on perovskite derivatives, there are still limited understanding about the physical properties of these CsPbBr3 perovskite derivatives up to now, resulting in the difficulties of applying these derivatives to specific applications. And the origin of such controversies can be attributed to the uneasy synthesis of pure phase derivatives. CsPbBr3 perovskite has superior optical properties and even a slight amount of it can emit bright photoluminescence (PL), while CsPbBr3 usually parasitize its derivative crystals, resulting the misunderstanding of the origin of the PL whether it is belonging to CsPbBr3 or its derivative. Therefore, to solve the difficulty in the synthesis of pure phase perovskite derivatives, a facile and delicate method was designed to controllably prepare Cs4PbBr6 and CsPb2Br5 perovskite derivatives, and CsPbBr3 perovskite nanocrystals with tunable size were also achieved. Furthermore, a post-treated method was also provided to further prove the rationality of the formation mechanism in the derect synthesis process. The main research achievements in this project are as below:When the amount of DMF is low, the influence of different DMF amount on the crystal growth of CsPbBr3 perovskite was explored by adjusting the DMF amount. As the DMF amount increases at the range of 0.1 mL–1 mL, the sizes of CsPbBr3 perovskite nanocrystals become bigger gradually and exhibit apparently quantum size effect, that is, fluorescence peak redshifts as the sizes become larger.On account that at the situation of low DMF amount, DMF can have a regulating effect on the crystal size of CsPbBr3 perovskite, the diversity of products are expected when the DMF amount is high. By further increasing the DMF amount, pure phase Cs4PbBr6 can be obtained at 4 mL DMF and pure CsPb2Br5 at 15 mL DMF. Considering the diversity of products, intensive controllable experiments were carried out at different DMF amount and oleylamine amount, respectively, in order to reveal the effect of DMF.A post-treated method was also used to explore the transformation relationship between CsPbBr3 perovskite and its derivatives. It can be found that CsPbBr3 perovskite has a high sensitivity on DMF and DMF can induce the transformation from CsPbBr3 perovskite to CsPb2Br5, while oleylamine can induce the formation of Cs4PbBr6 but with low crystallinity. The results of post-treated method are consistent with that in direct synthesis and further confirm the validity of the formation mechanism of different products.

CsPbBr3 Cs4PbBr6 CsPb2Br5 钙钛矿衍生物 N,N-二甲基甲酰胺 量子尺寸效应

CsPbBr3 Cs4PbBr6 CsPb2Br5 perovskite derivatives N,Ndimethylformamide quantum size effect

中文

联合培养

南方科技大学

朱继超. CsxPbyBrz型钙钛矿纳米材料的可控合成与光学性质研究[D]. 深圳. 哈尔滨工业大学,2018.