Weerd Chris de, Lin Junhao, Gomez Leyre, Fujiwara Yasufumi, Suenaga Kazutomo, Gregorkiewicz Tom
Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
National Institute of Advanced Industrial Science and Technology (AIST), AIST Central 5, Tsukuba 305-8565, Japan.
J Phys Chem C Nanomater Interfaces. 2017 Sep 7;121(35):19490-19496. doi: 10.1021/acs.jpcc.7b05752. Epub 2017 Aug 10.
Nanocrystals of all-inorganic cesium lead halide perovskites (CsPbX, X = Cl, Br, I) feature high absorption and efficient narrow-band emission which renders them promising for future generation of photovoltaic and optoelectronic devices. Colloidal ensembles of these nanocrystals can be conveniently prepared by chemical synthesis. However, in the case of CsPbBr, its synthesis can also yield nanocrystals of CsPbBr and the properties of the two are easily confused. Here, we investigate in detail the optical characteristics of simultaneously synthesized green-emitting CsPbBr and insulating CsPbBr nanocrystals. We demonstrate that, in this case, the two materials inevitably hybridize, forming nanoparticles with a spherical shape. The actual amount of these CsPbBr nanocrystals and nanohybrids increases for synthesis at lower temperatures, i.e., the condition typically used for the development of perovskite CsPbBr nanocrystals with smaller sizes. We use state-of-the-art electron energy loss spectroscopy to characterize nanoparticles at the single object level. This method allows distinguishing between optical characteristics of a pure CsPbBr and CsPbBr nanocrystal and their nanohybrid. In this way, we resolve some of the recent misconceptions concerning possible visible absorption and emission of CsPbBr. Our method provides detailed structural characterization, and combined with modeling, we conclusively identify the nanospheres as CsPbBr/CsPbBr hybrids. We show that the two phases are independent of each other's presence and merge symbiotically. Herein, the optical characteristics of the parent materials are preserved, allowing for an increased absorption in the UV due to CsPbBr, accompanied by the distinctive efficient green emission resulting from CsPbBr.
全无机铯铅卤化物钙钛矿（CsPbX，X = Cl、Br、I）的纳米晶体具有高吸收和高效窄带发射特性，这使其在下一代光伏和光电器件领域颇具潜力。这些纳米晶体的胶体集合体可通过化学合成方便地制备。然而，对于CsPbBr而言，其合成过程也可能产生CsPbBr₃纳米晶体，且二者性质容易混淆。在此，我们详细研究了同时合成的绿色发光CsPbBr₂和绝缘CsPbBr₃纳米晶体的光学特性。我们证明，在这种情况下，这两种材料不可避免地会发生杂化，形成球形纳米颗粒。在较低温度下合成时，这些CsPbBr₃纳米晶体和纳米杂化物的实际产量会增加，即通常用于制备尺寸较小的钙钛矿CsPbBr₂纳米晶体的条件。我们使用最先进的电子能量损失谱在单个物体水平上对纳米颗粒进行表征。这种方法能够区分纯CsPbBr₂和CsPbBr₃纳米晶体及其纳米杂化物的光学特性。通过这种方式，我们解决了一些近期关于CsPbBr₃可能的可见光吸收和发射的误解。我们的方法提供了详细的结构表征，并结合建模，最终确定纳米球为CsPbBr₂/CsPbBr₃杂化物。我们表明这两个相彼此独立存在并共生融合。在此，母体材料的光学特性得以保留，由于CsPbBr₂，在紫外光区的吸收增加，同时伴随着CsPbBr₃产生的独特高效绿色发射。
