Investigation of Highly Stable CsPbBr3 Nanoplatelets by Wide Angle X-ray Total Scattering Methods

Anna Vivani^a, Federica Bertolotti^a, Georgian Nedelcu^b^,^c, Antonio Cervellino^d, Maksym Kovalenko^b^,^c, Norberto Masciocchi^a, Antonella Guagliardi^e

^aUniversity of Insubria, Department of Science and High Technology, Italy

^bDepartment of Chemistry and Applied Biosciences, Department of Chemistry and Applied Biosciences, ETHZ

^cLaboratory for Thin Films and Photovoltaics, Empa – Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland, Überland Strasse, 129, Dübendorf, Switzerland

^dPaul Scherrer Institut (PSI), Forschungsstrasse 111, Villigen, Switzerland

^eCNR-Istituto di Cristallografia (CNR-IC, Bari, Italy, Via Amendola, 122/O, Bari, Italy

Materials for Sustainable Development Conference (MATSUS)
Proceedings of Online nanoGe Fall Meeting 20 (OnlineNFM20)

#PerNC20. Perovskite II - Colloidal Nanocrystals: Synthesis, Spectroscopy, Theory and Applications

Online, Spain, 2020 October 20th - 23rd

Organizers: Gabriele Raino, Maryna Bodnarchuk and Oleksandr Voznyy

Contributed talk, Anna Vivani, presentation 130
Publication date: 4th October 2020

The application of Lead Halide Perovskites (LHP) nanomaterials in many technological fields can take advantage of the physico-chemical properties typical of highly anisotropic morphologies, which can be introduced in nanocrystals by extreme reduction of their thickness [1, 2]. Overcoming critical issues of stability for extremely downsized nanocrystals [3], quasi-2D highly stable CsPbBr₃ nanoplatelets (NPLs) have been synthetized, which exhibit large exciton binding energies and intense blue emission, with PL maximum tunable through fast post-synthetic anionic-exchange reactions. In addition, due to the large surface area, NPLs show a clear tendency to self-assemble, making them particularly promising for LED applications [4]. A precise and accurate atomistic description of LHP structures is of high relevance for formulating reliable considerations over their exceptional properties. An in-depth structural and morphological characterization of CsPbBr₃ NPLs has been carried out by means of a combination of Transmission Electron Microscopy (TEM) imaging and Wide Angle X-ray Total Scattering (WAXTS) techniques. The analysis of high resolution WAXTS data, collected with synchrotron source on colloidal suspensions, was based on the construction of atomistic models of NPLs and the application of the Debye Scattering Equation (DSE) [5]. This advanced approach of structural analysis addresses limitations of traditional X-ray diffraction techniques when applied to complex nanomaterials [6]. In the CsPbBr₃ NPLs case, it enabled to elucidate multiple structural and morphological aspects. Through the analysis, robust information on the NPLs thickness of six PbBr₆ octahedra monolayers was obtained. Moreover, the orthorhombic crystal structure and its specific relative orientation with respect to the NPLs facets were determined. In particular, the results indicate that the NPLs most extended surfaces expose octahedral equatorial bromides, whereas the axial bromides run parallel to the crystallographic b axis that is the most expanded. The overall surface composition remains defective in Br and Cs [7].

References:

[1] [1] Weidman, M. C.; Goodman, A. J.; Tisdale, W. A. Colloidal Halide Perovskite Nanoplatelets: An Exciting New Class of Semiconductor Nanomaterials. Chem. Mater. 2017, 29, 5019-5030.

[2] [2] Li, J.; Luo, L.; Huang, H.; Ma, C.; Ye, Z.; Zeng, J.; He, H. 2D Behaviors of Excitons in Cesium Lead Halide Perovskite Nanoplatelets. J. Phys. Chem. Lett. 2017, 8, 1161-1168.

[3] [3] Bekenstein, Y.; Koscher, B. A.; Eaton, S. W.; Yang, P.; Alivisatos, A. P. Highly Luminescent Colloidal Nanoplates of Perovskite Cesium Lead Halide and Their Oriented Assemblies. J. Am. Chem. Soc. 2015, 137, 16008-16011.

[4] [4] Xing, J.; Zhao, Y.; Askerka, M.; Quan, L. N.; Gong, X.; Zhao, W.; Zhao, J.; Tan, H.; Long, G.; Gao, L.; Yang, Z.; Voznyy, O.; Tang, J.; Lu, Z.-H.; Xiong, Q.; Sargent, E. H. Color-stable highly luminescent sky-blue perovskite light-emitting diodes. Nat. Commun. 2018, 9, 3541.

[5] [5] Debye, P. Zerstreuung von Röntgenstrahlen. Ann. Phys. 1915, 351, 809-823.

[6] [6] Bertolotti, F.; Protesescu, L.; Kovalenko, M. V.; Yakunin, S.; Cervellino, A.; Billinge, S. J. L.; Terban, M. W.; Pedersen, J. S.; Masciocchi, N.; Guagliardi, A. Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals. ACS Nano 2017, 11, 3819-3831.

[7] [7] Bertolotti, F.; Nedelcu G.; Vivani A.; Cervellino A.; Masciocchi N.; Guagliardi A.; Kovalenko M.V. Crystal Structure, Morphology, and Surface Termination of Cyan-Emissive, SixMonolayers-Thick CsPbBr3 Nanoplatelets from X ray Total Scattering. ACS Nano 2019, 13, 12, 14294-14307.

Acknowledgements:

This project was partially supported by MIUR (PRIN-2017L8WW48, Project HY-TEC).

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