Temperature-Independent Dielectric Constant in CsPbBr3 Nanocrystals Revealed by Linear Absorption Spectroscopy

Wenbi Shcherbakov-Wu^a, Peter Sercel^b^,^c, Franziska Krieg^d^,^e, Maksym Kovalenko^d^,^e, William Tisdale^f

^aMassachusetts Institute Of Technology (MIT), Department of Chemistry, Massachusetts Avenue, 77, Cambridge, United States

^bCenter for Hybrid Organic Inorganic Semiconductors for Energy, Golden, CO, USA

^cDepartment of Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA, USA, United States

^dETH Zurich, Laboratory of Inorganic Chemistry, Department of Chemistry & Applied Biosciences, Vladimir-Prelog-Weg, 1, Zürich, Switzerland

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

^fMassachusetts Institute of Technology (MIT), Department of Chemical Engineering, Green Bldg, Cambridge, MA 02142, EE. UU., Cambridge, United States

Proceedings of Internet Conference for Quantum Dots (iCQD)

Online, Spain, 2020 July 14th - 17th

Organizers: Quinten Akkerman, Raffaella Buonsanti, Zeger Hens and Maksym Kovalenko

Poster, Wenbi Shcherbakov-Wu, 086
Publication date: 3rd July 2020

ePoster:

CsPbBr₃ nanocrystals (NCs) have attracted much attention over the past five years due to their exceptional optoelectronic properties and potential applications in devices such as light-emitting diodes (LEDs), lasers, and single-photon emitters. However, their fundamental photophysical properties, especially at low temperatures, are still under active debate. To date, almost all of the reports have used photoluminescence (PL) alone to infer the lattice dynamics in these materials. Here, we measure both the temperature-dependent (35 K - 300 K) absorption and PL spectra of zwitterionic ligand-capped CsPbBr₃ NCs with four different edge lengths (L = 4.9 - 13.2 nm). The excitonic transitions observed in the absorption spectra can be explained with an effective mass model considering the quasicubic NC shape and non-parabolicity of the electronic bands. We observe a temperature-dependent Stokes shift; while the trend is similar to the Stokes shift observed in both MAPbBr₃ and CsPbBr₃ single crystals, it does not approach zero at cryogenic temperatures, pointing to an additional contribution intrinsically present in the NCs. Surprisingly, the effective dielectric constant determined from the best fit model parameters is independent of temperature, contrary to the previous report that the change in dielectric constant leads to the Stokes shift temperature dependence. Overall, our study sheds light on the fundamental lattice dynamics in these materials, and can potentially be used to guide future material optimization for device applications.

References:

[1] Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Loredana Protesescu, Sergii Yakunin, Maryna I. Bodnarchuk, Franziska Krieg, Riccarda Caputo, Christopher H. Hendon, Ruo Xi Yang, Aron Walsh, and Maksym V. Kovalenko, Nano Letters 2015 15 (6), 3692-3696.

[2] Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability. Franziska Krieg, Stefan T. Ochsenbein, Sergii Yakunin, Stephanie ten Brinck, Philipp Aellen, Adrian Süess, Baptiste Clerc, Dominic Guggisberg, Olga Nazarenko, Yevhen Shynkarenko, Sudhir Kumar, Chih-Jen Shih, Ivan Infante, and Maksym V. Kovalenko, ACS Energy Letters 2018 3 (3), 641-646.

[3] Quasicubic model for metal halide perovskite nanocrystals. Peter C. Sercel, John L. Lyons, Noam Bernstein, Alexander L. Efros, The Journal of Chemical Physics 2019 151:23.

Acknowledgements:

Spectroscopic characterization at MIT was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under award no. DE-SC0019345. Theoretical modelling of the exciton level structure at Caltech was supported as part of the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science within the U.S. Department of Energy. Nanocrystal synthesis and characterization at ETH was supported by the Swiss Federal Commission for Technology and Innovation (CTI-No. 18614.1 PFNM-NM).

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