Proceedings of Online Meetup: Shape-Controlled Nanocrystals: Synthesis, Characterization Methods and Applications (ShapeNC)
Publication date: 6th May 2020
Controlling the structure of layered hybrid metal halide perovskites, such as the Ruddlesden-Popper (R-P) phases, is challenging because of their tendency to form mixtures of varying composition. Colloidal growth techniques, such as antisolvent precipitation, can form dispersions of particles with properties that match the bulk properties of layered R-P phases, but controlling the composition of these particles remains challenging. Here, we explore the microstructure of particles of R-P phases of methylammonium lead iodide prepared by antisolvent precipitation from ternary mixtures of different alkylammonium cations, where one cation is able to form perovskite phases (CH3NH3+) and the other two promote layered structures as spacers (e.g. C4H9NH3+ and C12H25NH3+). We illustrate how competition between cations that act as spacers between layers, or as grain-terminating ligands, determines if colloidal nanocrystals or layered R-P crystallites form in solution. Optical measurements reveal that quantum well dimensions can be tuned by engineering the ternary cation composition. Transmission synchrotron wide-angle X-ray scattering and small angle neutron scattering reveal changes in the structure of colloids in solvent and after deposition into thin films. In particular, we find that spacers can alloy between R-P layers if they share common steric arrangements, but tend to segregate into polydisperse R-P phases if they do not mix. This study provides a framework to compare the microstructure of colloidal layered perovskites and suggests clear avenues to control phase and colloidal morphology.
Materials synthesis and structural characterization were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award Number DE-SC-0012541. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by U.S. Department of Energy, Office of Science, Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Access to the NGB30M SANS instrument was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under agreement no. DMR-1508249. We acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce, in providing the neutron research facilities used in this work. We also thank Dr. Yun Liu from NIST Center for Neutron Research for assistance performing neutron scattering experiments. The research reported here also made use of the shared facilities of the UCSB MRSEC (NSF DMR 1720256), a member of the Materials Research Facilities Network (www.mrfn.org). The authors thank Tanvi Sheth, Serena Seshadri and Tuan Nguyen for assistance with exploratory experiments and helpful discussion.
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