Bromine incorporation and suppressed cation rotation in mixed-halide perovskites

Andrew Johnston; Grant Walters; Makhsud I. Saidaminov; Ziru Huang; Koen Bertens; Niina Jalarvo; Edward H. Sargent

doi:10.1021/acsnano.0c05179

Bromine incorporation and suppressed cation rotation in mixed-halide perovskites

Andrew Johnston, Grant Walters, Makhsud I. Saidaminov, Ziru Huang, Koen Bertens, Niina Jalarvo, Edward H. Sargent

Chemical Spectroscopy

Research output: Contribution to journal › Article › peer-review

29 Scopus citations

Abstract

Engineering the composition of perovskite active layers has been critical in increasing the efficiency of perovskite solar cells (PSCs) to more than 25% in the latest reports. Partial substitutions of the monovalent cation and the halogen have been adopted in the highest-performing devices, but the precise role of bromine incorporation remains incompletely explained. Here we use quasi-elastic neutron scattering (QENS) to study, as a function of the degree of bromine incorporation, the dynamics of organic cations in triple-cation lead mixed-halide perovskites. We find that the inclusion of bromine suppresses low-energy rotations of formamidinium (FA), and we find that inhibiting FA rotation correlates with a longer-lived carrier lifetime. When the fraction of bromine approaches 0.15 on the halogen site-a composition used extensively in the PSC literature-the fraction of actively rotating FA molecules is minimized: indeed, the fraction of rotating FA is suppressed by more than 25% compared to the bromine-free perovskite.

Original language	English
Pages (from-to)	15107-15118
Number of pages	12
Journal	ACS Nano
Volume	14
Issue number	11
DOIs	https://doi.org/10.1021/acsnano.0c05179
State	Published - Nov 24 2020

Funding

E.H.S. and all co-authors from the Department of Electrical and Computer Engineering at the University of Toronto acknowledge the financial support from the Ontario Research Fund–Research Excellence Program, the Natural Sciences and Engineering Research Council of Canada (NSERC). M.I.S. acknowledges support from the Banting Postdoctoral Fellowship Program, administered by the Government of Canada. A portion of this research used resources at the Spallation Neutron Source, a U.S. DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The authors gratefully acknowledge Prof. Riccardo Comin and Dr. Xiwen Gong for valuable insights and thoughts on this work.

Funders	Funder number
Ontario Research Fund
Government of Canada
Natural Sciences and Engineering Research Council of Canada

Keywords

Cation dynamics
Energy materials
Perovskite solar cells
Perovskites
Quasi-elastic neutron scattering

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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10.1021/acsnano.0c05179

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abstract = "Engineering the composition of perovskite active layers has been critical in increasing the efficiency of perovskite solar cells (PSCs) to more than 25% in the latest reports. Partial substitutions of the monovalent cation and the halogen have been adopted in the highest-performing devices, but the precise role of bromine incorporation remains incompletely explained. Here we use quasi-elastic neutron scattering (QENS) to study, as a function of the degree of bromine incorporation, the dynamics of organic cations in triple-cation lead mixed-halide perovskites. We find that the inclusion of bromine suppresses low-energy rotations of formamidinium (FA), and we find that inhibiting FA rotation correlates with a longer-lived carrier lifetime. When the fraction of bromine approaches 0.15 on the halogen site-a composition used extensively in the PSC literature-the fraction of actively rotating FA molecules is minimized: indeed, the fraction of rotating FA is suppressed by more than 25% compared to the bromine-free perovskite.",

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AU - Johnston, Andrew

AU - Walters, Grant

AU - Saidaminov, Makhsud I.

AU - Huang, Ziru

AU - Bertens, Koen

AU - Jalarvo, Niina

AU - Sargent, Edward H.

PY - 2020/11/24

Y1 - 2020/11/24

N2 - Engineering the composition of perovskite active layers has been critical in increasing the efficiency of perovskite solar cells (PSCs) to more than 25% in the latest reports. Partial substitutions of the monovalent cation and the halogen have been adopted in the highest-performing devices, but the precise role of bromine incorporation remains incompletely explained. Here we use quasi-elastic neutron scattering (QENS) to study, as a function of the degree of bromine incorporation, the dynamics of organic cations in triple-cation lead mixed-halide perovskites. We find that the inclusion of bromine suppresses low-energy rotations of formamidinium (FA), and we find that inhibiting FA rotation correlates with a longer-lived carrier lifetime. When the fraction of bromine approaches 0.15 on the halogen site-a composition used extensively in the PSC literature-the fraction of actively rotating FA molecules is minimized: indeed, the fraction of rotating FA is suppressed by more than 25% compared to the bromine-free perovskite.

AB - Engineering the composition of perovskite active layers has been critical in increasing the efficiency of perovskite solar cells (PSCs) to more than 25% in the latest reports. Partial substitutions of the monovalent cation and the halogen have been adopted in the highest-performing devices, but the precise role of bromine incorporation remains incompletely explained. Here we use quasi-elastic neutron scattering (QENS) to study, as a function of the degree of bromine incorporation, the dynamics of organic cations in triple-cation lead mixed-halide perovskites. We find that the inclusion of bromine suppresses low-energy rotations of formamidinium (FA), and we find that inhibiting FA rotation correlates with a longer-lived carrier lifetime. When the fraction of bromine approaches 0.15 on the halogen site-a composition used extensively in the PSC literature-the fraction of actively rotating FA molecules is minimized: indeed, the fraction of rotating FA is suppressed by more than 25% compared to the bromine-free perovskite.

KW - Cation dynamics

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KW - Quasi-elastic neutron scattering

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Bromine incorporation and suppressed cation rotation in mixed-halide perovskites

Abstract

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Keywords

UN SDGs

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