Mixed A-Cation Perovskites for Solar Cells: Atomic-Scale Insights into Structural Distortion, Hydrogen Bonding, and Electronic Properties

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Abstract

Hybrid lead halide perovskites containing a mixture of A-site cations such as the formamidinium (CH(NH2)2+, FA) and the smaller cesium (Cs+) cations have attracted considerable interest due to their improved stability and solar cell performance. However, the structural changes at the atomic scale and modifications to the optoelectronic properties of these mixed cation perovskites are not fully understood. Here, we investigate the FA1-xCsxPbI3 (x ≤ 0.25) system using a combination of static and dynamic ab initio computational methods. We find that the incorporation of Cs+ cations into the parent FAPbI3 structure induces a chemical pressure or lattice strain effect through Cs/FA ion size mismatch resulting in structural distortion and stronger FA-iodide (N-H···I) hydrogen bonding interactions. The dynamic tilting of PbI6 octahedra and the rotational motion of FA cations are also suppressed, which leads to symmetry-breaking of the lattice. Such symmetry-breaking distortions of the Pb/I lattice give rise to a Rashba-type effect, which spin-splits the frontier electronic bands making the band gap indirect. Our results suggest that the direct-indirect band gap transition may be a factor in the reduced charge-carrier recombination rate in these mixed cation perovskites.

LanguageEnglish
Pages5194-5204
Number of pages11
JournalChemistry of Materials
Volume30
Issue number15
Early online date9 Jul 2018
DOIs
StatusPublished - 14 Aug 2018

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Electronic properties
Cations
Solar cells
Hydrogen bonds
Positive ions
Cesium
Energy gap
Iodides
Electron transitions
Computational methods
Charge carriers
Optoelectronic devices
Ions

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

Cite this

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title = "Mixed A-Cation Perovskites for Solar Cells: Atomic-Scale Insights into Structural Distortion, Hydrogen Bonding, and Electronic Properties",
abstract = "Hybrid lead halide perovskites containing a mixture of A-site cations such as the formamidinium (CH(NH2)2+, FA) and the smaller cesium (Cs+) cations have attracted considerable interest due to their improved stability and solar cell performance. However, the structural changes at the atomic scale and modifications to the optoelectronic properties of these mixed cation perovskites are not fully understood. Here, we investigate the FA1-xCsxPbI3 (x ≤ 0.25) system using a combination of static and dynamic ab initio computational methods. We find that the incorporation of Cs+ cations into the parent FAPbI3 structure induces a chemical pressure or lattice strain effect through Cs/FA ion size mismatch resulting in structural distortion and stronger FA-iodide (N-H···I) hydrogen bonding interactions. The dynamic tilting of PbI6 octahedra and the rotational motion of FA cations are also suppressed, which leads to symmetry-breaking of the lattice. Such symmetry-breaking distortions of the Pb/I lattice give rise to a Rashba-type effect, which spin-splits the frontier electronic bands making the band gap indirect. Our results suggest that the direct-indirect band gap transition may be a factor in the reduced charge-carrier recombination rate in these mixed cation perovskites.",
author = "Dibyajyoti Ghosh and Smith, {Alexander R.} and Walker, {Alison B.} and Islam, {M. Saiful}",
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N2 - Hybrid lead halide perovskites containing a mixture of A-site cations such as the formamidinium (CH(NH2)2+, FA) and the smaller cesium (Cs+) cations have attracted considerable interest due to their improved stability and solar cell performance. However, the structural changes at the atomic scale and modifications to the optoelectronic properties of these mixed cation perovskites are not fully understood. Here, we investigate the FA1-xCsxPbI3 (x ≤ 0.25) system using a combination of static and dynamic ab initio computational methods. We find that the incorporation of Cs+ cations into the parent FAPbI3 structure induces a chemical pressure or lattice strain effect through Cs/FA ion size mismatch resulting in structural distortion and stronger FA-iodide (N-H···I) hydrogen bonding interactions. The dynamic tilting of PbI6 octahedra and the rotational motion of FA cations are also suppressed, which leads to symmetry-breaking of the lattice. Such symmetry-breaking distortions of the Pb/I lattice give rise to a Rashba-type effect, which spin-splits the frontier electronic bands making the band gap indirect. Our results suggest that the direct-indirect band gap transition may be a factor in the reduced charge-carrier recombination rate in these mixed cation perovskites.

AB - Hybrid lead halide perovskites containing a mixture of A-site cations such as the formamidinium (CH(NH2)2+, FA) and the smaller cesium (Cs+) cations have attracted considerable interest due to their improved stability and solar cell performance. However, the structural changes at the atomic scale and modifications to the optoelectronic properties of these mixed cation perovskites are not fully understood. Here, we investigate the FA1-xCsxPbI3 (x ≤ 0.25) system using a combination of static and dynamic ab initio computational methods. We find that the incorporation of Cs+ cations into the parent FAPbI3 structure induces a chemical pressure or lattice strain effect through Cs/FA ion size mismatch resulting in structural distortion and stronger FA-iodide (N-H···I) hydrogen bonding interactions. The dynamic tilting of PbI6 octahedra and the rotational motion of FA cations are also suppressed, which leads to symmetry-breaking of the lattice. Such symmetry-breaking distortions of the Pb/I lattice give rise to a Rashba-type effect, which spin-splits the frontier electronic bands making the band gap indirect. Our results suggest that the direct-indirect band gap transition may be a factor in the reduced charge-carrier recombination rate in these mixed cation perovskites.

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