student report for Lattice Dynamics in Perovskite halides CsSnX3 with X=I, Br, Cl
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Lattice Dynamics in Perovskite halides CsSnX3 with X=I, Br, Cl
Paper of Ling-yi Huang and Walter R. L. Lambrecht Reported by Wang Maoji SUSTC 2014,12,21
For photovoltaic (Up to15% conversion efficiency last year) Phase transition One predicted peak is missed in experiment for IR
Phases of CsSnX3
Exposure to air for an hour :
Y
or M phase
Stable at high temperature or at
Computational method adopted
The density functional perturbation theory The local density approximation (LDA)
: a a c (M )
0 0 2
(Z ) : a b b
5
Infrared Spectra for
Im : TO phonons Im
1
CsSnI3
CsSnBr3
CsSnCl3
: LO
phonons
2 Im ( ) ( ) n( )c
ห้องสมุดไป่ตู้Negative
Band Structure & DOS
X=I
Lower atomic mass contributes to higher X=Br soft phonon frequency. X=Cl
Band Structure & DOS
Vibration of Cs only contributes to low frequency, while high frequency from the deformation of the tetrahedrons.
Band Structure & DOS
, , , Y for CsSnI3 , , for CsSnBr3 , M for CsSnCl3
Band Structure & DOS
For
,
Soft Phonon mode occurs! Unstable! It comes from the vibrations of halide atoms.
Strong phononphonon scattering
Short lifetime or
Strong broadening
sharp peak
Reference
Ling-yi Huang and Walter R. L. Lambrecht, PHYSICAL REVIEW B 90, 195201 (2014) Hyunsu Sim, S. W. Cheong, and Bog G. Kim, PACS numbers: 71.15.Mb, 77.55.Px, 61.50.Ah, 63.20.D-, 77.84.Bw W.Sleight, Patrick M. Woodward for the degree of Doctor of Philosophy in Chemistry presented on November 22, 1996.
Thanks
The End
Soft Phonon modes and Phase Transition
M 2 M : 1,1,0 / a 0 0
aac
R : 1,1,1 / a 0 0
aac
For glazer notation
Glazer notation
:a b b
Soft Phonon modes and Phase Transition
Contents
CsSnX3
Phonon band structures & DOS Relation between soft phonon modes and phase transition Calculate the IR for the cubic phase
CsSnX3 Background
Cubic: Tetragonal: Orthorhombic: Orthorhombic Yellow: Y Monoclinic Monoclinic : M
Phase transitions of CsSnI3
43.5 5.7 K : 352 5.3K :
Infrared Spectra for
Negligible TO-LO splitting; Not observed. Small splitting; Averaged over TO-LO
Large splitting; TO and LO, respectively.
X=Br
Why couldn’t the lowest mode be observed in IR?
Paper of Ling-yi Huang and Walter R. L. Lambrecht Reported by Wang Maoji SUSTC 2014,12,21
For photovoltaic (Up to15% conversion efficiency last year) Phase transition One predicted peak is missed in experiment for IR
Phases of CsSnX3
Exposure to air for an hour :
Y
or M phase
Stable at high temperature or at
Computational method adopted
The density functional perturbation theory The local density approximation (LDA)
: a a c (M )
0 0 2
(Z ) : a b b
5
Infrared Spectra for
Im : TO phonons Im
1
CsSnI3
CsSnBr3
CsSnCl3
: LO
phonons
2 Im ( ) ( ) n( )c
ห้องสมุดไป่ตู้Negative
Band Structure & DOS
X=I
Lower atomic mass contributes to higher X=Br soft phonon frequency. X=Cl
Band Structure & DOS
Vibration of Cs only contributes to low frequency, while high frequency from the deformation of the tetrahedrons.
Band Structure & DOS
, , , Y for CsSnI3 , , for CsSnBr3 , M for CsSnCl3
Band Structure & DOS
For
,
Soft Phonon mode occurs! Unstable! It comes from the vibrations of halide atoms.
Strong phononphonon scattering
Short lifetime or
Strong broadening
sharp peak
Reference
Ling-yi Huang and Walter R. L. Lambrecht, PHYSICAL REVIEW B 90, 195201 (2014) Hyunsu Sim, S. W. Cheong, and Bog G. Kim, PACS numbers: 71.15.Mb, 77.55.Px, 61.50.Ah, 63.20.D-, 77.84.Bw W.Sleight, Patrick M. Woodward for the degree of Doctor of Philosophy in Chemistry presented on November 22, 1996.
Thanks
The End
Soft Phonon modes and Phase Transition
M 2 M : 1,1,0 / a 0 0
aac
R : 1,1,1 / a 0 0
aac
For glazer notation
Glazer notation
:a b b
Soft Phonon modes and Phase Transition
Contents
CsSnX3
Phonon band structures & DOS Relation between soft phonon modes and phase transition Calculate the IR for the cubic phase
CsSnX3 Background
Cubic: Tetragonal: Orthorhombic: Orthorhombic Yellow: Y Monoclinic Monoclinic : M
Phase transitions of CsSnI3
43.5 5.7 K : 352 5.3K :
Infrared Spectra for
Negligible TO-LO splitting; Not observed. Small splitting; Averaged over TO-LO
Large splitting; TO and LO, respectively.
X=Br
Why couldn’t the lowest mode be observed in IR?