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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
- Veröffentlichungsjahr: 2020
Hybrid organic-inorganic perovskites (HOIPs) have attracted substantial interest due to their chemical variability, structural diversity and favorable physical properties the past decade. This materials class encompasses other important families such as formates, azides, dicyanamides, cyanides and dicyanometallates.
The book summarizes the chemical variability and structural diversity of all known hybrid organic-inorganic perovskites subclasses including halides, azides, formates, dicyanamides, cyanides and dicyanometallates. It also presents a comprehensive account of their intriguing physical properties, including photovoltaic, optoelectronic, dielectric, magnetic, ferroelectric, ferroelastic and multiferroic properties. Moreover, the current challenges and future opportunities in this exciting field are also been discussed. This timely book shows the readers a complete landscape of hybrid organic-inorganic pervoskites and associated multifuctionalities.
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Table of Contents
Cover
Preface
Acknowledgements
1 Introduction to Hybrid Organic–Inorganic Perovskites
1.1 Perovskite Oxides
1.2 Evolution from Perovskite Oxides to Hybrid Organic–Inorganic Perovskites
1.3 Classification and Chemical Variations of HOIPs
1.4 Structure, Symmetry, and Property Features of HOIPs
References
2 Hybrid Halide Perovskites
2.1 Synthesis and Chemical Diversity
2.2 Symmetries and Structures
2.3 Phase Transitions
2.4 Physical Properties
References
3 Hybrid Formate Perovskites
3.1 Synthesis and Chemical Diversity
3.2 Symmetries and Structures
3.3 Phase Transitions and Order–Disorder
3.4 Physical Properties
References
4 Hybrid Azide Perovskites
4.1 Synthesis and Structures
4.2 Phase Transitions
4.3 Physical Properties
References
5 Hybrid Dicyanamide Perovskites
5.1 Synthesis and Structures
5.2 Phase Transitions
5.3 Physical Properties
References
6 Hybrid Cyanide Perovskites
6.1 Synthesis and Structures
6.2 Phase Transitions (PT)
6.3 Physical Properties
References
7 Hybrid Dicyanometallate and Borohydride Perovskites
7.1 Hybrid Dicyanometallate Perovskites
7.2 Hybrid Borohydride Perovskites
References
8 Hybrid Hypophosphite Perovskites
8.1 Synthesis
8.2 Symmetries and Structures
8.3 Phase Transitions
8.4 Physical Properties
References
9 Other Perovskite-Like Hybrid Materials and Metal-Free Perovskites
9.1 Hybrid Organic–Inorganic Perchlorates
9.2 Hybrid Organic–Inorganic Tetrafluoroborates
9.3 Metal-Free Perovskites
References
10 Concluding Remarks and Future Perspectives
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Summary of the chemical variabilities, crystal symmetries, and phys...
Chapter 2
Table 2.1 Summary of the chemical variabilities, structures, phase transition...
Table 2.2 Summary of transport characteristics of HOIPs and comparison to oth...
Chapter 3
Table 3.1 Summary of the chemical variabilities, structures, phase transition...
Table 3.2 Summary of magnetic properties of [MA][Mn(HCOO)
3
], [EA][Mn(HCOO)
3
],...
Table 3.3 Summary of magnetic properties of [GUA][M
II
(HCOO)
3
] (X = Mn; Fe; Co...
Table 3.4 Thermal expansion coefficients of lattice and XBU in the range of 1...
Table 3.5 Characteristics of BC effects in three types of compounds with firs...
Chapter 4
Table 4.1 Summary of the chemical variabilities, structures, phase transition...
Chapter 5
Table 5.1 Summary of the chemical variabilities, structures, phase transition...
Table 5.2 Elastic modulus (
E
) and hardness (
H
) properties [16] of [TPrA][M(dc...
Chapter 6
Table 6.1 Summary of the chemical variabilities, structures, phase transition...
Chapter 7
Table 7.1 Summary of the chemical variabilities, structures, phase transition...
Chapter 8
Table 8.1 Summary of the chemical variabilities, structures, phase transition...
Chapter 9
Table 9.1 Summary of the chemical variabilities, structures, phase transition...
Table 9.2 Summary of the chemical variabilities, structures, phase transition...
Table 9.3 Summary of the chemical variabilities, structures, phase transition...
Table 9.4 Summary of the elastic properties of some metal-free perovskites [9...
List of Illustrations
Chapter 1
Figure 1.1 Structure of perovskite mineral, CaTiO
3
. (a) The pseudo-cubic uni...
Figure 1.2 Structures of some prototypic perovskite oxides at ambient condit...
Figure 1.3 Evolution from perovskite oxides to hybrid organic–inorganic pero...
Figure 1.4 Prototypical examples of hybrid organic–inorganic perovskites wit...
Figure 1.5 Structural diversity of the A-site and X-site ions of hybrid orga...
Figure 1.6 Phase transition mechanism in [AZE][Cu(HCOO)
3
]. Colour schemes: N...
Chapter 2
Figure 2.1 The structures of a selection of possible A-site cations used in ...
Figure 2.2 Ambient crystal structures of MAPbCl
3
(a, cubic structure) and MA...
Figure 2.3 Ambient crystal structures of FAPbCl
3
(a, cubic,
) and FAPbI
3
(b...
Figure 2.4 Ambient crystal structures of MASnBr
3
(a, cubic,
) and MASnI
3
(b...
Figure 2.5 Ambient crystal structure of FASnI
3
(orthorhombic,
Amm
2). Hydroge...
Figure 2.6 Ambient crystal structures of MAGeI
3
(a; trigonal,
R
3
m
) and FAGeI
Figure 2.7 The crystal structures of two prototypical halide double perovski...
Figure 2.8 The crystal structures of two prototypical halide double perovski...
Figure 2.9 The crystal structures of two prototypical halide double perovski...
Figure 2.10 Crystal structures of the MAPbI
3
. (a) Cubic phase,
; (b) tetrag...
Figure 2.11 TEM images of MAPbI
3
thin films collected at room temperature (a...
Figure 2.12 Structural phase transition of [AD][RbBr
3
]. (a) Ferroelectric ph...
Figure 2.13 Structural phase transitions of the [MA
2
][KMCl
6
] (M = Y and Gd)....
Figure 2.14 (a) Energy levels for different solar-cell halide HOIPs. (b) Ban...
Figure 2.15 The effects of MA on the calculated bandgap of MAPbI
3
at the DFT...
Figure 2.16 (a) Enlarged view of the band structure around the bandgap of [(...
Figure 2.17 (a) The calculated electronic band structure of [(MA)
2
][TlBiBr
6
]...
Figure 2.18 (a) Calculated electronic band structures and (b) projected dens...
Figure 2.19 The evolution of power conversion efficiency for halide HOIP-bas...
Figure 2.20 (a) MAPbBr
3
and MAPbI
3
nanoparticles deposited on the mesoporous...
Figure 2.21 The IPCE (a) and
I
–
V
(b) plots for MAPbBr
3
/TiO
2
(solid line) and...
Figure 2.22 (a) Wide view TEM image of MAPbI
3
QD deposited TiO
2
. (b) Cross-s...
Figure 2.23 Comparison of (a) photocurrent–voltage and (b) EQE between perov...
Figure 2.24 (a) Schematic illustration of the solar cell structure. Note the...
Figure 2.25 (a) The charge transfer and transport itinerary in a perovskite-...
Figure 2.26 (a) Schematic illustration of the cross-sectional triple-layered...
Figure 2.27 (a) The layer architecture of the inverted planar device. The Nb
Figure 2.28 Top view and cross-sectional SEM images of the solar cell archit...
Figure 2.29 (a) Cross-sectional SEM image showing the modified planar archit...
Figure 2.30 (a) Perovskite film deposition procedures through the vacuum-fla...
Figure 2.31 (A) Schematic illustration of FAPbI
3
nanoparticles crystallized ...
Figure 2.32 Top view SEM images of deposited perovskite layers with differen...
Figure 2.33 (a) The steady-state PL emission spectra of a MAPbI
3
film, evolv...
Figure 2.34 (a) The emission spectra of a vertical microcavity lasing struct...
Figure 2.35 (a) Schematic illustration of the whispery gallery mode achieved...
Figure 2.36 (A) Optical image (a), emission images before (b), and after (c)...
Figure 2.37 (a) Integrated emission intensity in dependence on pumping fluen...
Figure 2.38 (a) Mechanistic illustration of a two-photon absorption process....
Figure 2.39 (a) Device structure of the MAPbI
3−
x
Cl
x
infrared LED. (b) ...
Figure 2.40 (a) Energy-level landscapes of ITO, Buf-HIL, and MAPbBr
3
in the ...
Figure 2.41 (a) Schematic illustration and cross-sectional TEM image (scale ...
Figure 2.42 (a) Cross-sectional SEM image of the MAPbI
3−
x
Cl
x
-based LED...
Figure 2.43 (a) The cross-sectional SEM image of MAPbBr
3
nanorod array and c...
Figure 2.44 (a) Device architecture of the MAPbI
3
film-based photodetector. ...
Figure 2.45 (a) Spatial band diagram of the MAPbCl
3
thin film photodetector....
Figure 2.46 (a) Device structure of the MAPbI
3
-based self-powered photodetec...
Figure 2.47 (a) The device structure of MAPbBr
3
single-crystal X-ray detecto...
Figure 2.48 (a) The parent centric structure with MA cations in the AFE stat...
Figure 2.49 (a) SHG signal as a function of temperature of the [AD][RbBr
3
] p...
Figure 2.50 Rashba-like spin texture in the valence band of the ferroelectri...
Figure 2.51 Structural diagrams of (a) cubic MAPbCl
3
, (b) cubic MAPbBr
3
, and...
Figure 2.52 Elastic modulus (
E
) of single- and double-hybrid halide perovski...
Figure 2.53 Representative load-penetration depth plots for nanoindentation ...
Figure 2.54 (a) Pressure-dependent molecular volume (
V
/
Z
) in phases II, IV, ...
Figure 2.55 (a) Illustration of the setup for measuring thermal conductivity...
Figure 2.56 Simulated electrocaloric effect of MAPbI
3
, where (a) shows the a...
Figure 2.57 (a) Adiabatic temperature change in response to a hydrostatic co...
Chapter 3
Scheme 3.1 Coordination modes of HCOO
−
group in formate HOIP: syn–anti...
Figure 3.1 The structures of a selection of possible A-site cations used in ...
Figure 3.2 The structures of [NH
4
][Cd(HCOO)
3
] (a; orthorhombic,
Pna
2
1
) and [...
Figure 3.3 The crystal structures of six prototypical formate HOIPs at ambie...
Figure 3.4 The structures of two prototypical formate HOIPs: (a) [GUA][Zn(HC...
Figure 3.5 The structures of two prototypical formate double perovskites: (a...
Figure 3.6 Order–disorder phase transition between the high- and low-tempera...
Figure 3.7 Order–disorder phase transition between the high- and low-tempera...
Figure 3.8 Order–disorder phase transition between the high- and low-tempera...
Figure 3.9 Plot of
χ
m
T
versus
T
for four formate perovskites in an appl...
Figure 3.10 One Cu formate chain in which Cu
2+
ions are connected by sho...
Figure 3.11 Plots of
χ
m
T
versus
T
for [MA][Mn
1−
x
Zn
x
(HCOO)
3
] (
x
= ...
Figure 3.12 (a) Close-up view of the crystal structure of [DMA][Cu(HCOO)
3
] a...
Figure 3.13
M
, d
M
/d
H
, and
χ
′ as a function of
H
for [MA][Mn(HCOO)
3
], [E...
Figure 3.14 (a) d
M
/d
H
versus
H
plots for [HAZ][Mn(HCOO)
3
] (black) and [HAZ][...
Figure 3.15 Long-range canted anti-ferromagnetic order and isolated single-i...
Figure 3.16 The ring-pucker angle (
θ
) of AZE as a function of temperatu...
Figure 3.17 (a) The dielectric constant (
ε
1
) of [AZE][Zn(HCOO)
3
] as a f...
Figure 3.18 Dielectric constant (
ε
′
) plotted against
T
for compou...
Figure 3.19 The cavities at 290 K in (a) compounds [(HAZ)][Mn(HCOO)
3
] and (b...
Figure 3.20 (a) Synchrotron powder X-ray patterns of [DMA][Zn(HCOO)
3
] collec...
Figure 3.21 Ferroelectric phase transitions between the LT and HT structures...
Figure 3.22 (a) The polarization–field strength (
P
–
E
) hysteresis loops colle...
Figure 3.23 (a) Hydrogen bonding in the centrosymmetric
Pnan
phase of [GUA][...
Figure 3.24 Coupling of the Jahn–Teller modes to A-site through hydrogen bon...
Figure 3.25 Variation of the total energy as a function of the different dis...
Figure 3.26 Top panel: Variation of total energy as a function of the normal...
Figure 3.27 Epitaxial strain dependence of polarization in the lowest energy...
Figure 3.28 Crystal structure of framework [AZE][Mn(HCOO)
3
]. (a, b) The conf...
Figure 3.29 (a) Variations of unit cell parameters
a
,
b
,
c
, and
β
angle...
Figure 3.30 Temperature dependencies of (a)
f
2
and (b)
Q
−1
, from fittin...
Figure 3.31 (a) Low-temperature values of
f
2
(crosses) and
Q
−1
(open c...
Figure 3.32 (a) The inverse magnetic susceptibility as a function of tempera...
Figure 3.33 (a) Temperature-dependent magnetization with an applied field of...
Figure 3.34 (a) The
ab
-plane magnetization along [110] as a function of temp...
Figure 3.35 (a) Temperature dependence of electrical polarization Δ
P
and tem...
Figure 3.36 The electric-magneto-optical Kerr effect in [GUA][Cr(HCOO)
3
]. Th...
Figure 3.37 (a) Representative
P–h
curves of [DMA][M(HCOO)
3
] (M = Mn
2+
...
Figure 3.38 Crystal structures of [GUA][Zn(HCOO)
3
] and [GUA][Cu(HCOO)
3
]: (a,...
Figure 3.39 (a) Representative load–indentation displacement (
P–h
) plo...
Figure 3.40 Crystal structures of [GUA][Mn(HCOO)
3
] (a) and [AZE][Mn(HCOO)
3
] ...
Figure 3.41 Nanoindentation results obtained from the {010}, {101}, and
pl...
Figure 3.42 Schematic illustration for calculating the hydrogen-bonding ener...
Figure 3.43 (a) Elastic moduli (
E
) and (b) hardness properties of formate pe...
Figure 3.44 (a) The framework strut length
r
(M⋯M distance) and the intrafra...
Figure 3.45 XBU thermal expansion properties as a function of metal cation s...
Figure 3.46 Thermal expansion behaviour and mechanisms of [GUA][Zn(HCOO)
3
] a...
Figure 3.47 Equivalent isotropic atomic displacement parameters (
U
iso
) for z...
Figure 3.48 (a, b) The hinge-strut-like structure models for the frameworks ...
Figure 3.49 Crystal structure of [DMA][Mg(HCOO)
3
] phases in corresponding pr...
Figure 3.50 Molecular volume
V
/
Z
in the high- and low-temperature phases of ...
Figure 3.51 Pressure-induced calorimetric effects in [DMA][Mg(HCOO)
3
]. (a) E...
Figure 3.52 The barocaloric effect of [DMA][Mg(HCOO)
3
]: (a) entropy change Δ
Chapter 4
Figure 4.1 The structures of a selection of possible A-site organic amine ca...
Figure 4.2 Coordination modes of the azide group in azide HOIP: (a) Trans-EE...
Figure 4.3 The crystal structures of some prototypical azide HOIPs: (a) [DMA...
Figure 4.4 The framework structures of a family of manganese azide HOIPs: (a...
Figure 4.5 The crystal structures of two prototypical azide double perovskit...
Figure 4.6 Phase transition between the high- and low-temperature structures...
Figure 4.7 (a) and (b) The HT (270 K) and LT (260 K) structures of [MA][Mn(N
Figure 4.8 Temperature-dependent ƒ
2
(a) and
Q
−1
(b) from fitting sever...
Figure 4.9 The contribution of phonon modes with different energies to the v...
Figure 4.10 The temperature-dependent vibrational entropy (
S
Vib
) and Gibbs f...
Figure 4.11 The decomposed phonon contribution of the A-site (green), B-site...
Figure 4.12 The physical model of the mode energy dependencies of DOS for th...
Figure 4.13 Plots of
X
m
versus
T
(a) and
X
m
versus
T
(b) for [TMA][Mn(N
3
)
3
]....
Figure 4.14 Magnetic susceptibility (a) and magnetic hysteresis loops (b) fo...
Figure 4.15 Structural phase transitions of [TMA][Cd(N
3
)
3
]: (a) 220 K; (b) 3...
Figure 4.16 Structural phase transitions of [TMA]
2
[BB′(N
3
)
6
] (B = Cr
3+
a...
Figure 4.17 Dielectric permittivities as a function of temperature of [TMA]
2
Figure 4.18 The LT (a) and HT (b) structures of [DMA][Cd(N
3
)
3
].
Note
: The DM...
Figure 4.19 The real (a) and imaginary (b) parts of the dielectric constant ...
Figure 4.20 Rotation models for the DMA cation in the LT (model A) and HT ph...
Figure 4.21 The Mn⋯Mn distances (Å) and Mn⋯Mn⋯Mn angles (
°
) of the pseu...
Figure 4.22 The real and imaginary parts of the dielectric constant as a fun...
Figure 4.23 The schematic illustration of DFT calculations approach of the [...
Figure 4.24 The DFT calculation strategy for evaluating anti-ferroelectricit...
Figure 4.25 The temperature-dependent structural changes of the azide groups...
Figure 4.26 Representative load–penetration depth (
P
–
h
) curves for (100) and...
Figure 4.27 Framework structure of [DMA][Mn(N
3
)
3
] normal to (100) and (001) ...
Chapter 5
Figure 5.1 The dca
−
group with a
μ
1.5
-coordination mode.
Figure 5.2 Possible A-site organic cations that form dca HOIPs. Colour schem...
Figure 5.3 [Am][Mn(dca)
3
] perovskites with 3D α-polonium (pseudo-cubic) type...
Figure 5.4 Structures of [PTEP][Cd(dca)
3
] at phase I (a) and phase II (b). (...
Figure 5.5 Phase transition of [TPrA][Mn(dca)
3
] from LT (a) to HT phase (b) ...
Figure 5.6 DSC runs of [TPrA][Mn(dca)
3
] at different pressures. Phase transi...
Figure 5.7 Temperature-dependent dielectric constant (
ε
′
r
) of [TP...
Figure 5.8 Temperature-dependent dielectric constant (
ε
′
r
) of [TP...
Figure 5.9 Dielectric constant (
ε
′
r
) of [PTEP][Cd(dca)
3
] through ...
Figure 5.10 Temperature-dependent optical characterization of [PTEP][Cd(dca)
Figure 5.11 Temperature-dependent magnetic susceptibility plotted as
μ
e
...
Figure 5.12 Magnetic structure diagrams of [TPrA][Mn(dca)
3
] at low (
H
<
H
SF
)...
Figure 5.13 Typical nanoindentation
P–h
curves normal to {001} and {110...
Figure 5.14 Linear thermal expansion coefficients (
α
a
,
α
c
) and vol...
Figure 5.15 Barocaloric effect of [TPrA][Mn(dca)
3
]. (a) Isobaric entropy cha...
Chapter 6
Figure 6.1 The structures of a selection of possible A-site organic amine ca...
Figure 6.2 The crystal structures of some representative cyanide HOIPs. (a) ...
Figure 6.3 The crystal structures of [GUA]
2
[KFe(CN)
6
] (a) and [ACA]
2
[KFe(CN)
Figure 6.4 The crystal structures of [TMA]
2
[KCr(CN)
6
]. Colour schemes: sodiu...
Figure 6.5 Crystal structures of (HIM)
2
[KFe(CN)
6
] at the low-temperature (a,...
Figure 6.6 The crystal structures of (HIM)
2
[KCo(CN)
6
] at 293 K (a) and 93 K ...
Figure 6.7 Evolution of crystal structures of [GUA]
2
[KFe(CN)
6
] (a, 1γ) and [...
Figure 6.8 Structural phase transitions of [MA]
2
[KFe(CN)
6
], [DMA]
2
[KFe(CN)
6
]...
Figure 6.9 The motion models of [DMA]
2
[KCo(CN)
6
] at 180–200 K (I), 230–250 K...
Figure 6.10 DSC plots of [MA]
2
[K
1−
x
Rb
x
Co(CN)
6
] between 340 and 565 K (
Figure 6.11 Phase transition involving bond switching in [TrMNO]
2
[KFe(CN)
6
]....
Figure 6.12 Temperature-dependent SHG property of [TrMNO]
2
[KFe(CN)
6
].
Figure 6.13 The real part of dielectricity constant of a [HIM]
2
[KFe(CN)
6
] si...
Figure 6.14 (a) Temperature-dependent real part of dielectric constant for [...
Figure 6.15 Dielectric constants of [TrMA]
2
[KFe(CN)
6
] as a function of tempe...
Figure 6.16 Cycling switch of
ε′
between the low- and high-temper...
Figure 6.17 The real part of the dielectric constant (
ε
′) of [MA]
2
[K
1−x
...
Figure 6.18 Room temperature ferroelectric hysteresis loops of thin film of ...
Figure 6.19 Polarization reversal of the [(CH
3
)
3
NOH]
2
[KFe(CN)
6
] thin film wh...
Chapter 7
Figure 7.1 The molecular structure of the only available A-site cation, PPN
+
...
Figure 7.2 The structure of [PPN][M{Au(CN)
2
}
3
] HOIPs. (a) M = Ni or Co and (...
Figure 7.3 The unusual octahedral tilting of [PPN][Cd{Ag(CN)
2
}
3
]·3CH
3
CH
2
OH. ...
Figure 7.4 Short range cation–π and π–π interactions in [PPN][Cd{Au(CN)
2
}
3
]....
Figure 7.5 Temperature dependence of the effective magnetic moment of PPN{M[...
Chapter 8
Figure 8.1 Comparison of formate (a) and hypophosphite (b); the crystal stru...
Figure 8.2 The structures of a selection of possible A-site cations used in ...
Figure 8.3 The crystal structures of [FA][Mn(H
2
POO)
3
] (a), [DMA][Mn(H
2
POO)
3
]...
Figure 8.4 Temperature-dependent phase transition of hypophosphite HOIPs. Th...
Figure 8.5 Representative load–penetration depth (
P–h
) curves for (101...
Figure 8.6 Temperature-dependent magnetic susceptibilities of [FA][Mn(H
2
POO)
Figure 8.7 Different Mn–H
2
POO bonding geometries (a) and electronic spin den...
Chapter 9
Figure 9.1 The structures of a selection of possible A-site organic amine ca...
Figure 9.2 Representative structures of perchlorate HOIPs crystallized in di...
Figure 9.3 The structure of [HPZ][K(ClO
4
)
3
] in three different phases.
Figure 9.4 The structure of [PIP][Na(ClO
4
)
3
] in three different phases.
Figure 9.5 The evolution of unit cell volume as a function of pressure. The ...
Figure 9.6 Framework structure of [DABCO][K(ClO
4
)
3
] at 0 (a, b, g), 1.59 (c,...
Figure 9.7 3D and 2D representations of the Young's modulus
E
(a, b), Poisso...
Figure 9.8 (a) Temperature dependence of
ε
′ of [H
2
hpz][K(ClO
4
)
3
] measur...
Figure 9.9 Bar chart representation of detonation parameters calculated by E...
Figure 9.10 Bar chart representation of detonation parameters evaluated by D...
Figure 9.11 The molecular structures of possible A-site organic amine cation...
Figure 9.12 The perovskite structures of [DABCO][K(BF
4
)
3
] (a) and [PIP][Na(B...
Figure 9.13 DSC curves of [PIP][Na(BF
4
)
3
] (three cycles) measured between 30...
Figure 9.14 The ambient (a) and high-temperature (b) structures of [MDABCO][...
Figure 9.15 The real (a) and imaginary (b) parts of dielectric constant of [...
Figure 9.16 (a) The crystal structure of [PIP][(NH
4
)Cl
3
]·H
2
O. (b) Hydrogen b...
Figure 9.17 The structures of a selection of possible A-site cations used in...
Figure 9.18 The crystal structures of metal-free perovskites templated by di...
Figure 9.19 DFT-calculated electronic band structures and partial density of...
Figure 9.20 The packing diagrams of [MDABCO][NH
4
I
3
] in (a) the
room temperat
...
Figure 9.21 Photograph of [MDABCO]NH
4
I
3
crystal samples under (a) natural li...
Figure 9.22 Photoluminescence (a) and morphology (b) properties of 0.5% SnI
x
Figure 9.23 Ferroelectric properties of [MDABCO]NH
4
I
3
. (a) DSC measurements....
Figure 9.24 Piezoelectric force microscopy (PFM) data of [MDABCO]NH
4
I
3
. (a) ...
Figure 9.25 (a–c) Directional Young's modulus of MDABCO–NH
4
–Cl
3
, MDABCO–NH
4
–...
Figure 9.26 High-pressure and nanoindentation experiments of [MDABCO][(NH
4
)I
Figure 9.27 3D and 2D representations of Young's modulus (a) and (d), shear ...
Figure 9.28 (a) Pressure-dependent relative changes in length for the three ...
Guide
Cover
Table of Contents
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Hybrid Organic-Inorganic Perovskites
Wei Li
Alessandro Stroppa
Zhe-Ming Wang
Song Gao
Authors
Prof. Wei Li
Nankai University
School of Materials Science and
Engineering
38 Tongyan Road
300350 Tianjin
China
Dr. Alessandro Stroppa
CNR-SPIN
University of L'Aquila
c/o Department of Physical and
Chemical Science
Via Vetoio
67100 Coppito (AQ)
Italy
Prof. Zhe-Ming Wang
Peking University
College of Chemistry and Molecular
Engineering
Chengfu Road 292
100871 Beijing
China
Prof. Song Gao
Peking University
College of Chemistry and Molecular
Engineering
ChengFu Road 292
100871 Beijing
China
and
South China University of Technology
School of Chemistry and Chemical
Engineering
381 Wushan Road
510640 Guangzhou
China
Cover Images:
Hybrid Organic-Inorganic
Courtesy of Wei Li, Abstract alter
hintergrund © Pexels/9151
Bilder/Pixabay
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Preface
Hybrid organic–inorganic perovskites have attracted substantial interest during the past decade because of their chemical variability, structural diversity, and remarkable physical properties. However, to date, there has been no book that covers the synthesis, structures, and functionalities of these fascinating materials. This important book, by Wei Li, Alessandro Stroppa, Zhe-Ming Wang, and Song Gao, who are international leaders in the field, fills this gap by summarizing the recent advances in all the known 3D hybrid perovskite subclasses, which include halides, azides, formates, hypophosphites, dicyanamides, cyanides, dicyanometallates, and even some metal-free systems. It also presents a comprehensive account of their intriguing physical properties, including photovoltaic and optoelectronic properties, magnetism, dielectricity, ferroelectricity, ferroelasticity, and multiferroicity. Such a timely book will give readers a comprehensive summary of the currently known 3D hybrid perovskites and also illustrate the many opportunities that lie beyond the popular halide materials.
Santa Barbara, May 2020
Anthony K. Cheetham, KBE FRS
Acknowledgements
This book was supported by the National Natural Science Foundation of China (grant nos 21571072, 21671008, 21975132, and 21991143) and the Fundamental Research Funds for the Central Universities (no. 63196006). The authors are also grateful to Nankai University, CNR-SPIN, Peking University, and South China University of Technology for their financial support.
1Introduction to Hybrid Organic–Inorganic Perovskites
1.1 Perovskite Oxides
Perovskite is a calcium titanium oxide mineral, which has the chemical formula of CaTiO3. It was discovered in 1839 by the Prussian mineralogist Gustav Rose in a piece of skarn collected from the Ural Mountains and named in honour of the Russian Count, Lev A. Perovskiy [1]. Nowadays, perovskites broadly denote any materials that have the same type of structure as CaTiO3, and their general chemical formula can be expressed as ABX3 [2]. The A and B represent two metal ions that have different ionic radii, and the X denotes an anion that is six-coordinated to the B-site. Adjacent BX6 octahedra are three dimensionally linked via sharing their corners to generate a framework structure in which the A-site counterbalancing cations are located in the framework cavities (Figure 1.1). The perovskite structure can also be considered as a cubic close-packed system in which the A- and X-sites are stacked in a cubic-close-packed manner along the body-diagonal direction.
Perovskite oxides have diverse compositions, which can accommodate a great deal of elements in the periodic table, and the corresponding chemical variations enable many physical properties that have important industrial applications [3]. Perovskite materials were only limited to applications as pigments initially; however, the surge of military need for ferroelectric materials during the 1940s led to the invention of BaTiO3 and the start of the electronic era of perovskites [4]. The crystal structure of BaTiO3 was solved by Helen D. Megaw in 1945, and this seminal work initiated the fundamental understanding of structural evolution and associated properties of synthetic perovskite oxides [5]. As illustrated in Figure 1.2a, the B-site Ti4+ displaces from the centre of TiO6 in the ambient trigonal phase of BaTiO3 (R3m), which induces the occurrence of spontaneous polarization and therefore ferroelectric ordering. BaTiO3 is one of the most commonly used ferroelectric ceramics in a variety of industrial fields nowadays. Research in 1950s led to the invention of another important perovskite ceramic, lead zirconate titanate (PbZrxTi1−xO3, PZT, 0 < x < 1), which is a solid solution of PbZrO3 and PbTiO3 (Figure 1.2b) [6]. PZT shows a striking piezoelectric effect in addition to its intrinsic ferroelectricity and has been being widely utilized as transducers, capacitors, and actuators in industry. Lanthanum manganite (LaMnO3, Figure 1.2c) is another very important perovskite oxide, which exhibits multiple degrees of freedom induced by the substitution of La3+ by Sr2+ or Ca2+ on the A-site [7]. Such a doping introduces Mn3+ in addition to the original Mn4+ on the B-site, and these discrete magnetic ground states enable the colossal magnetoresistance effect, which has promising applications in memory devices. In addition to the singular electric or magnetic properties, bismuth ferrite (BiFeO3) can exhibit both ferroelectric and magnetic ordering at ambient conditions to give rise to multiferroicity promising for applications in spintronics [8]. Overall, the enormous chemical availability of perovskite oxides gives rise to their diverse magnetic and electronic properties and corresponding applications.
Figure 1.1 Structure of perovskite mineral, CaTiO3. (a) The pseudo-cubic unit and (b) the 3D framework structure.
Source: Sasaki et al. 1987 [30]. Reproduced with permission of International Union of Crystallography.
Figure 1.2 Structures of some prototypic perovskite oxides at ambient conditions. (a) BaTiO3, tetragonal, and P4mm.
Source: Megaw 2001 [5]. Reproduced with permission of Springer Nature;
(b) PbTiO3, tetragonal, and P4mm.
Source: Glazer and Mabud 1974 [6]. Reproduced with permission of International Union of Crystallography;
and (c) LaMnO3, orthorhombic, and Pnma.
Source: Norby et al. 1995 [7]. Reproduced with permission of Elsevier;
(d) BiFeO3, trigonal, R3c.
Source: Frank and Hans 1990 [8]. Reproduced with permission of International Union of Crystallography.
In terms of synthesis [3], polycrystalline perovskite oxides are normally prepared by high-temperature solid-state reactions by mixing oxide reactants. In this process, some toxic starting oxides, especially PbO, could vaporize during the long reaction time and the generated volatile substances would cause serious safety and environmental problems. To overcome this issue, sol–gel, hydrothermal, and microwave synthesis methods are used to prepare various perovskite oxides. For synthesizing perovskite thin films, which can be integrated into silicon circuits, costly physical vapour deposition and pulsed laser deposition methods are often required.
1.2 Evolution from Perovskite Oxides to Hybrid Organic–Inorganic Perovskites
The A-, B-, and X-sites of the perovskite architecture are not limited to metal cations and oxygen anions, and they can accommodate versatile compositions if the charge balance and lattice match can be maintained. Replacing the A- and/or X-site metal ions with organic amine cations and/or molecular bitopic linkers leads to a sub-class of perovskite materials, namely hybrid organic–inorganic perovskites (HOIPs, Figure 1.3) [9]. Specifically, by introducing the organic molecular cations on the A-site and bitopic inorganic single or molecular anion on the X-sites, several families of hybrid perovskites can be formed, which include halides, azides, cyanides, hypophosphites, and borohydrides [9]. For example, the assembly of methylammonium iodide (CH3NH3I) and lead iodide (PbI2) in hydroiodic acid gives rise to the formation of MAPbI3 (MA = methylammonium) with striking photovoltaic properties (Figure 1.3b) [10]. Additional introduction of bitopic organic molecular linkers on the X-site leads to several families of metal–organic perovskites, which include metal–formate and metal–dicyanamide perovskites with formate and dicyanamide group on the X-site, respectively. For example, mixing methylamine, manganese salt, and formic acid gives rise to magnetic [MA][Mn(HCOO)3], which has organic components on both the A- and X-sites [11].
Importantly, the incorporation of organic components in the HOIP structures gives them significantly different electronic nature and structural flexibility compared with their oxide counterparts. These unique features could enable striking properties and associated functionalities that are not available in perovskite oxides. In addition, the enormous structural diversity and chemical variability of HOIPs would be expected to enable versatile physical properties and open up huge opportunities for tuning functionalities via facile bottom-up synthesis.
Figure 1.3 Evolution from perovskite oxides to hybrid organic–inorganic perovskites. (a) Perovskite oxide, CaTiO3[30]; (b) hybrid perovskite with the organic A-site, [MA][PbI3] [10]; and (c) hybrid perovskite with the organic A- and X-site, [MA][Mn(HCOO)3] [11]. Colour schemes: C, black; N, blue, O, red; and H, grey.
Source: Li et al. 2017 [9]. Reproduced with permission of the Nature Publishing Group.
1.3 Classification and Chemical Variations of HOIPs
In terms of structure, hybrid perovskites can be categorized as several sub-classes, which include ABX3 perovskites, A2BB′X6 double perovskites, A3BX anti-perovskites, ABX3 hexagonal perovskites, and ABX3 post-perovskites. The B-site metal ions in many HOIPs are divalent, replacing them with mixed monovalent and trivalent metal ions leading to diverse compounds with the A2BB′X6 double-perovskite structure, which include halides, azides, cyanides, and formates. Figure 1.4a shows a typical example of hybrid double perovskites, [TMA]2[KSc(HCOO)6] (TMA = tetramethylammonium), in which both the K+ and Sc3+ ions are on the B-site [12]. Hybrid anti-perovskites have also been reported, although they are relatively rare. Known examples include a few halides [13, 14] and a family of ternary tetrathiafulvalenium salts (Figure 1.4b) [15]. In addition, there are many ABX3-type hexagonal perovskites, in which the BX6 octahedra exhibit a face-sharing mode to form a one-dimensional structure [16]. These hybrid hexagonal perovskites are mainly halides, and Figure 1.4c shows a typical example, [DABCOH2][KCl3] [16]. Furthermore, recent studies demonstrate two very rare examples of hybrid ABX3-type post-perovskites, (C5H13NCl)[M(dca)3] (C5H13NCl = chlorocholine, M2+ = Mn2+ and Cd2+, and dca = dicyanamide), in which adjacent M(dca)6 octahedra are connected to generate anionic layers by sharing their edges and corners two dimensionally and the charge balancing A-site organic cations are intercalated between adjacent layers [17].
Figure 1.4 Prototypical examples of hybrid organic–inorganic perovskites with double perovskite, anti-perovskite, hexagonal perovskite, and post-perovskite structures. (a) Double perovskite, [TMA]2[KSc(HCOO)6].
Source: Javier et al. 2015 [12]. Reproduced with permission of American Chemical Society;
(b) anti-perovskite, (TTF•)3[(X)(Mo6X14)] (TTF•+ = tetrathiafulvalenium; X = C1, Br, and I).
Source: Batail 1991 [15]. Reproduced with permission of John Wiley & Sons;
(c) hexagonal perovskite, [DABCOH2][KCl3].
Source: Paton and Harrison 2010 [16]. Reproduced with permission of John Wiley & Sons;
(d) post-perovskite, (C5H13NCl)[Mn(dca)3].
Source: Wang et al. 2019 [17]. Reproduced with permission of American Chemical Society.
1.4 Structure, Symmetry, and Property Features of HOIPs
1.4.1 General Trend
The enormous diversity in organic cations on the A-site, metal ions on the B-site, and bitopic linkers on the X-site offers various combinations of HOIPs, which lead to more than a hundred hybrid perovskites covering a large part of the periodic table. The possible A-site organic groups are summarized in Figure 1.5, which demonstrate that most of them are organic amine cations with monovalent charge [9]. However, there are some organic diamine cations that can also be suitable as the A-site. In addition, few other types of organic cations can also serve as the A-site; for example, triphenylsulfonium is able to template the dca perovskites [18]. In terms of the X-site, they are all monovalent and can be monoatomic ion, biatomic group, and multi-atomic linkers (Figure 1.5). These X-sites include inorganic halide ion (Cl−, Br−, and I−), cyanide ion (CN−), azide ion (N3−), dicynametallate ion ([Ag(CN)2]− and [Au(CN)2]−), borohydride ion (BH4−), and organic formate (HCOO−) and dicyanamide (dca−) groups. Moreover, some ABX3-type perchlorates and tetraborates can be topologically regarded as the perovskite-like compounds in which the perchlorate (ClO4−) and tetraborate (BF4−) serve as the B-site [19]. With respect to the B-site, most of them are divalent metal ions or mixed monovalent/trivalent metal ions, although few are monovalent metal ions because of the existence of organic diamine cations on the A-site. Interestingly, NH4+ can also serve as the B-site by octahedrally interacting with six halide ions to form metal-free perovskites with the templating organic diamine cations, [A][(NH4)X3] (A2+ = organic diamine cation, X− = Cl−, Br−, and I−) [20].
Figure 1.5 Structural diversity of the A-site and X-site ions of hybrid organic–inorganic perovskites. Colour schemes: N, blue; O, red; C, black; H, grey or light pink; Cl, purple or green; Br/I, purple; S, light yellow; P, yellow or purple; M = Ag or Au, yellow; B, turquiose; and F, pink.
The symmetries of HOIPs span all seven crystal systems, which are largely dependent on the size, shape, and nature of the A-site organic cations (Table 1.1). Specifically, organic amine cations with high symmetries (i.e. TMA) often lead to perovskite structures with high-symmetry space groups. In addition, the change of ordering state of the A-site organic amine cations can also result in symmetry alterations. For example, the switching from ordered to disordered states of MA in MAPbI3 upon heating induces the symmetry change from orthorhombic to tetragonal, then to cubic. Like their inorganic counterparts, HOIPs can also exhibit diverse physical properties depending on their distinct compositions, which have been summarized in Table 1.1 [9]. Specifically, perovskite halides show remarkable optoelectronic properties, which have been intensively researched in the last 10 years. Perovskite formates demonstrate versatile magnetic properties, ferroelectricity and multiferroicity, as well as dielectricity.
Perovskite azides exhibit diverse magnetic properties and interesting ferroelasticity. Perovskite cyanides display various dielectricity and unique ferroelectric ordering. Dicyanamide perovskites show extraordinary barocaloric effects and associated solid-state cooling potential, as well as significant thermal expansion. All these striking properties of HOIPs are extensively discussed in the following chapters.
1.4.2 Ion Radius Matchability and Tolerance Factor
There are abundant variabilities of the A-, B-, and X-sites, and how to evaluate their matchability is a critical issue. According to the established criterion in perovskite oxides, the metric ratio of different ionic sizes, which can be tolerated by the perovskite lattice, is expressed by the Goldschmidt tolerance factor (TF, t) [21]. As the A-site and/or X-site in the HOIPs are not spherical ions but molecular groups, the t was adjusted to the following formula [22]:
where rB represents the radius of the B-site metal ion, and rAeff, rXeff, and hXeff stand for the effective radius of the A-site molecular group, the effective radius of the X-site molecular group, and the effective height of the X-site molecular group, respectively. As can be seen in Table 1.1, the calculations of TFs by summarizing all available A-site, B-site, and X-sites of known HOIPs demonstrate that most of their TF span is between ∼0.8 and ∼1.0. These results approximate those of conventional perovskite oxides and therefore indicate that such a semi-empirical rule can be extended to the hybrid systems. In other words, the lattice matchability and packing density primarily determine the formation of HOIPs. More importantly, this simple way can be facilely utilized to design new HOIPs, in which the rationally selected compositions with size compatibility can lead to desired functionalities. An expanded study of all possible A-site amine cations, B-site metal ions, and X-site anions across the periodic table reveals that several hundreds of HOIPs were yet to be discovered [23]. Following successive experimental discoveries of HOIPs with new physical properties have indeed demonstrated the validation of this powerful tool in synthesizing new functional HOIPs. For example, replacing toxic lead metal ion by mixed mono- and trivalent metal ions with benign nature keeps the size compatibility, and the obtained hybrid lead-free perovskite opens the possibility for addressing the environmental concern required for future industrial applications [24]. Nevertheless, special caution needs to be taken into account because such a simple metric is unable to fully reflect the lattice energetics and hence structure stability because of its empirical limitation.
Table 1.1 Summary of the chemical variabilities, crystal symmetries, and physical properties of HOIPs [9].
HOIPs
A-site
B-site
X-site
Symmetry
TFs
Physical properties
Halides
MA, FA
Pb
2+
, Sn
2+
, Ge
2+
Cl
−
, Br
−
, I
−
Orthorhombic, trigonal, tetragonal, cubic
∼0.912–1.142
Semiconductivity, photovoltaics, laser physics, light-emitting diodes, mechanical properties
MA
K
+
/Bi
3+
, Tl
+
/Bi
3+
a
∼0.906–0.923
b
PIP, DABCO
K
+
, Cs
+
, Rb
+
Cl
−
Monoclinic, orthorhombic, trigonal
∼0.922–1.037
Formates
K
+
, Rb, Cs
+
, NH
4
+
, MA, FA, GUA, EA, DMA, AZE, HIM, HAZ, MHy
Mg
2+
, Mn
2+
, Fe
2+
, Co
2+
, Ni
2+
, Cu
2+
, Zn
2+
, Cd
2+
HCOO
−
Monoclinic, orthorhombic, trigonal, tetragonal
∼0.784–1.001
c)
Magnetism, dielectricity, ferroelectricity, ferroelasticity, multiferroicity, mechanical properties
MA, TMA, DMA, EA, HAZ, GUA, TMA
Na
+
/Cr
3+
, Na
+
/Al
3+
, Na
+
/Fe
3+
, K
+
/Sc
3+
, Cu
2+
/Mn
2+
a
HCOO
−
Monoclinic, triclinic, trigonal
∼0.897–1.040
b)
Azides
MA, DMA, TEA, TrMA, TMA, CPA
Mn
2+
, Cd
2+
, Cu
2+
, Ca
2+
N
3
−
Triclinic, monoclinic, cubic
∼0.786–1.023
Magnetism, dielectricity, ferroelasticity
TMA
Na
+
/Cr
3+
, Na
+
/Fe
3+
, K
+
/Fe
3+
, K
+
/Cr
3+
a
∼0.934–1.008
b)
Dicyanamides
BPEA, BPTA, SPh
3
, TPrA
d)
Mn
2+
, Co
2+
, Cd
2+
, Fe
2+
, Ni
2+
[N(CN)
2
]
−
Monoclinic, orthorhombic, tetragonal
∼1.142–1.166
Magnetism, dielectricity, non-linear optical, spin canted, barocaloric
Dicyanometallates
PPN
Cd
2+
[Ag(CN)
2
]
−
Monoclinic, trigonal, cubic
∼1.033–1.141
d)
Magnetism
Mn
2+
, Co
2+
, Ni
2+
, Cd
2+
[Au(CN)
2
]
−
Cyanides
HIM, DMA, MA, TMA, TrMA, GUA, TEMA, ACA, TrMNO
K
+
/Fe
3+
, K
+
/Co
3+
, K
+
/Cr
3+
, Na
+
/Co
3+
, Na
+
/Fe
3+
, Rb
+
/Fe
3+
, Rb
+
/Co
3+
, Rb
+
/Cr
3+
, Cs
+
/Cr
3+
, Tl
+
/Cr
3+
, Tl
+
/Fe
3+
a)
CN
−
Triclinic, monoclinic, cubic, tetragonal
∼0.840–1.031
b)
Dielectricity, ferroelectricity
Borohydrides
MA
Ca
2+
BH
4
−
e
Cubic
∼0.980
Hydrogen storage
Hypophosphites
FA, GUA, HIM, TRZ, DMA, DABCO
Mn
2+
H
2
PO
2
−
Monoclinic, orthorhombic, triclinic, trigonal
∼0.860−0.910
Magnetism
Perchlorates
PIP, H
2
hpz, DABCO, ODABCO
K
+
, Na
+
, Rb
+
ClO
4
−
Orthorhombic, monoclinic, cubic
∼0.914–1.015
Dielectricity, high-energetic
Tetrafluoroborates
PIP, DABCO
K
+
, Na
+
BF
4
−
Trigonal, tetragonal, cubic
∼0.913–1.050
Dielectricity
Metal-free perovskites
PIP, DABCO, ODABCO,
rac
-2MP,
R
-,
S
-,
rac
-3AP,
R-
,
S-
,
rac
-3AQ
NH
4
+
Cl
−
, Br
−
, I
−
Monoclinic, orthorhombic, trigonal, cubic
∼0.870–1.000
High-energy, ferroelectricity, photoluminescence
ClO
4
−
BF
4
−
ReO
4
−
HOIPs, hybrid organic–inorganic perovskites; TFs, tolerance factors.
a) Mixed B-sites in hybrid double perovskites.
b) The TFs of hybrid double perovskites, A2BB′X6, were calculated using the adapted formula t = (rAeff + rXeff)/√2(rB/2 + rB′/2 + 0.5 hXeff). rAeff = rmass + rion, where rmass is defined as the distance between the centre of the mass of the A-site organic molecule ion and the atom with the largest distance to the centre of mass (excluding hydrogen atoms), and rion is the corresponding ionic radius of the aforementioned atom. rXeff can be defined in a similar way as rAeff.
c) The unique tolerance factors of KCo(HCOO)3, CsCo(HCOO)3 and [NH4][Cd(HCOO)3], which lie in the range ∼0.620 to 0.700, are not presented in the table owing to the special anti–syn coordination mode of the formate linker.
d) Since the BPEA, BPTA, and SPh3 cations are larger than the pseudo-cubic cavity, the relevant TFs were not able to be calculated.
e) The molecular structure of BH4− is not listed in the table because of the structural unavailability of [MA][Ca(BH4)3].
1.4.3 Phase Transitions
As one of the most studied class of materials, perovskites exhibit almost all known physical properties. Importantly, many of these phenomena, such as ferroelectricity and ferromagnetism, arise from their structural phase transitions. The ideal perovskite has a very simple cubic Oh symmetry and is in a space group. This parent high-symmetry aristotype architecture can evolve into a number of low-symmetry structures upon external stimuli, such as temperature and pressure. For conventional perovskites, their transitions are primarily driven by the displacement of the A- and/or B-site and the tilting of the BX6 octahedral units. According to these two primary driving forces, Glazer and some others developed an appropriate group theoretical analysis to classify the symmetry breaking and phase transitions of inorganic perovskites [25, 26]. Through this approach, structure variations and the underlying mechanisms could be well defined, which could give a fairly powerful guide to experimentalists.
In terms of HOIPs, their phase transition mechanisms are complicated because of the existence of molecular ions on the A- and/or X-sites compared with their conventional counterparts. For hybrid perovskite halides, their X-sites are still monatomic anions; therefore, their octahedral tilting modes are reminiscent with the scenarios in oxide perovskites. However, the octahedra are not corner-shared any more when the X-site becomes a diatomic or multi-atomic linker, which significantly complicates the structural transition mechanisms. As expected, the long and large X-sites in HOIPs could lead to additional structural freedom for the octahedra and A-site organic amine cations to distort and shift. For example, neighbouring octahedra can distort along the same direction in some azide perovskites, and such an unusual octahedral tilting is impossible to occur in conventional perovskites [27]. Nevertheless, in most HOIPs, the octahedral tilting modes resemble those in oxides because the X-site molecular linkers are fairly rigid, which do not allow special rotation of adjacent octahedra.
Compared with the conventional perovskites, the displacements of the A- and B-sites in HOIPs are broadly similar, which usually involve the off-centre shift. However, the existence of organic molecular groups on the A-site complicates the situation as additional bonding interactions, such as hydrogen bonding and van de Waals forces, have to be taken into account. Such additional structural degrees of freedom often significantly affect the phase transition scenarios. Moreover, the A- and/or X-sites can also show dynamic motions, which involve significant entropic effect and hence being a strong phase transition driving force. The dynamic movement over different sites of the molecular group (including both the A- and X-sites) is defined as disorder, and many phase transitions of HOIPs are primarily driven by such an order–disorder process because of its aforementioned energetic effect. Notably, such an order–disorder process often involves alterations of hydrogen bonding and dispersion forces between the A-site and anionic perovskite framework, which could synergistically influence the symmetry breaking process [28]. Figure 1.6 shows the phase transition of [AZE][Cu(HCOO)3] (AZE = azetidinium), as a typical example to showcase the synergistic mechanism. For the high-temperature Pnma phase, the AZE group exhibits a planar configuration with very large atomic displacement parameter of the side C2 atom (indicating a possible disorder of AZE at two sites over the N1–C1–C3 plane) and CuO6 octahedra show a tilting system of a−b+a−. Upon cooling, the structure evolves into the low-temperature P21/c phase in which the AZE is fully ordered and the CuO6 tilting becomes to a−b+c−. During this symmetry breaking process, the order–disorder of AZE is the main driving force, and the associated hydrogen bonding changes also play a role. This kind of orthorhombic Pnma to monoclinic P21/c transition is very rare as it requires the uncommon X-point modes in the Brillouin zone (while most transitions in conventional perovskites only involve the M- and R-point modes). Overall, the complex cooperation of various driving forces including displacement, octahedral tilting, and order–disorder leads to far more complicated phase transition mechanisms in HOIPs, in marked contrast to their inorganic counterparts [9].
Figure 1.6 Phase transition mechanism in [AZE][Cu(HCOO)3]. Colour schemes: N, blue; O, red; C, black; H, grey; and Cu, cyan.
Source: Zhou et al. 2011 [31]. Reproduced with permission of John Wiley & Sons.
More importantly, some special A-site organic amine cations are intrinsically polar so that bulk electric ordering could be obtained if they align in an ordered way through occurrence of phase transitions. This phenomenon is in marked difference to the displacive origin of electric ordering responsible for perovskite oxides. In addition, the alterations of hydrogen bonding and dispersion forces across phase transition play an important role in achieving such an ordered electric state. As expected, the obtained ferroelectric or anti-ferroelectric ordering strongly depends on the dipole moments carried by the A-site cations, along with other cooperative influences. Furthermore, the intimate cooperation of different bonding interactions from all sites in the structures of HOIPs during the symmetry breaking process could lead to ferroelasticity, multiferroicity, and many other novel properties, which are not possible in their conventional counterparts. These multiple bonding forces also play a pivotal role in modulating physical properties of HOIPs, which include magnetism, conductivity, and dielectricity [9, 29].
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2Hybrid Halide Perovskites
2.1 Synthesis and Chemical Diversity
The halides (X− = Cl−, Br−, and I−) are bridging ions with effective lengths of about 3.62–4.40 Å [1], which enable them to function as suitable X-sites to coordinate with appropriate B-site metal ions to form the perovskite architecture in aid of templating organic amine cations. Accordingly, about 25 perovskite-like metal–halide frameworks have been synthesized using several different organic amine cations under simple solution conditions (Figure 2.1 and Table 2.1) [18–20]. When the B-site cation is limited to the group IVA metals Pb and Sn, with divalent charge, the resulting BX3− perovskite frameworks can only accommodate the smallest monovalent organic cations, such as methylammonium (MA) and formamidinium (FA), according to the Goldschmidt tolerance factors (TFs) [1]. Larger moieties at the A-site result in layered structures, which are not discussed here [20].
In terms of [MA][PbX3] (X = Cl, Br, and I), there are several methods for preparing the compounds, and the most well-known compound is according to an early work reported by Poglitsch and Weber [2, 21]. Specifically, lead acetate is dissolved in relevant hydrochloric, hydrobromic, or hydroiodic acid solutions and then gets heated to 373 K in an oil bath. Separately, methylamine is added to the acid solutions to form relevant MA salts at 273 K. Then, the cold MA halide solutions are added to the hot lead acetate solution and cooled for about two hours to 319 K, giving rise to black crystalline precipitates with yield over 70% after filtration and drying. The synthesis of [FA][PbX3] (X = Cl, Br, and I) requires an inert atmosphere [18, 19]. The aqueous H3PO2 solution and hydrochloric/hydrobromic/hydroiodic acid solution are mixed in the nitrogen atmosphere, and then, PbX2 salt is dissolved in the mixture upon heating to form a clear solution. HC(NH2)2X solid is added to this clear solution and heated. The solution is concentrated to half volumetrically, and slow cooling gives crystal precipitates with yield over 70%.
As lead is toxic, a search has begun for more eco-friendly perovskite halides. [MA][SnX3] and [FA][SnX3] (X = Cl, Br, and I) are natural replacements of lead halides [4–6, 8, 9]. They are synthesized in a similar way to lead compounds but requiring an inert atmosphere. Taking the iodide compounds as an example, [MA][SnI3] and [FA][SnI3] are prepared from the mixed solution of hydrochloric/hydrobromic/hydroiodic acid solution, aqueous H3PO2, PbI2, and HC(NH2)2I salts in inert gas [4]. Notably, these [MA][SnI3] and [FA][SnI3] crystals decompose quite rapidly upon exposing to the atmosphere and have to be stored in protected inert atmosphere. In addition, perovskite halides incorporating benign Ge have also been successfully prepared, which include MAGeI3, FAGeI3, and [ACA][GeI3] (ACA, acetamidinium) [7]. The synthesis is reminiscent of the tin iodides by using GeI4 and GeO2 as the metal source. It is worth mentioning that the strong stereochemical influence of the lone pair s-orbitals of Ge2+ gives rise to much distorted GeI6 octahedra in these materials, which are composed of three typical and three elongated Ge—I bonds. As a result, these germanium halide perovskites are more easily oxidized than lead and tin analogues, further indicating that this strategy is probably impractical.
Figure 2.1 The structures of a selection of possible A-site cations used in halide HOIPs. Colour schemes: carbon, black; nitrogen, blue; hydrogen, light grey; and halogen, purple.
Another approach is to construct double perovskites through substitution of the divalent metals (Pb2+, Sn2+, or Ge2+) with a combination of monovalent and trivalent metals. This has been realized in hybrid perovskites templated by MA cations, and the synthesis of these double perovskite halides is broadly similar to their single metal analogues, apart from using combined mono- and trivalent metal sources. The first success is [(MA)2][KBiCl6], which was prepared in single-crystal form through the hydrothermal method in a stainless steel Parr autoclave using stoichiometric MA chloride, potassium, and bismuth chloride in hydrochloric acid solution [14]. The inclusion of strongly ionic K+ ions in this compound leads to a wide indirect bandgap of about 3.0 eV, which excludes any promising application in optoelectronics. In this regard, monovalent transition metal ions were considered as replacements. To obtain the desirable bandgaps for photovoltaic applications, isoelectronic double perovskites are ideal candidates. [(MA)2][TlBiBr6] is isoelectronic to the high MAPbI3, and it was synthesized in single-crystal form through the hydrothermal method using stoichiometric MA bromide, thallium acetate, and bismuth bromide in hydrobromic acid solution [15]. Notably, although [(MA)2][TlBiBr6] is isoelectronic with MAPbBr3, the toxicity of Tl
