79 research outputs found
Cova de Can Sadurní, la transformació d’un jaciment. L’episodi sepulcral del neolític postcardial
The
present study deals with the structural characterization and classification
of the novel compounds <b>1</b>–<b>8</b> into perovskite
subclasses and proceeds in extracting the structure–band gap
relationships between them. The compounds were obtained from the employment
of small, 3–5-atom-wide organic ammonium ions seeking to discover
new perovskite-like compounds. The compounds reported here adopt unique
or rare structure types akin to the prototype structure perovskite.
When trimethylammonium (TMA) was employed, we obtained TMASnI<sub>3</sub> (<b>1</b>), which is our reference compound for a “perovskitoid”
structure of face-sharing octahedra. The compounds EASnI<sub>3</sub> (<b>2b</b>), GASnI<sub>3</sub> (<b>3a</b>), ACASnI<sub>3</sub> (<b>4</b>), and IMSnI<sub>3</sub> (<b>5</b>)
obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium
(ACA), and imidazolium (IM) cations, respectively, represent the first
entries of the so-called “hexagonal perovskite polytypes”
in the hybrid halide perovskite library. The hexagonal perovskites
define a new family of hybrid halide perovskites with a crystal structure
that emerges from a blend of corner- and face-sharing octahedral connections
in various proportions. The small organic cations can also stabilize
a second structural type characterized by a crystal lattice with reduced
dimensionality. These compounds include the two-dimensional (2D) perovskites
GA<sub>2</sub>SnI<sub>4</sub> (<b>3b</b>) and IPA<sub>3</sub>Sn<sub>2</sub>I<sub>7</sub> (<b>6b</b>) and the one-dimensional
(1D) perovskite IPA<sub>3</sub>SnI<sub>5</sub> (<b>6a</b>).
The known 2D perovskite BA<sub>2</sub>MASn<sub>2</sub>I<sub>7</sub> (<b>7</b>) and the related all-inorganic 1D perovskite “RbSnF<sub>2</sub>I” (<b>8</b>) have also been synthesized. All
compounds have been identified as medium-to-wide-band-gap semiconductors
in the range of <i>E</i><sub>g</sub> = 1.90–2.40
eV, with the band gap progressively decreasing with increased corner-sharing
functionality and increased torsion angle in the octahedral connectivity
Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties
A broad organic–inorganic
series of hybrid metal iodide perovskites with the general formulation
AMI<sub>3</sub>, where A is the methylammonium (CH<sub>3</sub>NH<sub>3</sub><sup>+</sup>) or formamidinium (HC(NH<sub>2</sub>)<sub>2</sub><sup>+</sup>) cation and M is Sn (<b>1</b> and <b>2</b>) or Pb (<b>3</b> and <b>4</b>) are reported. The compounds
have been prepared through a variety of synthetic approaches, and
the nature of the resulting materials is discussed in terms of their
thermal stability and optical and electronic properties. We find that
the chemical and physical properties of these materials strongly depend
on the preparation method. Single crystal X-ray diffraction analysis
of <b>1</b>–<b>4</b> classifies the compounds in
the perovskite structural family. Structural phase transitions were
observed and investigated by temperature-dependent single crystal
X-ray diffraction in the 100–400 K range. The charge transport
properties of the materials are discussed in conjunction with diffuse
reflectance studies in the mid-IR region that display characteristic
absorption features. Temperature-dependent studies show a strong dependence
of the resistivity as a function of the crystal structure. Optical
absorption measurements indicate that <b>1</b>–<b>4</b> behave as direct-gap semiconductors with energy band gaps
distributed in the range of 1.25–1.75 eV. The compounds exhibit
an intense near-IR photoluminescence (PL) emission in the 700–1000
nm range (1.1–1.7 eV) at room temperature. We show that solid
solutions between the Sn and Pb compounds are readily accessible throughout
the composition range. The optical properties such as energy band
gap, emission intensity, and wavelength can be readily controlled
as we show for the isostructural series of solid solutions CH<sub>3</sub>NH<sub>3</sub>Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>I<sub>3</sub> (<b>5</b>). The charge
transport type in these materials was characterized by Seebeck coefficient
and Hall-effect measurements. The compounds behave as <i>p</i>- or <i>n</i>-type semiconductors depending on the preparation
method. The samples with the lowest carrier concentration are prepared
from solution and are <i>n</i>-type; <i>p</i>-type
samples can be obtained through solid state reactions exposed in air
in a controllable manner. In the case of Sn compounds, there is a
facile tendency toward oxidation which causes the materials to be
doped with Sn<sup>4+</sup> and thus behave as <i>p</i>-type
semiconductors displaying metal-like conductivity. The compounds appear
to possess very high estimated electron and hole mobilities that exceed
2000 cm<sup>2</sup>/(V s) and 300 cm<sup>2</sup>/(V s), respectively,
as shown in the case of CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub> (<b>1</b>). We also compare the properties of the title hybrid
materials with those of the “all-inorganic” CsSnI<sub>3</sub> and CsPbI<sub>3</sub> prepared using identical synthetic
methods
Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties
A broad organic–inorganic
series of hybrid metal iodide perovskites with the general formulation
AMI<sub>3</sub>, where A is the methylammonium (CH<sub>3</sub>NH<sub>3</sub><sup>+</sup>) or formamidinium (HC(NH<sub>2</sub>)<sub>2</sub><sup>+</sup>) cation and M is Sn (<b>1</b> and <b>2</b>) or Pb (<b>3</b> and <b>4</b>) are reported. The compounds
have been prepared through a variety of synthetic approaches, and
the nature of the resulting materials is discussed in terms of their
thermal stability and optical and electronic properties. We find that
the chemical and physical properties of these materials strongly depend
on the preparation method. Single crystal X-ray diffraction analysis
of <b>1</b>–<b>4</b> classifies the compounds in
the perovskite structural family. Structural phase transitions were
observed and investigated by temperature-dependent single crystal
X-ray diffraction in the 100–400 K range. The charge transport
properties of the materials are discussed in conjunction with diffuse
reflectance studies in the mid-IR region that display characteristic
absorption features. Temperature-dependent studies show a strong dependence
of the resistivity as a function of the crystal structure. Optical
absorption measurements indicate that <b>1</b>–<b>4</b> behave as direct-gap semiconductors with energy band gaps
distributed in the range of 1.25–1.75 eV. The compounds exhibit
an intense near-IR photoluminescence (PL) emission in the 700–1000
nm range (1.1–1.7 eV) at room temperature. We show that solid
solutions between the Sn and Pb compounds are readily accessible throughout
the composition range. The optical properties such as energy band
gap, emission intensity, and wavelength can be readily controlled
as we show for the isostructural series of solid solutions CH<sub>3</sub>NH<sub>3</sub>Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>I<sub>3</sub> (<b>5</b>). The charge
transport type in these materials was characterized by Seebeck coefficient
and Hall-effect measurements. The compounds behave as <i>p</i>- or <i>n</i>-type semiconductors depending on the preparation
method. The samples with the lowest carrier concentration are prepared
from solution and are <i>n</i>-type; <i>p</i>-type
samples can be obtained through solid state reactions exposed in air
in a controllable manner. In the case of Sn compounds, there is a
facile tendency toward oxidation which causes the materials to be
doped with Sn<sup>4+</sup> and thus behave as <i>p</i>-type
semiconductors displaying metal-like conductivity. The compounds appear
to possess very high estimated electron and hole mobilities that exceed
2000 cm<sup>2</sup>/(V s) and 300 cm<sup>2</sup>/(V s), respectively,
as shown in the case of CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub> (<b>1</b>). We also compare the properties of the title hybrid
materials with those of the “all-inorganic” CsSnI<sub>3</sub> and CsPbI<sub>3</sub> prepared using identical synthetic
methods
Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties
A broad organic–inorganic
series of hybrid metal iodide perovskites with the general formulation
AMI<sub>3</sub>, where A is the methylammonium (CH<sub>3</sub>NH<sub>3</sub><sup>+</sup>) or formamidinium (HC(NH<sub>2</sub>)<sub>2</sub><sup>+</sup>) cation and M is Sn (<b>1</b> and <b>2</b>) or Pb (<b>3</b> and <b>4</b>) are reported. The compounds
have been prepared through a variety of synthetic approaches, and
the nature of the resulting materials is discussed in terms of their
thermal stability and optical and electronic properties. We find that
the chemical and physical properties of these materials strongly depend
on the preparation method. Single crystal X-ray diffraction analysis
of <b>1</b>–<b>4</b> classifies the compounds in
the perovskite structural family. Structural phase transitions were
observed and investigated by temperature-dependent single crystal
X-ray diffraction in the 100–400 K range. The charge transport
properties of the materials are discussed in conjunction with diffuse
reflectance studies in the mid-IR region that display characteristic
absorption features. Temperature-dependent studies show a strong dependence
of the resistivity as a function of the crystal structure. Optical
absorption measurements indicate that <b>1</b>–<b>4</b> behave as direct-gap semiconductors with energy band gaps
distributed in the range of 1.25–1.75 eV. The compounds exhibit
an intense near-IR photoluminescence (PL) emission in the 700–1000
nm range (1.1–1.7 eV) at room temperature. We show that solid
solutions between the Sn and Pb compounds are readily accessible throughout
the composition range. The optical properties such as energy band
gap, emission intensity, and wavelength can be readily controlled
as we show for the isostructural series of solid solutions CH<sub>3</sub>NH<sub>3</sub>Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>I<sub>3</sub> (<b>5</b>). The charge
transport type in these materials was characterized by Seebeck coefficient
and Hall-effect measurements. The compounds behave as <i>p</i>- or <i>n</i>-type semiconductors depending on the preparation
method. The samples with the lowest carrier concentration are prepared
from solution and are <i>n</i>-type; <i>p</i>-type
samples can be obtained through solid state reactions exposed in air
in a controllable manner. In the case of Sn compounds, there is a
facile tendency toward oxidation which causes the materials to be
doped with Sn<sup>4+</sup> and thus behave as <i>p</i>-type
semiconductors displaying metal-like conductivity. The compounds appear
to possess very high estimated electron and hole mobilities that exceed
2000 cm<sup>2</sup>/(V s) and 300 cm<sup>2</sup>/(V s), respectively,
as shown in the case of CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub> (<b>1</b>). We also compare the properties of the title hybrid
materials with those of the “all-inorganic” CsSnI<sub>3</sub> and CsPbI<sub>3</sub> prepared using identical synthetic
methods
Semiconducting Tin and Lead Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-Infrared Photoluminescent Properties
A broad organic–inorganic
series of hybrid metal iodide perovskites with the general formulation
AMI<sub>3</sub>, where A is the methylammonium (CH<sub>3</sub>NH<sub>3</sub><sup>+</sup>) or formamidinium (HC(NH<sub>2</sub>)<sub>2</sub><sup>+</sup>) cation and M is Sn (<b>1</b> and <b>2</b>) or Pb (<b>3</b> and <b>4</b>) are reported. The compounds
have been prepared through a variety of synthetic approaches, and
the nature of the resulting materials is discussed in terms of their
thermal stability and optical and electronic properties. We find that
the chemical and physical properties of these materials strongly depend
on the preparation method. Single crystal X-ray diffraction analysis
of <b>1</b>–<b>4</b> classifies the compounds in
the perovskite structural family. Structural phase transitions were
observed and investigated by temperature-dependent single crystal
X-ray diffraction in the 100–400 K range. The charge transport
properties of the materials are discussed in conjunction with diffuse
reflectance studies in the mid-IR region that display characteristic
absorption features. Temperature-dependent studies show a strong dependence
of the resistivity as a function of the crystal structure. Optical
absorption measurements indicate that <b>1</b>–<b>4</b> behave as direct-gap semiconductors with energy band gaps
distributed in the range of 1.25–1.75 eV. The compounds exhibit
an intense near-IR photoluminescence (PL) emission in the 700–1000
nm range (1.1–1.7 eV) at room temperature. We show that solid
solutions between the Sn and Pb compounds are readily accessible throughout
the composition range. The optical properties such as energy band
gap, emission intensity, and wavelength can be readily controlled
as we show for the isostructural series of solid solutions CH<sub>3</sub>NH<sub>3</sub>Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>I<sub>3</sub> (<b>5</b>). The charge
transport type in these materials was characterized by Seebeck coefficient
and Hall-effect measurements. The compounds behave as <i>p</i>- or <i>n</i>-type semiconductors depending on the preparation
method. The samples with the lowest carrier concentration are prepared
from solution and are <i>n</i>-type; <i>p</i>-type
samples can be obtained through solid state reactions exposed in air
in a controllable manner. In the case of Sn compounds, there is a
facile tendency toward oxidation which causes the materials to be
doped with Sn<sup>4+</sup> and thus behave as <i>p</i>-type
semiconductors displaying metal-like conductivity. The compounds appear
to possess very high estimated electron and hole mobilities that exceed
2000 cm<sup>2</sup>/(V s) and 300 cm<sup>2</sup>/(V s), respectively,
as shown in the case of CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub> (<b>1</b>). We also compare the properties of the title hybrid
materials with those of the “all-inorganic” CsSnI<sub>3</sub> and CsPbI<sub>3</sub> prepared using identical synthetic
methods
Structure–Band Gap Relationships in Hexagonal Polytypes and Low-Dimensional Structures of Hybrid Tin Iodide Perovskites
The
present study deals with the structural characterization and classification
of the novel compounds <b>1</b>–<b>8</b> into perovskite
subclasses and proceeds in extracting the structure–band gap
relationships between them. The compounds were obtained from the employment
of small, 3–5-atom-wide organic ammonium ions seeking to discover
new perovskite-like compounds. The compounds reported here adopt unique
or rare structure types akin to the prototype structure perovskite.
When trimethylammonium (TMA) was employed, we obtained TMASnI<sub>3</sub> (<b>1</b>), which is our reference compound for a “perovskitoid”
structure of face-sharing octahedra. The compounds EASnI<sub>3</sub> (<b>2b</b>), GASnI<sub>3</sub> (<b>3a</b>), ACASnI<sub>3</sub> (<b>4</b>), and IMSnI<sub>3</sub> (<b>5</b>)
obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium
(ACA), and imidazolium (IM) cations, respectively, represent the first
entries of the so-called “hexagonal perovskite polytypes”
in the hybrid halide perovskite library. The hexagonal perovskites
define a new family of hybrid halide perovskites with a crystal structure
that emerges from a blend of corner- and face-sharing octahedral connections
in various proportions. The small organic cations can also stabilize
a second structural type characterized by a crystal lattice with reduced
dimensionality. These compounds include the two-dimensional (2D) perovskites
GA<sub>2</sub>SnI<sub>4</sub> (<b>3b</b>) and IPA<sub>3</sub>Sn<sub>2</sub>I<sub>7</sub> (<b>6b</b>) and the one-dimensional
(1D) perovskite IPA<sub>3</sub>SnI<sub>5</sub> (<b>6a</b>).
The known 2D perovskite BA<sub>2</sub>MASn<sub>2</sub>I<sub>7</sub> (<b>7</b>) and the related all-inorganic 1D perovskite “RbSnF<sub>2</sub>I” (<b>8</b>) have also been synthesized. All
compounds have been identified as medium-to-wide-band-gap semiconductors
in the range of <i>E</i><sub>g</sub> = 1.90–2.40
eV, with the band gap progressively decreasing with increased corner-sharing
functionality and increased torsion angle in the octahedral connectivity
Structure–Band Gap Relationships in Hexagonal Polytypes and Low-Dimensional Structures of Hybrid Tin Iodide Perovskites
The
present study deals with the structural characterization and classification
of the novel compounds <b>1</b>–<b>8</b> into perovskite
subclasses and proceeds in extracting the structure–band gap
relationships between them. The compounds were obtained from the employment
of small, 3–5-atom-wide organic ammonium ions seeking to discover
new perovskite-like compounds. The compounds reported here adopt unique
or rare structure types akin to the prototype structure perovskite.
When trimethylammonium (TMA) was employed, we obtained TMASnI<sub>3</sub> (<b>1</b>), which is our reference compound for a “perovskitoid”
structure of face-sharing octahedra. The compounds EASnI<sub>3</sub> (<b>2b</b>), GASnI<sub>3</sub> (<b>3a</b>), ACASnI<sub>3</sub> (<b>4</b>), and IMSnI<sub>3</sub> (<b>5</b>)
obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium
(ACA), and imidazolium (IM) cations, respectively, represent the first
entries of the so-called “hexagonal perovskite polytypes”
in the hybrid halide perovskite library. The hexagonal perovskites
define a new family of hybrid halide perovskites with a crystal structure
that emerges from a blend of corner- and face-sharing octahedral connections
in various proportions. The small organic cations can also stabilize
a second structural type characterized by a crystal lattice with reduced
dimensionality. These compounds include the two-dimensional (2D) perovskites
GA<sub>2</sub>SnI<sub>4</sub> (<b>3b</b>) and IPA<sub>3</sub>Sn<sub>2</sub>I<sub>7</sub> (<b>6b</b>) and the one-dimensional
(1D) perovskite IPA<sub>3</sub>SnI<sub>5</sub> (<b>6a</b>).
The known 2D perovskite BA<sub>2</sub>MASn<sub>2</sub>I<sub>7</sub> (<b>7</b>) and the related all-inorganic 1D perovskite “RbSnF<sub>2</sub>I” (<b>8</b>) have also been synthesized. All
compounds have been identified as medium-to-wide-band-gap semiconductors
in the range of <i>E</i><sub>g</sub> = 1.90–2.40
eV, with the band gap progressively decreasing with increased corner-sharing
functionality and increased torsion angle in the octahedral connectivity
Structure–Band Gap Relationships in Hexagonal Polytypes and Low-Dimensional Structures of Hybrid Tin Iodide Perovskites
The
present study deals with the structural characterization and classification
of the novel compounds <b>1</b>–<b>8</b> into perovskite
subclasses and proceeds in extracting the structure–band gap
relationships between them. The compounds were obtained from the employment
of small, 3–5-atom-wide organic ammonium ions seeking to discover
new perovskite-like compounds. The compounds reported here adopt unique
or rare structure types akin to the prototype structure perovskite.
When trimethylammonium (TMA) was employed, we obtained TMASnI<sub>3</sub> (<b>1</b>), which is our reference compound for a “perovskitoid”
structure of face-sharing octahedra. The compounds EASnI<sub>3</sub> (<b>2b</b>), GASnI<sub>3</sub> (<b>3a</b>), ACASnI<sub>3</sub> (<b>4</b>), and IMSnI<sub>3</sub> (<b>5</b>)
obtained from the use of ethylammonium (EA), guanidinium (GA), acetamidinium
(ACA), and imidazolium (IM) cations, respectively, represent the first
entries of the so-called “hexagonal perovskite polytypes”
in the hybrid halide perovskite library. The hexagonal perovskites
define a new family of hybrid halide perovskites with a crystal structure
that emerges from a blend of corner- and face-sharing octahedral connections
in various proportions. The small organic cations can also stabilize
a second structural type characterized by a crystal lattice with reduced
dimensionality. These compounds include the two-dimensional (2D) perovskites
GA<sub>2</sub>SnI<sub>4</sub> (<b>3b</b>) and IPA<sub>3</sub>Sn<sub>2</sub>I<sub>7</sub> (<b>6b</b>) and the one-dimensional
(1D) perovskite IPA<sub>3</sub>SnI<sub>5</sub> (<b>6a</b>).
The known 2D perovskite BA<sub>2</sub>MASn<sub>2</sub>I<sub>7</sub> (<b>7</b>) and the related all-inorganic 1D perovskite “RbSnF<sub>2</sub>I” (<b>8</b>) have also been synthesized. All
compounds have been identified as medium-to-wide-band-gap semiconductors
in the range of <i>E</i><sub>g</sub> = 1.90–2.40
eV, with the band gap progressively decreasing with increased corner-sharing
functionality and increased torsion angle in the octahedral connectivity
Anomalous Band Gap Behavior in Mixed Sn and Pb Perovskites Enables Broadening of Absorption Spectrum in Solar Cells
Perovskite-based
solar cells have recently been catapulted to the
cutting edge of thin-film photovoltaic research and development because
of their promise for high-power conversion efficiencies and ease of
fabrication. Two types of generic perovskites compounds have been
used in cell fabrication: either Pb- or Sn-based. Here, we describe
the performance of perovskite solar cells based on alloyed perovskite
solid solutions of methylammonium tin iodide and its lead analogue
(CH<sub>3</sub>NH<sub>3</sub>Sn<sub>1–<i>x</i></sub>Pb<sub><i>x</i></sub>I<sub>3</sub>). We exploit the fact
that, the energy band gaps of the mixed Pb/Sn compounds do not follow
a linear trend (the Vegard’s law) in between these two extremes
of 1.55 and 1.35 eV, respectively, but have narrower bandgap (<1.3
eV), thus extending the light absorption into the near-infrared (∼1,050
nm). A series of solution-processed solid-state photovoltaic devices
using a mixture of organic spiro-OMeTAD/lithium bis(trifluoromethylsulfonyl)imide/pyridinium
additives as hole transport layer were fabricated and studied as a
function of Sn to Pb ratio. Our results show that CH<sub>3</sub>NH<sub>3</sub>Sn<sub>0.5</sub>Pb<sub>0.5</sub>I<sub>3</sub> has the broadest
light absorption and highest short-circuit photocurrent density ∼20
mA cm<sup>–2</sup> (obtained under simulated full sunlight
of 100 mW cm<sup>–2</sup>)
Directional Negative Thermal Expansion and Large Poisson Ratio in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Perovskite Revealed by Strong Coherent Shear Phonon Generation
Despite
the enormous amount of attention CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> has received, we are still lacking an in-depth understanding
of its basic properties. In particular, the directional mechanical
and structural characteristics of this material have remained elusive.
Here, we investigate these properties by monitoring the propagation
of longitudinal and shear phonons following the absorption of a femtosecond
pulse along various crystalline directions of a CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> single crystal. We first extract the sound
velocities of longitudinal and transverse phonons along these directions
of the crystal. Our study then reveals the negative directional thermal
expansion of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, which is
responsible for strong coherent shear phonon generation. Finally,
from these observations, we perform elastic characterization of this
material, revealing a large directional Poisson’s ratio, which
reaches 0.7 and that we associate with the weak mechanical stability
of this material. Our results also provide guidelines to fabricate
a transducer of high-frequency transverse phonons
- …