First-principles calculations of phonons and Raman spectra in monoclinic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="normal">CsSnCl</mml:mi><mml:msub><mml:mrow /><mml:mn>3</mml:mn></mml:msub></mml:math>

Huang, Ling-yi; Lambrecht, Walter R. L.

doi:10.1103/physrevb.91.075206

Cited by 13 publications

(7 citation statements)

References 30 publications

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“…Recently, forbidden LO scattering also was proposed to explain the presence of unexpected strong Raman peaks in the spectra of the halide perovskites CsSnX 3 (X = I, Br, Cl). [45,46] Several other explanations are much less probable. Our samples are grown by sulfurization of BaZrO 3 in CS 2 , so at first sight one might expect O impurities to be a possible source of the anomalous scattering.…”

Section: Discussionmentioning

confidence: 99%

Stability and Band-Gap Tuning of the Chalcogenide Perovskite BaZrS3 in Raman and Optical Investigations at High Pressures

et al. 2017

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We report experiments and calculations investigating the pressure and temperature dependences of the optical phonons in BaZrS 3 , and the pressure dependence of its absorption edge. BaZrS 3 is a chalcogenide perovskite in a novel class of materials being considered for photovoltaics. It is studied by Raman spectroscopy as functions of temperature (at 1 atm) and pressure (at 120K and 295K), and by pressure-transmission spectroscopy at 295K. Density functional theory (DFT) calculations predict the allowed Raman lines, their intensities, their pressure-shifts, and the band gap pressure-shift. Cooling shifts all but one of the phonon peaks to higher frequencies; the temperature coefficients are typical of semiconductors. A strong low-temperature peak at 392.3 cm-1 is attributed to resonant forbidden LO scattering; its shift with temperature has the opposite sign. The pressure coefficients of the phonon frequencies for all observed Raman peaks are positive, indicating no mode softening. The rates of pressure shift also are typical, and show the customary scaling with phonon frequency. Experiment and theory show good agreement on the pressureinduced frequency shifts. The BaZrS 3 absorption edge moves to lower energy with pressure, reflecting reduction of the band gap. The measured shift is ~ −0.015 eV/GPa, slightly less than the DFT result of −0.025 eV/GPa. We find no evidence that the perovskite structure of BaZrS 3 undergoes any phase changes under hydrostatic pressure to at least 8.9 GPa. Our results indicate the robust structural stability of BaZrS 3 , and suggest cation alloying as a viable approach for band gap engineering for photovoltaic and other applications.

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Section: Discussionmentioning

confidence: 99%

Stability and Band-Gap Tuning of the Chalcogenide Perovskite BaZrS3 in Raman and Optical Investigations at High Pressures

et al. 2017

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“…31 In general, accurate theoretical description of perovskites requires the use of large unit cells to capture the disorder related to organic cations. 32,33 Most theoretical contributions use density functional theory (DFT) simulations, 34 with focus on the electronic and optical properties of bulk HOPV 35,36 and single-crystal perovskites. 37 The large number of atoms in the unit cell of organic 2D perovskites makes prohibitive the simulations including many-body effects such as the Bethe-Salpeter equation (BSE) to account for the excitonic effects.…”

Section: Introductionmentioning

confidence: 99%

Excitonic States in Semiconducting Two-Dimensional Perovskites

Molina-Sánchez

2018

ACS Appl. Energy Mater.

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Hybrid organic/inorganic perovskites have emerged as efficient semiconductor materials for applications in photo-voltaic solar cells with conversion efficiency above 20 %. Recent experiments have synthesized ultra-thin two-dimensional (2D) organic perovskites with optical properties similar to those of 2D materials like monolayer MoS 2 : large exciton binding energy and excitonic effects at room temperature. In addition, 2D perovskites are synthesized with a simple fabrication process with potential low-cost and large-scale manufacture.Up to now, state-of-the-art simulations of the excitonic states have been limited to the study of bulk organic perovskites. The large number of atoms in the unit cell and the complex role of the organic molecules makes inefficient the use of ab initio methods. In this work, we define a simplified crystal structure to calculate the optical properties of 2D perovskites, replacing the molecular cations with inorganic atoms. We can thus apply state-of-the-art, parameter-free and predictive ab initio methods like the GW method and the Bethe-Salpeter equation to obtain the excitonic states of a model 2D perovskite. We find that optical properties of 2D perovskites are strongly influenced by excitonic effects, with binding energies up to 600 meV. Moreover, the 1 arXiv:1812.04332v1 [cond-mat.mtrl-sci] 11 Dec 2018 optical absorption is carried out at the bromine and lead atoms and therefore the results are useful for a qualitatively understanding of the optical properties of organic 2D perovskites. Cs 2 PbBr 4 MonolayerCsPbBr 3 Bulkz Cs-Cs < l a t e x i t s h a 1 _ b a s e 6 4 = " E L B U x g Q K 2 7 x V a 8 2 8 O E C E H 8 d 7 w 0 Y = " > A A A B + 3 i c b V B N S 8 N A E N 3 4 W e t X r E c v w S J 4 s S Q i 6 L H Y i 8 c K 9 g P a E D b b T b t 0 d x N 2 J 9 I a 8 l e 8 e F D E q 3 / E m / / G b Z u D t j 4 Y e L w 3 w 8 y 8 M O F M g + t + W 2 v r G 5 t b 2 6 W d 8 u 7 e / s G h f V R p 6 z h V h L Z I z G P M k m B S r J Y F K X c g d i Z B e E M m K I E + N Q Q T B Q z t z p k h B U m Y O I q m x C 8 5 Z d X S f u y 5 r k 1 7 / 6 q W r 8 t 4 i i h E 3 S K z p G H r l E d 3 a E m a i G C J u g Z v a I 3 K 7 d e r H f r Y 9 G 6 Z h U z x + g P r M 8 f j g i U w Q = = < / l a t e x i t > < l a t e x i t s h a 1 _ b a s e 6 4 = " E L B U x g Q K 2 7 x V a 8 2 8 O E C E H 8 d 7 w 0 Y = " > A A A B + 3 i c b V B N S 8 N A E N 3 4 W e t X r E c v w S J 4 s S Q i 6 L H Y i 8 c K 9 g P a E D b b T b t 0 d x N 2 J 9 I a 8 l e 8 e F D E q 3 / E m / / G b Z u D t j 4 Y e L w 3 w 8 y 8 M O F M g + t + W 2 v r G 5 t b 2 6 W d 8 u 7 e / s G h f V R p 6 z h V h L Z I z G P M k m B S r J Y F K X c g d i Z B e E M m K I E + N Q Q T B Q z t z p k h B U m Y O I q m x C 8 5 Z d X S f u y 5 r k 1 7 / 6 q W r 8 t 4 i i h E 3 S K z p G H r l E d 3 a E m a i G C J u g Z v a I 3 K 7 d e r H f r Y 9 G 6 Z h U z x + g P r M 8 f j g i U w Q = = < / l a t e x i t > < l a t e x i t s h a 1 _ b a s e 6 4 = " E L B U x g Q K 2 7 x V a 8 2 8 O E C E H 8 d 7 w 0 Y = " > A A A B + 3 i c b V B N S 8 N A E N 3 4 W e t X r...

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“…The model presented here in principle also applies to the stannates and plumbates although the lone‐pair related distortion in these cases is less pronounced and the s 2 electrons behave more as an inert‐pair . Nonetheless, for CsSnCl 3 , a model in terms of SnCl 3 dipole carrying units applies and the higher ionicity/stronger electrostatic interactions compared to CsSnI 3 leads to a lowest energy monoclinic phase . Even in CsSnI 3 the lowest energy phase may be the Pnma phase which corresponds to an intermediate orientation of the SnI 3 units between FE and AFE.…”

Section: Resultsmentioning

confidence: 95%

“…Similar rotated octahedron phases also occur for the plumbates but are further complicated in the hybrid organic ones by the symmetry breaking of the organic ion. However, the relation between the perovskite and the non‐perovskite phases such as the yellow phase in CsSnI 3 or the monoclinic phase of CsSnCl 3 are not yet understood. These phases are usually described in terms of edge‐sharing rather than corner‐sharing octahedra.…”

Section: Introductionmentioning

confidence: 99%

“…

effects such as humidity or light exposure but intrinsically due to the existence of other competing phases which do not share these favorable features in the band structures. However, the relation between the perovskite and the nonperovskite phases such as the yellow phase [8] in CsSnI 3 or the monoclinic phase [9] of CsSnCl 3 are not yet understood. It is thus important to understand the relative stability and relations between these crystallographic phases, how they influence the band structures, and how their trends depend on the chemical substitution space.

Some of the relations within the perovskite type of structures are already well understood.

…”

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Understanding the Crystallographic Phase Relations in Alkali‐Trihalogeno‐Germanates in Terms of Ferroelectric or Antiferroelectric Arrangements of the Tetrahedral GeX₃ Units

Radha

Lambrecht

2019

Adv Elect Materials

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effects such as humidity or light exposure but intrinsically due to the existence of other competing phases which do not share these favorable features in the band structures. In fact, these other phases may well be an intermediate step in the decomposition process of the material to the AX and (Ge,Sn,Pb)X 2 reaction products. It is thus important to understand the relative stability and relations between these crystallographic phases, how they influence the band structures, and how their trends depend on the chemical substitution space.Some of the relations within the perovskite type of structures are already well understood. Specifically, we have recently shown that both the Sn and Pb based compounds in this family primarily undergo octahedral rotations related to the Goldschmidt tolerance factor t < 1 while the Ge and Si based ones show a ferroelectric off-centering of the central IV-atom leading to a rhombohedrally distorted perovskite. [5] The rotational distortions in CsSnX 3 were studied both experimentally [6] and computationally [7] and are well known from oxide perovskites. Similar rotated octahedron phases also occur for the plumbates but are further complicated in the hybrid organic ones by the symmetry breaking of the organic ion. However, the relation between the perovskite and the nonperovskite phases such as the yellow phase [8] in CsSnI 3 or the monoclinic phase [9] of CsSnCl 3 are not yet understood. These phases are usually described in terms of edge-sharing rather than corner-sharing octahedra.Because in the stannates the yellow phase has a higher density and the rotations also are clearly driven by the need to make the space for the alkali ion tighter, we proposed in previous work that to avoid the non-perovskite phases one needs to make the size of the IV-X network smaller relative to the A filler cation. First this already explains why larger organic ions are preferred to Cs in the plumbates but also guides the way to how to develop lead-free alternatives. This naturally led us to explore the Ge and Si based materials. [10][11][12] In fact, the CsGeX 3 family is found not to exhibit octahedron rotational distortions but a ferroelectric rhombohedral phase (R) [13] at low temperature and a cubic perovskite phase at high temperature and was shown to have a band structure maintaining the favorable features of the perovskite structure. However the situation is different forThe alkali-trihalogeno-germanates AGeX 3 with A: Rb or Cs and X a halogen (I, Br, Cl) along with the corresponding stannates (ASnX 3 ) and plumbates (APbX 3 ) exhibit a large variety of crystal structures, some of which are of the perovskite type. These materials, better known as "halide perovskites" have recently gained worldwide attention as promising photovoltaic and more broadly opto-electronic materials. However, their stability problems relative to the non-perovskite phases are a major issue. It is shown that some of the phase relations in these materials can be understood in terms of the relative orientation of the GeX ...

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First-principles calculations of phonons and Raman spectra in monoclinicCsSnCl3

Cited by 13 publications

References 30 publications

Stability and Band-Gap Tuning of the Chalcogenide Perovskite BaZrS3 in Raman and Optical Investigations at High Pressures

Stability and Band-Gap Tuning of the Chalcogenide Perovskite BaZrS3 in Raman and Optical Investigations at High Pressures

Excitonic States in Semiconducting Two-Dimensional Perovskites

Understanding the Crystallographic Phase Relations in Alkali‐Trihalogeno‐Germanates in Terms of Ferroelectric or Antiferroelectric Arrangements of the Tetrahedral GeX₃ Units

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First-principles calculations of phonons and Raman spectra in monoclinicCsSnCl3

Cited by 13 publications

References 30 publications

Stability and Band-Gap Tuning of the Chalcogenide Perovskite BaZrS3 in Raman and Optical Investigations at High Pressures

Stability and Band-Gap Tuning of the Chalcogenide Perovskite BaZrS3 in Raman and Optical Investigations at High Pressures

Excitonic States in Semiconducting Two-Dimensional Perovskites

Understanding the Crystallographic Phase Relations in Alkali‐Trihalogeno‐Germanates in Terms of Ferroelectric or Antiferroelectric Arrangements of the Tetrahedral GeX3 Units

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Product

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Understanding the Crystallographic Phase Relations in Alkali‐Trihalogeno‐Germanates in Terms of Ferroelectric or Antiferroelectric Arrangements of the Tetrahedral GeX₃ Units