Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I

Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I

Bibliographic Details
Main Author: HUANG, LING-YI
Language:English
Published: Case Western Reserve University School of Graduate Studies / OhioLINK 2015
Subjects:
Physics
Online Access:http://rave.ohiolink.edu/etdc/view?acc_num=case1436477745
id ndltd-OhioLink-oai-etd.ohiolink.edu-case1436477745
record_format oai_dc
collection NDLTD
language English
sources NDLTD
topic Physics
spellingShingle Physics
HUANG, LING-YI
Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I
author HUANG, LING-YI
author_facet HUANG, LING-YI
author_sort HUANG, LING-YI
title Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I
title_short Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I
title_full Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I
title_fullStr Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I
title_full_unstemmed Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I
title_sort electronic band structure, phonons and exciton binding energies of halide perovskites cssnx<sub>3</sub> with x=cl, br, i
publisher Case Western Reserve University School of Graduate Studies / OhioLINK
publishDate 2015
url http://rave.ohiolink.edu/etdc/view?acc_num=case1436477745
work_keys_str_mv AT huanglingyi electronicbandstructurephononsandexcitonbindingenergiesofhalideperovskitescssnxsub3subwithxclbri
_version_ 1719438467094544384
spelling ndltd-OhioLink-oai-etd.ohiolink.edu-case14364777452021-08-03T06:31:53Z Electronic Band Structure, Phonons and Exciton Binding Energies of Halide Perovskites CsSnX<sub>3</sub> with X=Cl, Br, I HUANG, LING-YI Physics Halide perovskites (ABX<sub>3</sub>) have attracted a large amount of attention since 2009 due to their important applications in solar cells. Though high power conversion efficiencies have been achieved, the underlying reasons for the success are not fully understood. Moreover, some important issues have not yet been resolved, mainly stability issues resulting from phase transitions in halide perovskites. In this thesis, we used the Full-Potential Linear Muffin-Tin Orbital method with Quasiparticle Self-consistent <i>GW</i> (QS<i>GW</i>) to study the electronic band structures and related properties in one family of halide perovskites: CsSnX<sub>3</sub> with X=I, Br, and Cl. We also used density functional perturbation theory to perform phonon calculations for these materials. Our first-principles calculations are compared with experimental data. The main purpose of this study is to understand the fundamental physical properties in these materials and the underlying reasons for the success of these materials in solar cells, and eventually to elucidate information about phase transitions in these materials with the goal of resolving the stability issues.Our QS<i>GW</i> band gaps are in good agreement with experimental gaps. An extremely interesting finding is that the halide perovskites have an “inverted” band structure; i.e. in contrast to most conventional semiconductors, their valence band has a strong Sn-<i>s</i> like character (antibondingly mixed with X-<i>p</i>) while their conduction band has Sn-<i>p</i> character. The unusual characteristic explains (i) the strong luminescence, (ii) the relatively weak band gap dependence on anions, (iii) why the valence band maximum occurs at the <b>R</b>-point, and (iv) the anomalous dependence of the band gap on lattice constants. We also find that the small effective hole mass results in high hole mobility. The free-exciton binding energy was estimated to be of the order of 0.1 meV for CsSnI<sub>3</sub>. Strong LO-TO splittings and large static dielectric constants are found. LO phonons contribute to infrared absorption spectra of α-CsSnBr<sub>3</sub> and α-CsSnCl<sub>3</sub> and Raman spectra of γ-CsSnI<sub>3</sub> and <i>M</i>-CsSnCl<sub>3</sub>. Strong LO-plasmon couplings are expected in these materials because the plasmon frequencies are comparable to the LO phonon frequencies. We find soft phonons, which are phonons with imaginary phonon frequencies, in cubic and tetragonal phases, but not in orthorhombic and monoclinic phases. The phase transitions from the α phase to the β phase and then to the γ phase can be summarized, in terms of space groups and soft phonons, as follows<i>O</i><sub>h</sub><sup>1</sup> ― (<i>M</i><sub>2</sub><sup>+</sup>) ➝ <i>D</i><sub>4h</sub><sup>5</sup> ― (<i>Z</i><sub>5</sub><sup>-</sup>) ➝ <i>D</i><sub>2h</sub><sup>16</sup>, where the <i>M</i><sub>2</sub><sup>+</sup> and <i>Z</i><sub>5</sub><sup>-</sup> are the soft phonons in the cubic and tetragonal phases, respectively. The displacement pattern of the <i>M</i><sub>2</sub><sup>+</sup> mode is shown in Fig. 5.4 while the displacement pattern of the <i>Z</i><sub>5</sub><sup>-</sup> mode is shown in Fig. 5.5. The notation <i>M</i><sub>2</sub><sup>+</sup> means that the phonon at k-point <b>M</b> of the cubic Brillouin zone belonging to the irreducible representation 2+ of the point group of that k-point, <i>D</i><sub>4h</sub>, leads to the transformation of the crystal to a new one with the <i>D</i><sub>4h</sub><sup>5</sup> subgroup as spacegroup and similar for the second step. 2015-09-03 English text Case Western Reserve University School of Graduate Studies / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=case1436477745 http://rave.ohiolink.edu/etdc/view?acc_num=case1436477745 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

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