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Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs₂TiX₆)

Kavanagh, Seán R; Savory, Christopher N; Liga, Shanti M; Konstantatos, Gerasimos; Walsh, Aron; Scanlon, David O; (2022) Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs₂TiX₆). The Journal of Physical Chemistry Letters , 13 pp. 10965-10975. 10.1021/acs.jpclett.2c02436. (In press). Green open access

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Abstract

Low-cost, nontoxic, and earth-abundant photovoltaic materials are long-sought targets in the solar cell research community. Perovskite-inspired materials have emerged as promising candidates for this goal, with researchers employing materials design strategies including structural, dimensional, and compositional transformations to avoid the use of rare and toxic elemental constituents, while attempting to maintain high optoelectronic performance. These strategies have recently been invoked to propose Ti-based vacancy-ordered halide perovskites (A2TiX6; A = CH3NH3, Cs, Rb, or K; X = I, Br, or Cl) for photovoltaic operation, following the initial promise of Cs2SnX6 compounds. Theoretical investigations of these materials, however, consistently overestimate their band gaps, a fundamental property for photovoltaic applications. Here, we reveal strong excitonic effects as the origin of this discrepancy between theory and experiment, a consequence of both low structural dimensionality and band localization. These findings have vital implications for the optoelectronic application of these compounds while also highlighting the importance of frontier-orbital character for chemical substitution in materials design strategies.

Type: Article
Title: Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs₂TiX₆)
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acs.jpclett.2c02436
Publisher version: https://doi.org/10.1021/acs.jpclett.2c02436
Language: English
Additional information: This is an Open Access article published under a Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/).
Keywords: Density functional theory, Electrical conductivity, Excitons, Materials, Perovskites
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10160377
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