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

Kavanagh, Seán R.; Savory, Chris; Liga, Shanti M.; Konstantatos, Gerasimos; Walsh, Aron; Scanlon, David O.

doi:10.1021/acs.jpclett.2c02436

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

Seán R. Kavanagh

, Chris Savory

, Shanti M. Liga, Gerasimos Konstantatos

, Aron Walsh

, David O. Scanlon

The Journal of Physical Chemistry Letters, Volume: 13, Issue: 47, Pages: 10965 - 10975

Swansea University Author: Chris Savory

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DOI (Published version): 10.1021/acs.jpclett.2c02436

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...

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Published in:	The Journal of Physical Chemistry Letters
ISSN:	1948-7185 1948-7185
Published:	American Chemical Society (ACS) 2022
Online Access:	Check full text
URI:	https://cronfa.swan.ac.uk/Record/cronfa70861

first_indexed	2025-11-06T22:01:34Z
last_indexed	2026-01-09T05:31:30Z
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spelling	2026-01-08T14:52:03.8677240 v2 70861 2025-11-06 Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6) 1951890f7d79de7d173a378c5dc17bca 0000-0002-9052-7484 Chris Savory Chris Savory true false 2025-11-06 EAAS 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. Journal Article The Journal of Physical Chemistry Letters 13 47 10965 10975 American Chemical Society (ACS) 1948-7185 1948-7185 1 12 2022 2022-12-01 10.1021/acs.jpclett.2c02436 COLLEGE NANME Engineering and Applied Sciences School COLLEGE CODE EAAS Swansea University Another institution paid the OA fee S.R.K. acknowledges the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials (CDT-ACM) (EP/S023259/1) for funding a Ph.D. studentship. C.N.S. is grateful to the Department of Chemistry at UCL and the Ramsay Memorial Fellowship Trust for the funding of a Ramsay fellowship. D.O.S. acknowledges support from the EPSRC (EP/N01572X/1) and from the European Research Council, ERC (Grant 758345). The authors acknowledge the use of the UCL Kathleen High Performance Computing Facility (Kathleen@UCL), the Imperial College Research Computing Service, and associated support services in the completion of this work. Via membership of the UK’s HEC Materials Chemistry Consortium, which is funded by the EPSRC (EP/L000202, EP/R029431, and EP/T022213), this work used the ARCHER2 UK National Supercomputing Service (www.archer2.ac.uk) and the UK Materials and Molecular Modelling (MMM) Hub (Thomas EP/P020194 and Young EP/T022213). The authors acknowledge financial support from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation program (Grant Agreement 725165) as well as from the European Unions Horizon 2020 research and innovation program under Marie Skodowska-Curie Grant Agreement 713729. This project has received funding also from the Spanish State Research Agency, through the Severo Ochoa Center of Excellence (CEX2019-000910-S), the CERCA Programme/Generalitat de Catalunya and Fundacio Mir-Puig. The authors also acknowledge funding by the Fundacio Joan Ribas Araquistain (FJRA). This project was funded also by EQC2019-005797-P (AEI/FEDER UE). 2026-01-08T14:52:03.8677240 2025-11-06T16:51:12.2067059 Faculty of Science and Engineering School of Engineering and Applied Sciences - Chemistry Seán R. Kavanagh 0000-0003-4577-9647 1 Chris Savory 0000-0002-9052-7484 2 Shanti M. Liga 3 Gerasimos Konstantatos 0000-0001-7701-8127 4 Aron Walsh 0000-0001-5460-7033 5 David O. Scanlon 0000-0001-9174-8601 6 70861__35928__bac76d8f4bf340d1ae1e51b6e452592d.pdf 70861.VoR.pdf 2026-01-08T14:49:32.5455665 Output 6701582 application/pdf Version of Record true © 2022 The Authors. Released under the terms of a Creative Commons Attribution (CC-BY) 4.0 license. true eng https://creativecommons.org/licenses/by/4.0/
title	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)
spellingShingle	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6) Chris Savory
title_short	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)
title_full	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)
title_fullStr	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)
title_full_unstemmed	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)
title_sort	Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)
author_id_str_mv	1951890f7d79de7d173a378c5dc17bca
author_id_fullname_str_mv	1951890f7d79de7d173a378c5dc17bca_***_Chris Savory
author	Chris Savory
author2	Seán R. Kavanagh Chris Savory Shanti M. Liga Gerasimos Konstantatos Aron Walsh David O. Scanlon
format	Journal article
container_title	The Journal of Physical Chemistry Letters
container_volume	13
container_issue	47
container_start_page	10965
publishDate	2022
institution	Swansea University
issn	1948-7185 1948-7185
doi_str_mv	10.1021/acs.jpclett.2c02436
publisher	American Chemical Society (ACS)
college_str	Faculty of Science and Engineering
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department_str	School of Engineering and Applied Sciences - Chemistry{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Chemistry
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description	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.
published_date	2022-12-01T05:33:48Z
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Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6)

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