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

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

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


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.

Original languageEnglish
Pages (from-to)10965-10975
Number of pages11
JournalJournal of Physical Chemistry Letters
Issue number47
StatePublished - 1 Dec 2022

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© 2022 The Authors. Published by American Chemical Society.


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