Impact of the Organic Cation on the Optoelectronic Properties of Formamidinium Lead Triiodide
Abstract
Metal halide perovskites have proven to be excellent light-harvesting materials in photovoltaic devices whose efficiencies are rapidly improving. Here, we examine the temperature-dependent photon absorption, exciton binding energy, and band gap of FAPbI 3 (thin film) and find remarkably different behavior across the β–γ phase transition compared with MAPbI 3 . While MAPbI 3 has shown abrupt changes in the band gap and exciton binding energy, values for FAPbI 3 vary smoothly over a range of 100–160 K in accordance with a more gradual transition. In addition, we find that the charge-carrier mobility in FAPbI 3 exhibits a clear T –0.5 trend with temperature, in excellent agreement with theoretical predictions that assume electron–phonon interactions to be governed by the Fröhlich mechanism but in contrast to the T –1.5 dependence previously observed for MAPbI 3 . Finally, we directly observe intraexcitonic transitions in FAPbI 3 at low temperature, from which we determine a low exciton binding energy of only 5.3 meV at 10 K.
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The fitting was performed simultaneously on the dielectric function and conductivity spectra to ensure internal consistency of the extracted parameters.
“The fitting was performed simultaneously on the dielectric function and conductivity spectra to ensure internal consistency of the extracted parameters [15,38,41].”
From Impact of Sub-picosecond Timing Errors on Complex Conductivity Extraction in Terahertz Time-Domain Spectroscopy of Ultrathin FAPbI3 Films (2026) · cites this paper as [41]
The Graphical TOC Entry relates photoconductivity to the change in dielectric function, but does not say the two spectra were fitted simultaneously. Its described fits concern absorption spectra or temperature-dependent mobility, not a joint fit to ensure parameter consistency (searched for simultaneous fitting, dielectric-function fitting, and internal consistency). (LLM, conf=0.73)
Experimental — accuracy not yet measuredThe uncorrected dataset yields unphysical values of epsilon_DC and epsilon_infinity (approximately -13), whereas the corrected data produce values around 33, which are consistent with literature reports.
“As summarized in Table 1, the uncorrected dataset yields unphysical values of ε DC and ε ∞ (approximately 13), whereas the corrected data produce values around 33, which are consistent with literature reports [38,39,41].”
From Impact of Sub-picosecond Timing Errors on Complex Conductivity Extraction in Terahertz Time-Domain Spectroscopy of Ultrathin FAPbI3 Films (2026) · cites this paper as [41]
The Graphical TOC Entry discusses the dielectric environment of FAPbI₃ and its effect on exciton binding, but does not report εDC or ε∞ values. Searches for corrected and uncorrected dielectric data, including values near 13 and 33, found no passage addressing the claimed comparison or its consistency with literature reports. (LLM, conf=0.76)
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References 71 · Cited by 68
Research works printed but not linked: 4
- [1](1) Yang, W. S.; Noh, J. H.; Jeon, N. J.; Kim, Y. C.; Ryu, S.; Seo, J.; Seok, S. I. Highperformance Photovoltaic Perovskite Layers Fabricated Through Intramolecular Exchange. Science 2015 , 348 , 1234-1237. -
- [27](27) La-O-Vorakiat, C.; Xia, H.; Kadro, J.; Salim, T.; Zhao, D.; Ahmed, T.; Lam, Y. M.; Zhu, J.-X.; Marcus, R. A.; Michel-Beyerle, M.-E. et al. Phonon Mode Transforma- tion Across the OrthohombicTetragonal Phase Transition in a Lead Iodide Perovskite CH 3 NH 3 PbI 3 : ATerahertz Time-Domain Spectroscopy Approach. J. Phys. Chem. Lett. 2016 , 7 , 1-6. -
- [44](44) Klingshirn, C. F. Semiconductor Optics , 1st ed.; Springer: page 166, 1997. -
- [58](58) Baikie, T.; Fang, Y.; Kadro, J. M.; Schreyer, M.; Wei, F.; Mhaisalkar, S. G.; Gr¨ atzel, M.; White, T. J. Synthesis and Crystal Chemistry of the Hybrid Perovskite (CH 3 NH 3 PbI 3 ) for Solid-State Sensitized Solar Applications. J. Chem. Mater. A 2013 , 1 , 5628. -
- Authors
- Davies, C. L., Borchert, J., Xia, C. Q., Milot, R. L., Kraus, H., Johnston, M. B., & Herz, L. M.
- Affiliations
- University of Oxford (GB)
- University of Warwick (GB)
- Corresponding author
- Johnston, Michael B.
- Herz, Laura M.
- Venue
- The Journal of Physical Chemistry Letters
- Publisher
- American Chemical Society (ACS)
- Published
- 2018-07-23
- Volume
- 9
- Issue
- 16
- Pages
- 4502-4511
- ISSN
- 1948-7185 (ISSN-L)
- OpenAlex
- W2883657028
- Cited by
- 68
- References
- 71
- Citations by year
- 2026: 3 · 2025: 5 · 2024: 4 · 2023: 7 · 2022: 9 · 2021: 18 · 2020: 11 · 2019: 6 · 2018: 5
- FWCI
- 3.83
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- The Journal of Physical Chemistry Letters (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Engineering and Physical Sciences Research Council (EP/P033229/1, EP/L024667/1, EP/P006329/1, EP/L01551X/1)
- Topics
- Physical Sciences › Engineering › Electrical and Electronic Engineering › Perovskite Materials and Applications
- Physical Sciences › Materials Science › Materials Chemistry › 2D Materials and Applications
- Physical Sciences › Materials Science › Materials Chemistry › Ferroelectric and Piezoelectric Materials
- Keywords
- FAPbI3, halide perovskites, exciton binding energy, band gap, temperature dependence of absorption, carrier mobility, Fröhlich electron-phonon interaction, optoelectronic properties
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