Duijnstee, E.A. orcid.org/0000-0002-7002-1523, Gallant, B.M. orcid.org/0000-0001-7413-291X, Holzhey, P. orcid.org/0000-0003-3688-1607 et al. (25 more authors) (2023) Understanding the degradation of methylenediammonium and its role in phase-stabilizing formamidinium lead triiodide. Journal of the American Chemical Society, 145 (18). pp. 10275-10284. ISSN 0002-7863
Abstract
Formamidinium lead triiodide (FAPbI3) is the leading candidate for single-junction metal-halide perovskite photovoltaics, despite the metastability of this phase. To enhance its ambient-phase stability and produce world-record photovoltaic efficiencies, methylenediammonium dichloride (MDACl2) has been used as an additive in FAPbI3. MDA2+ has been reported as incorporated into the perovskite lattice alongside Cl-. However, the precise function and role of MDA2+ remain uncertain. Here, we grow FAPbI3 single crystals from a solution containing MDACl2 (FAPbI3-M). We demonstrate that FAPbI3-M crystals are stable against transformation to the photoinactive δ-phase for more than one year under ambient conditions. Critically, we reveal that MDA2+ is not the direct cause of the enhanced material stability. Instead, MDA2+ degrades rapidly to produce ammonium and methaniminium, which subsequently oligomerizes to yield hexamethylenetetramine (HMTA). FAPbI3 crystals grown from a solution containing HMTA (FAPbI3-H) replicate the enhanced α-phase stability of FAPbI3-M. However, we further determine that HMTA is unstable in the perovskite precursor solution, where reaction with FA+ is possible, leading instead to the formation of tetrahydrotriazinium (THTZ-H+). By a combination of liquid- and solid-state NMR techniques, we show that THTZ-H+ is selectively incorporated into the bulk of both FAPbI3-M and FAPbI3-H at ∼0.5 mol % and infer that this addition is responsible for the improved α-phase stability.
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Copyright, Publisher and Additional Information: | © 2023 The Authors. Published by American Chemical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. | ||||||
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Institution: | The University of Sheffield | ||||||
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Department of Physics and Astronomy (Sheffield) | ||||||
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Depositing User: | Symplectic Sheffield | ||||||
Date Deposited: | 18 May 2023 11:02 | ||||||
Last Modified: | 18 May 2023 11:02 | ||||||
Published Version: | http://dx.doi.org/10.1021/jacs.3c01531 | ||||||
Status: | Published | ||||||
Publisher: | American Chemical Society (ACS) | ||||||
Refereed: | Yes | ||||||
Identification Number: | https://doi.org/10.1021/jacs.3c01531 | ||||||
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