Understanding the degradation of methylenediammonium and its role in phase-stabilizing formamidinium lead triiodide

Duijnstee, EA; Gallant, BM; Holzhey, P; Kubicki, DJ; Collavini, S; Sturdza, BK; Nicholas, RJ; Sansom, HC; Smith, J; Gutmann, MJ; Saha, S; Gedda, M; Nugraha, MI; Kober-Czerny, M; Xia, C; Wright, AD; Lin, Y-H; Ramadan, AJ; Matzen, A; Hung, EY-H; Seo, S; Zhou, S; Lim, J; Anthopoulos, TD; Filip, MR; Johnston, MB; Delgado, JL; Snaith, HJ

Journal article

Understanding the degradation of methylenediammonium and its role in phase-stabilizing formamidinium lead triiodide

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.

Publication status:: Published

Peer review status:: Peer reviewed

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APA Style

Duijnstee, E. A., Gallant, B. M., Holzhey, P., Kubicki, D. J., Collavini, S., Sturdza, B. K., Nicholas, R. J., Sansom, H. C., Smith, J., Gutmann, M. J., Saha, S., Gedda, M., Nugraha, M. I., Kober-Czerny, M., Xia, C., Wright, A. D., Lin, Y.-H., Ramadan, A. J., Matzen, A., … Snaith, H. J. (2023). Understanding the degradation of methylenediammonium and its role in phase-stabilizing formamidinium lead triiodide. Journal of the American Chemical Society, 145(18), 10275–10284.

MLA Style

Duijnstee, E. A., et al. “Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.” Journal of the American Chemical Society, vol. 145, no. 18, American Chemical Society, 2023, pp. 10275–84.

Chicago Style

Duijnstee, EA, BM Gallant, P Holzhey, DJ Kubicki, S Collavini, BK Sturdza, RJ Nicholas, et al. 2023. “Understanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.” Journal of the American Chemical Society 145 (18): 10275–84.
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