biostudies-literatureDuijnstee EADeutsche ForschungsgemeinschaftMinisterio de Ciencia e Innovaci??nEusko JaurlaritzaRank PrizeKing Abdullah University of Science and TechnologyIkerbasque, Basque Foundation for ScienceEuropean CommissionResearch Councils UKUniversity of WarwickPolymat Foundation10275-10284https://www.ebi.ac.uk/biostudies/studies/S-EPMC10176466biostudies-literatureUnknown145(18)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 Journal of the American Chemical SocietyUnderstanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.PMC10176466EP/R029431EP/R029946/1PID2021-129084OB-I00EP/T025077/1CH 1672/3-1EP/V027131/1RED2018-102815-TEP/T015063/1PIBA_2022_1_0031764787EC_2022_1_0011EP/V010840/1EP/L01551X/1EP/S004947/1EP/T028513/1EP/P033229/1RTI2018-101782-B-I00OSR-2018-CARF/CCF-3079861985OSR-2019-CRG8-4095Nicholas RJKober-Czerny MRamadan AJJohnston MBNugraha MISnaith HJMatzen AHung EYAnthopoulos TDDelgado JLSansom HCCollavini SSturdza BKWright ADXia CKubicki DJZhou SGallant BMHolzhey PSmith JSeo SFilip MRSaha SGedda MLin YHDuijnstee EAGutmann MJLim JfalseUnderstanding the Degradation of Methylenediammonium and Its Role in Phase-Stabilizing Formamidinium Lead Triiodide.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 2023-01-01T00:00:00Z2023 May2025-04-05T16:13:58.53Z2025-04-05T16:13:58.53ZS-EPMC101764663711573310.1021/jacs.3c01531