Fk209

Titanium diisopropoxide
bis(acetylacetonate) (TAA), 4-tert-butylpyridine
(t-BP), tin(IV) chloride pentahydrate (SnCl₄), bis(trifluoromethane) sulfonamide lithium salt (LiTFSI), FK209
[tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)-cobalt(III)-tris(bis(trifluoromethylsulfonyl)imide)],
chlorobenzene, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF)
were supplied from Sigma-Aldrich. Mesoporous TiO₂ (30-NRT),
FAI, MAI, and MACl were purchased from GreatCell Solar. HAT6 and PbI₂ were purchased from TCI. Spiro-OMeTAD was purchased from
Merck. All of the purchased chemicals were used as received without
further purification.

Indium tin oxide substrates
(ITO), methylammonium iodide (MAI, 98%), and 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene
(Spiro-MeOTAD, 99%) were purchased from Ossila. Isopropyl alcohol
(IPA, 99.7%), anhydrous dimethylformamide (DMF, 99.8%), dimethyl sulfoxide
(DMSO, 99.8%), acetonitrile (99.8%), chlorobenzene (99.9%), 4-tert-butylpyridine (4-tBP, 96%), lithium
bis(trifluoromethanesulfonyl)imide (LiTFSI, 99.95%), tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)-tris(bis(trifluoromethylsulfonyl)imide)
(FK209, 98%), and pHEMA were purchased from Sigma-Aldrich. Tin (IV)
oxide (SnO₂), Hellmanex III detergent, and lead iodide
(PbI₂) were purchased from Alfa Aesar.

For the synthesis of the Rb_0.05Cs_0.1FA_0.85PbI₃ perovskite, the following materials were used: lead (II) iodide (Sigma-Aldrich, 99%, St. Louis, MO, USA), formamidinium iodide (FAI) (Sigma-Aldrich, ≥99%, St. Louis, MO, USA), cesium iodide (Sigma-Aldrich, ≥99%, St. Louis, MO, USA), rubidium iodide (Sigma-Aldrich, ≥99%, St. Louis, MO, USA), N,N-dimethylformamide (DMF) (Merck, p.a., Darmstadt, Germany), dimethyl sulfoxide (DMSO) (Merck, p.a., Darmstadt, Germany), chlorobenzene (Merck, p.a., Darmstadt, Germany).
15 × 15 mm indium tin oxide (ITO) coated glass plates (Lumtech, ρ ~15 Ω/sq, CA, USA) were used as substrate and transparent front electrode. For the synthesis of the TiO₂ ETL titanium diisopropoxide (Sigma-Aldrich, 99%, St. Louis, MO, USA), acetylacetonate (Sigma-Aldrich, 99%, St. Louis, MO, USA) and ethanol (Merck, p.a., Darmstadt, Germany) were used. For the preparation of the spiro-OMeTAD HTL, spiro-OMeTAD (Merck, ≥99%, Darmstadt, Germany), 4-tert-butylpyridine (tBP) (Sigma-Aldrich, 99%, St. Louis, MO, USA), FK209 (Sigma-Aldrich, 99%, St. Louis, MO, USA), bis-(trifluoromethane)sulfonimide lithium salt (LiTFSI) (Sigma-Aldrich, 99%, St. Louis, MO, USA) and acetonitrile (Merck, p.a., Darmstadt, Germany) were used.