Methylammonium iodide

Lead(II) iodide (PbI₂ purity of 99.99%), bismuth(III)
iodide (BiI₃ 99%),
and cobalt(II) iodide (CoI_2, 95%) were used as Pb²⁺, Co²⁺, and Bi³⁺ sources were purchased from
Sigma Aldrich. 2-Propanol was used as a solvent (99.8%) and was purchased
from Sigma Aldrich. Methylammonium iodide (MAI, 99%) was purchased
from Lumtec and used as an organic part in perovskite. Polyvinyl alcohol
(PVA) was obtained from Merck and was used as a gelling agent. Fluorine-doped
tin oxide (FTO, TCO30-8) glass was obtained from Solaronix and was
used as front contact. Anhydrous N,N-dimethylformamide (DMF) was obtained from J.T Baker and was used
as a PbI₂ solvent. Acetone (99.5%) was used as a stabilizer,
titanium(IV) isopropoxide (98 + %) was used to obtain TiO₂, and ethylene glycol (99.8%) was used as a solvent and purchased
from Gainland Chemical Company, Acros Organics, and VWR Chemicals,
respectively. Citric acid monohydrate (≥99.5%) was used as
a chelate agent, potassium hydroxide (KOH) was used as a conducting
agent, and they were obtained from Tekkim and DETSAN, respectively.

Methylammonium iodide
(MAI, >99.5%), methylammonium
bromide (MABr, >99.5%), and lead(II) iodide (PbI₂, ≥
99.999%) were purchased from Lumtec. Lead(II) bromide (PbBr₂, ≥ 98%) was purchased from TCI. All chemicals were stored
in a nitrogen-filled glovebox and used as received without further
purification.

Methylammonium iodide and bismuth (III) iodide anhydrous were purchased from Lumtec and TCI, respectively. FTO substrates (TEC-15) were purchased from Nippon Sheet Glass (NSG) group. Spiro-MeOTAD was provided by ChemBorum, titanium diisopropoxide bis(acetylacetonate), Li-bis(trifluoromethanesulphonyl) imide (LiTFSI) and 4-tert-butylpyridine (TBP) were purchased from Sigma Aldrich and FK209 Co(III) TFSI from GreatCellSolar. All of the chemicals were used as received without further purification.