4 tert butylpyridine

Nickel (II) nitrate hexahydrate (Ni(NO₃)₂ • 6H₂O), trioctylphosphine (TOP, 97%), titanium (IV) tetraisopropoxide (TTIP, >98%), 2-methoxyethanol (CH₃OCH₂CH₂OH, ≥99.5%), lithium perchlorate (LiClO₄, ≥98.0%), ethanol (EtOH, 99.5%) and isopropyl alcohol (IPA, 99.5%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Iodine (I₂, synthetic grade), lithium iodide (LiI, synthetic grade), and poly(ethylene glycol) (PEG, MW~20,000) were supplied by Merck (Rahway, NJ, USA). Acetone ( $\ge$ 99%), 4-tert-butylpyridine (tBP, 96%), and tert-butyl alcohol (tBA, 96%) were acquired from Acros, and 3-methoxypropionitrile (MPN, 99%) was bought from Fluka (Buchs, Switzerland). Transparent titanium dioxide (TiO₂) paste (TL paste, Ti-nanoxide HT/SP, 13 nm), cis-diisothiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium (II) bis(tetrabutylammonium) (N719 dye), and 1,2-dimethyl-3-propylimidazolium iodide (DMPII) were obtained from Solaronix (S.A., Aubonne, Switzerland). Commercial light-scattering TiO₂ particles (ST-41 with 200 nm) were procured from Ishihara Sangyo, Ltd. (Nishi-ku, Osaka, Japan). Nitric acid (HNO₃, 65% solution in water), acetonitrile (ACN, 99.99%) was received from J. T. Baker. Polyester tape (1350F-1, 63 μm) was from the 3M Company (St. Paul, MN, USA).

Unless the special statement, all materials were purchased from Sigma-Aldrich or TCI and used without further purification. The SnO₂ solution was purchased from Alfa Aesar (tin (IV) oxide, 15 wt% in H₂O colloidal dispersion). Dimethylformamide (DMF, 99.8%), dimethyl sulfoxide (DMSO, 99.7%), ethyl acetate (EA, 99.8%) and Chlorobenzene (CB, 99.8%) were purchased from Acros; 4-tert-butyl pyridine (tBP, 96%), lithium bistrifluorosulfonyl imide (LiTFSI, 99.95%), lead iodide (PbI₂, 99.99%) and lead bromine (PbBr₂, 99%) were purchased from TCI. Methylammonium iodide (MAI), methylammonium chloride (MACl), methylammonium bromine (MABr) and 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD, 99.5%) were purchased from Xi'an Polymer Light Technology Corp. Indium tin oxide (ITO, Transmission>95%) substrates were purchased from South China Science & Technology Company limited.