Anhydrous chloroform

ITO substrate was cleaned and treated with UV-ozone with same procedure for fabrication of solar cell devices. The 1.9 wt% colloidal ZnO solution was prepared by diluting the stock ZnO nanoparticle solution (Aldrich, 2.5 wt% in isopropanol and propylene glycol) with anhydrous isopropanol (Sigma-Aldrich, 99.5%). The ZnO solution was spin-coated on the ITO substrate at 5000 rpm for 30 s, which was followed by drying at 100 °C for 10 min. The ZnO coated ITO substrate was further treated with UV-ozone for 10 min before spin-coating of perovskite solution. The DMF amount for the perovskite solution was adjusted to 660 mg. The perovskite solution was spin-coated at 4000 rpm for 25 s, to which 0.2 mL of anhydrous chloroform (Sigma-Aldrich, >99.0%) was dropped after 10 s of spinning. The resulting film was annealed at 80 °C for 1 min followed by 150 °C for 1 min. On top of the perovskite layer, 0.5 wt.% of Poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (Poly-TPD, Lumtec) solution in chlorobenzene was spin-coated at 4000 rpm for 30 s. The device was completed with thermal evaporation of 10 nm-thick molybdenum trioxide and 100 nm-thick silver layers. The size of active layer was 0.100 cm².

Anhydrous N,N-dimethylformamide (DMF), anhydrous toluene, anhydrous chloroform, sodium thiosulfate (Na₂S₂O₃), N-bromosuccinimide (NBS), and tetrakis(triphenylphosphine)palladium(0) (Pd(PPh₃)₄) were purchased from Sigma-Aldrich. Anhydrous acetonitrile was purchased from Alfa Aesar. All the Soxhlet solvents, anhydrous bromine, anhydrous sodium sulfate (Na₂SO₄) were purchased from Daejung Chemicals & Metals Co. LTD. (Korea). (3,3′-Difluoro-[2,2′-bithiophene]-5,5′-diyl)bis(trimethylstannane), 2,6-bis(trimethylstannyl)dithieno[3,2-b:2′,3′-d]thiophene, and (E)-1,2-bis(5-(trimethylstannyl)thiophen-2-yl)ethene were purchased from SunaTech Inc. (China). 2,5-Bis(2-decyltetradecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP2DT), 3,6-bis(5-bromothiophen-2-yl)-2,5-bis(2-decyltetradecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (Br-DPP2DT-Br) and 5,5′-bis(trimethylstannyl)-2,2′-bithiophene were prepared by following the method reported in literature.^{26 (link)} Tetrabutylammonium hexafluorophosphate (TBAPF₆) was purchased for electrochemistry from TCI. CDCl₃ NMR solvent was purchased from Cambridge Isotope Laboratories. Toluene and DMF, used for polymerization, were separately degassed by freeze–pump–thaw three cycling and added to the reaction mixture. The other solvents were used without further purification.