4.2.5. Fabrication of PCBM-PSCs with nanopatterned TiO2 layer
The fluorine-doped tin oxide (FTO) glass was cleaned using water, ethanol, and acetone. Then, the compact TiO2 layer was created by spin-coating a precursor solution made of 1 ml of titanium diisopropoxide bis(acetylacetonate) (75 wt% in isopropanol, Sigma Aldrich, St. Louis, MO, USA) in 6 ml of butanol (99%, Daejung Chemicals, Siheung-si, Korea) onto the FTO at 4000 rpm for 20 s, followed by annealing at 250°C for 10 min. This process was repeated twice. To form the mp-TiO2 layer, 1 g of TiO2 paste (Ti-Nanoxide T/SP, Solaronix, Aubonne, Switzerland) was diluted in 12 ml of anhydrous ethanol (99.9%, Daejung Chemicals, Siheung-si, Korea), and spin-coated on a compact TiO2/FTO. After slightly evaporating the solvent by prebaking on a hotplate at 70°C for 1 min, the PFPE mold was placed on the mp-TiO2/compact TiO2/FTO substrate and heat-pressed for 5 min at 70°C with a pressure of 2 bar. After removing the mold, the resulting nanopatterned mp-TiO2/compact TiO2/FTO substrate was then annealed at 500 °C for 1 hour. The PCBM-perovskite layer was created by spin coating the PCBM-perovskite precursor solution at 700 rpm onto the nanopatterned mp-TiO2 layer through the hot-casting technique at 90 °C, followed by annealing at 130 °C for 1 hour. The HTM layer was spin coated at 4000 rpm for 60 s and dried overnight in a glovebox. All the procedure were conducted inside a dried air-filled glovebox. Finally, the Au electrode was deposited through thermal evaporation.