Fabrication of Perovskite Solar Cells with ITO and SWCNT Substrates

ITO-patterned glass substrates (10 Ω sq⁻¹, Huananxiangcheng Ltd.) and ITO-patterned PEN flexible substrates (<15 Ω sq⁻¹, Peccell) were cleaned with deionized water, acetone, and isopropyl alcohol respectively. Then ITO-patterned glass substrates were treated with an oxygen plasma process (Emitech K1050X, 230 V, 100 W) for 5 min before fabrication. The rest fabrication processes of ITO-based and SWCNT-based perovskite solar cells were the same. Cu:NiO_x NPs solution was spin-coated on ITO-based and SWCNT-based substrates at 2000 rpm for 20 s, followed by a post-heating process at 120 °C for 10 min. Then, these Cu:NiO_x-coated substrates were moved to a UV-ozone cleaning device to receive 5 min of UV-Ozone treatment. Then the KI layer was prepared on top of the Cu:NiOx via spin-coating, the spin-coating condition of the KI layer is 2000 rpm, 30 s with a solution concentration of 2 mg/ml (in water), and heated at 100 °C for 10 min. Here, the composition of the perovskite layer is Cs_0.05FA_0.80MA_0.15Pb(I_xBr_1-x)₃, the perovskite precursor solution was prepared by dissolving 470.23 mg PbI₂, 66.06 mg PbBr₂, 15.59 mg CsI, 166.64 mg formamidinium iodide, and 19.15 mg methylammonium bromide in a 1 ml solution of 4:1 V/V DMF/DMSO. Following this, the solution was stirred overnight at room temperature. Then the perovskite layer was formed by spin-coating according to a two-step protocol, 1000 rpm for 10 s and 4000 rpm for 35 s, 80 µl CB was dropped 5 s before the end of the second step. Then the film was heated at 100 °C for 60 min on a hotplate. A passivation layer, choline chloride was then fabricated on top of the perovskite layer at 4000 rpm, 30 s with a solution concentration of 1 mg/mL (in IPA), and heated at 100 °C for 30 min. The SnO₂ layer was prepared with the SnO₂ butanol solution, which was diluted with 1-butanol until the concentration reached 1.25 wt%. Subsequently, SnO₂ thin film was spin-coated on top of the perovskite with the diluted solution at 6000 rpm (2000 rpm/s) for 30 s and heated at 100 °C for 40 min. PCBM was employed as the electron transport material, PC₆₁BM (20 mg/ml in CB) was spin-coated at 2000 rpm for 20 s, and dried at 100 °C for 5 min. As for the back SWCNT electrode, the transfer process is the same as the front SWCNT transfer process. For control cells, BCP solution (0.5 mg/mL in IPA) was spin-coated on top of PC₆₁BM. Finally, a 100 nm thick Ag electrode was deposited in a thermal evaporator (>3 × 10⁻⁶Torr, Moorefield thermal evaporator) to complete the fabrication process.