Titanium diisopropoxide bis acetylacetonate solution

The perovskite films in this work were deposited on top of cover glasses or ITO glass. The substrate glasses were cleaned extensively by deionized water, acetone, and isopropanol. For the HTL deposition, the PTAA (Sigma-Aldrich) was dissolved in toluene with a concentration of 5 mg mL⁻¹ and spin-coated on the substrates at 5000 rpm for 30 s. The spun PTAA films were annealed at 100 °C for 10 min. For the ETL deposition, a compact titanium dioxide (TiO₂) layer of about 40 nm was deposited by spray pyrolysis of 7 mL 2-propanol solution containing 0.6 mL titanium diisopropoxide bis(acetylacetonate) solution (75% in 2-propanol, Sigma-Aldrich) and 0.4 mL acetylacetone at 450 °C in air. The FA_0.95Cs_0.05PbI₃ precursor solution was prepared by dissolving 0.4 M Pb²⁺ in dimethyl sulfoxide (DMSO) and dimethylformamide (v/v = 3/7) mixed solvent. Perovskite films were deposited using a three-step spin-coating procedure with the first step of 100 rpm for 3 s, the second step of 3500 rpm for 10 s, and the last step of 5000 rpm for 30 s. Toluene (1 mL) was applied on the spinning substrates at 20 s of the third step. After spin coating, the substrates were annealed at 170 °C for 27 min. The encapsulated perovskite films were capped with PMMA (Mw about 120,000) film by spin-coating 15 mg ml⁻¹ PMMA in chlorobenzene solution at 4000 rpm for 35 s.

Solar cells were prepared under high-humidity ambient atmosphere. First, FTO-coated glass substrates were cleaned by ultrasonication in detergent, deionized water, acetone and isopropanol for 15 min, respectively. Then, the substrates were dried with a N₂ gun and subjected to an ultraviolet/ozone cleaning system for 15 min. Subsequently, the titanium diisopropoxide bis(acetylacetonate) solution (75% in 2-propanol, Sigma-Aldrich) diluted in isopropanol (0.15 M) was spin-coated onto the FTO substrates at 4000 r.p.m. for 30 s and annealed at 150 °C for 10 min.
A commercial TiO₂ paste (Dyesol 18NRT, Greatcell) diluted in ethanol (1:2.5, weight ratio) was dropped onto the compact TiO₂ and spun at 3000 r.p.m. for 30 s. After drying at 100 °C, the TiO₂ thin films were annealed at 500 °C for 30 min and then slowly cooled to room temperature. The mesoporous TiO₂ was treated with a TiCl₄ aqueous solution (40 mM) at 70 °C for 30 min. After that, the substrate was washed with ethanol and deionized water. The CH₃NH₃PbI₃ film was fabricated using the sequential deposition method. Finally, a counter electrode was prepared by doctor blading the commercial carbon paste onto the perovskite film and annealed at 100 °C for 30 min.