*2.2. Fabrication of Device*

FTO glasses were ultrasonically cleaned with detergent, acetone, ethanol, and isopropyl alcohol sequentially. After that, they were dried under hot air and treated in ultraviolet-ozone for 15 min. The clean FTO substrate was then soaked in dilute 0.2 M aqueous TiCl4 solution at 70 ◦C for 1 h, and washed with deionized water, then annealed at 200 ◦C for 60 min. In the Glove box, dropping the perovskite (CH3NH3I: 159 mg, PbI2: 461 mg, DMF: 600 mg, and DMSO: 78 mg) onto the substrate and deposited it by spincoating at 4000 rpm for 30 s. Solvent treatment was conducted at late 15 s, where 150 μL chlorobenzene was dropped on the spinning substrate followed by annealing at 100 ◦C for 10 min. After cooling to room temperature, the hole transport materials prepared before (3 mg/mL in dimethylcarbinol) were spin-coated onto the perovskite layer at 2000 rpm for 30 s and followed by 10 min of thermal annealing at 90 ◦C. Besides, Spiro-OMeTAD hole transport material was used in the comparative experiment: 20 μL spiro-OMeTAD solution, containing 36.1 mg spiro-OMeTAD, 14.4 μL t-BP and 9 μL Li-TFSI solution (520 mg in acetonitrile), was spin-coated on the perovskite layer at 4000 rpm for 30 s. Lastly, a carbon black counter electrode was coated on the top of the device by blade coating and sintered at 80 ◦C for 30 min.
