Inverted solar cell fabrication (p-i-n)

ITO glasses were washed twice with ethanol in an ultrasonic bath for 15 min. NiO_x (20 mg ml⁻¹ in H₂O) was spin-coated on dry and ultraviolet (UV)–treated ITO at 2000 rpm for 40 s and then heated at 100°C for 10 min. The thickness of the NiO_x film was approximately 20 nm. The coated ITO was then moved to a glove box. The perovskite solution was spin-coated on the NiO_x HTL according to a procedure where the spin-coating speed and duration were increased from 1000 rpm for 10 s to 6000 rpm for 30 s. A total of 110 μl of the PPP polymer with various concentrations (0, 0.04, 0.1, 0.6, and 1.0 mg ml⁻¹) of the CB antisolvent was deposited for 15 s before the end of the procedure, and then the perovskite solution was annealed at 100°C for 20 min to obtain the bright perovskite film with a thickness of 750 nm. After that, 20 mg of PCBM (99% purity) and 5 mg of fullerene (C60, 99.5% purity) were dissolved in 1 ml of CB and spin-coated on the perovskite film at 3000 rpm for 30 s, and then the ETL films were annealed on a 60°C heating stage for 10 min. The thickness of the ETL is approximately 45 nm. After cooling to room temperature, the BCP solution (0.5 mg ml⁻¹ in isopropanol) was spin-coated at 5800 rpm for 30 s. Last, the fabrication of the devices was accomplished by thermally evaporating chromium (Cr; 5 nm) and gold (Au; 100 nm) electrodes under a vacuum of 2 × 10⁻⁶ mbar (0.1 cm² effective area).