# Excitation of Wet Perovskite Films by Ultrasonic Vibration Improves the Device Performance
## 2 Materials and Methods  
Methylammonium iodide (MAI, 99.5%) was supplied by Xi'an Reagents Co., Xi'an, China. Dimethyl sulfoxide (DMSO, 99.5%), hydrogen chloride (HCl, 37.5%), lead iodide (98.5%), ethanol (99.9%), chlorobenzene (CB, 99.9%), gamma-butylrolactone (GBL, 99%) \(N\),_N_-dimethyl formamide (DMF,  
Figure 1: Perovskite thin film deposition procedure, using the ultrasonic substrate vibration post treatment (SVPT) and annealing. 99.8%), toluene (98.8%), titanium (IV) isopropoxide (97%), bis(tri-fluoromethane)sulfonamide lithium salt (99.95%), acetonitrile (99.8%), 4-tert-butylpyridine (96%), spiro-OMeTAD, titanium dioxide paste, and lead chloride (98.5%) were purchased from Sigma-Aldrich (Saint Louis, MI, USA). FTO-coated glass substrates (10 \(\times\) 10 mm) were sequentially washed by detergent, deionized water, and 2-propanol in an ultrasonic bath for 30 min, followed by UV-ozone treatment, for 15 min, in order to increase the surface energy, and therefore the wettability. For the preparation of the c-TiO\({}_{2}\) layer, 2.54 mL of titanium isopropoxide was diluted in 16.9 mL of ethanol, and 350 \(\mu\)L of HCl (2 M) was diluted in 16.9 mL of ethanol. Then, the acidic solution was added to the titanium isopropoxide solution dropwise, under vigorous stirring conditions [27]. The resulting solution was spun onto the FTO-coated glass at 2000 rpm, for 60 s, and the film was annealed at 500 \({}^{\circ}\)C, for 30 min. To fabricate the mesoporous layer, titanium dioxide paste was diluted in ethanol (2:7 mass ratio), stirred overnight, and spun on the c-TiO\({}_{2}\) layer at 5000 rpm, for 30 s, and annealed at 500 \({}^{\circ}\)C, for 30 min. The single halide perovskite (MAPbl\({}_{3}\)) precursor solution was prepared by dissolving 600 mg of PbI\({}_{2}\) and 200 mg of MAI powders in 300 \(\upmu\)l of DMSO and 700 \(\upmu\)L of GBL. To prepare the mixed halide perovskite (MAPbl\({}_{3-x}\)Cl\({}_{x}\)) precursor with a small amount of Cl, 30 or 60 mg of PbCl\({}_{2}\) was added to the aforementioned single halide precursor solution. The perovskite solution was spun atop the m-TiO\({}_{2}\) layer first at 1000 rpm, for 15 s, and then at 4000 or 5000 rpm, for 30 s. In each experiment (with or without the SVPT), after 30 s from the first stage of the spinning, 60 \(\upmu\)l of toluene was dripped onto the perovskite film (suitable for the area of 10 \(\times\) 10 mm), and the prepared wet film was annealed at 100 \({}^{\circ}\)C, for 10 min. The reported compositions of the precursors were chosen based on the literature reports and several trials to achieve fully-covered and impurity-free perovskite thin films. For the samples subjected to the SVPT, the wet spun perovskite films were placed and secured on a steel box, inside which an ultrasonic piezoelectric transducer was installed to provide vertical vibration to the samples (Yuhuan Clangsonic Ultrasonic Co., Ltd, Zhejiang, China). The transducer was powered by a signal generator operated at 5 W and 40 kHz, for various durations, up to 240 s. At these conditions, the amplitude of the vibrations is about 10 nm [24]. The wet samples were immediately subjected to the SVPT and then annealed at 100 \({}^{\circ}\)C, for 10 min. The pristine wet spun samples (no SVPT) were immediately annealed. Thus, we have tentatively neglected the effect of a possible natural convection on the pristine sample due to a short (\(\sim\)3 min) time elapse. This is justified because a considerable effect has not been observed if the spun samples are kept under still nitrogen atmosphere for several minutes [28]. In fact, only gas blowing with high pressure can increase the evaporation rate and consequently the film nanostructure [29]. Thus, it is justified to state that the control and the SVPT samples were subjected to identical fabrication and annealing steps, expect for the SVPT process.