# Excitation of Wet Perovskite Films by Ultrasonic Vibration Improves the Device Performance
## 3 Results and Discussion
Figure 12 shows the SEM images of the MAPbI\({}_{3-x}\)Cl\({}_{x}\) films, where the effect of the perovskite composition and the vibration treatment for 180 s is demonstrated. Again, the SVPT improves the film quality, significantly. The chlorine-rich film subjected to the SVPT for 180 s has a pinhole-free morphology. Comparison of Figures 7 and 12 reveals that both single and mixed halide perovskite films spun at 5000 rpm, followed by the SVPT for 180 s exhibit a defect-free morphology. This approach introduces the SVPT as a low-cost universal approach for the fabrication of defect-free perovskite films on the m-TiO\({}_{2}\) layer, which could also be employed in spray coating, blade coating, and other casting methods. Overall, when considering the foregoing results and discussion, one may conclude that the single and mixed halide perovskite films spun at 5000 rpm for 40 s and followed by the SVPT for 180 s  
Figure 11: XRD peaks of the mixed halide perovskites MAPbI\({}_{3-x}\)Cl\({}_{x}\) fabricated atop the m-TiO\({}_{2}\) layers, at 5000 rpm. The “**” denotes the perovskite peaks and “#” denotes the FTO peaks. Figure 12: SEM images of the mixed halide perovskite (MAPbI\({}_{3-x}\)Cl\({}_{x}\)) films spun at 5000 rpm. (**a**) Pristine sample (PbCl\({}_{2}\) = 30 mg), (**b**) the sample subjected to the SVPT for 180 s (PbCl\({}_{2}\) = 30 mg), (**c**) pristine sample (PbCl\({}_{2}\) = 60 mg), and (**d**) the sample subjected to the SVPT for 180 s (PbCl\({}_{2}\) = 60 mg). exhibit the best performance. As a proof of concept, single and mixed halide perovskite devices were fabricated, without additional treatments on other layers. The devices have the basic structure of glass/TCO/c-TiO\({}_{2}\)/m-TiO\({}_{2}\)/perovskite/HTL/Au. Similar devices fabricated using the one-step method without additional interface engineering typically have shown the PCE of about 6-9% [45]. More recent studies have achieved higher PCE through the optimization of the m-TiO\({}_{2}\) and other layers [40]. The photovoltaic parameters and the JV curves of the champion devices are shown in Table 2 and Figure 13a. The results show that the single halide devices (MAPbI\({}_{3}\)) have a higher performance, as observed by others, as well [46]. The MAPbI\({}_{3}\) device subjected to the SVPT shows a PCE of 12.51%, significantly higher than that of the pristine device (6%). The short circuit current density (\(J_{sc}\)) and fill factor (FF) of the SVPT devices are significantly improved with respect to the control devices, which is attributed to the effective infiltration of the pores of the m-TiO\({}_{2}\) layer by the perovskite solution, as a result of the imposed ultrasonic vibration. Table 2 also shows the estimated shunt and series resistances of the champion devices. A low series resistance and high shunt resistance is desirable for the optimum device performance. The data show that the SVPT significantly increases the shunt resistance. However, the shunt resistances are still low [47]. The low shunt resistance and the low FF are due to manufacturing defects of all the layers. Optimization of other layers, such as the HTL, and employing compositional and interface engineering [48] would further increase the photovoltaic parameters, albeit at the expense of additional steps and costs. Finally, Figure 13b shows the histogram of 50 MAPbI\({}_{3}\) devices treated with the SVPT for 180 s, as well as the histogram of the control devices. It is observed that the PCE of over 50% of the SVPT devices is greater than 11%, which indicates that the SVPT devices are more repeatable and reproducible than the pristine devices.