## 3 Results and Discussion
Figure 1: (**a**) Schematic diagram of work function of each functional layer material; (**b**) structure diagram of ITO/NiO\({}_{\text{x}}\)/HDA-BiI\({}_{\text{S}}\)//PCBM/Ag inverted device. performance parameter of this sample device after polarization at different voltages are shown in Figure 4. Where (0) represents the unpolarized state, (1), (2), (3), and (4) represent the conditions of polarization at 0.6 V, 0.8 V, 1.0 V, and 1.2 V for 30 s, respectively, while the solid dot plots represent the forward scan and the hollow ones represent the reverse sweep. From this figure, it can be found that under different voltage polarization conditions, the forward scan V\({}_{\text{oc}}\) and fill factor of the device are lower than those of the reverse sweep, while the J\({}_{\text{sc}}\) is higher than that of the reverse sweep. Both the PCE of forward scan and reverse scan show an increasing trend with the increase of polarization voltage, which achieves the expected effect. The highest PCE of 0.112% was obtained for the forward scan of the device when the constant polarization voltage was 1.2 V. This result is an improvement of about 41 times with respect to the 0.6 V polarized device and about five times with respect to the unpolarized device. Figure 2: Different magnifications SEM top view of organic–inorganic hybrid ferroelectric thin films formed by different chlorobenzene dropping time. (**a,b**) 0 s in the second stage, (**c,d**) 5 s in the second stage, (**e,f**) 10 s in the second stage, and (**g,h**) 15 s in the second stage. Figure 3: SEM top view of organic–inorganic hybrid ferroelectric thin films formed by different chlorobenzene drops. (**a**,**b**) 100 \(\mu\)L, (**c**,**d**)80 \(\mu\)L, (**e**,**f**) 60 \(\mu\)L, and (**g**,**h**) 40 \(\mu\)L.  
To further investigate the effect of the ferroelectric films prepared by the anti-solvent process on the device performance, the devices with ITO/NiO\({}_{\text{x}}\)/HDA-Bi\({}_{5}\) (anti-solvent process)/PCBM/Ag structure were also polarized and the device performance after polarization at different voltages was tested. The J-V curves tested after polarization at 0.6 V, 0.8 V, 1.0 V, and 1.2 V, as shown in Figure S5a-d. Figure 5 shows the trend of each performance parameter of the optimized device with the polarization voltage, indicating that the J\({}_{\text{Sc}}\), both forward and reverse sweep, has a significant increase. The V\({}_{\text{oc}}\) does not change much, or even decreases slightly, but the PCE still has a substantial increase, which is mainly attributed to the very large improvement in the photogenerated current obtained after polarization. The trend of the overall increase in fill factor also shows that the photovoltaic performance of the device has been really improved. In our experiments, the highest PCE was achieved at a polarization voltage of 1.2 V for both forward and reverse scan tests, with a forward scan of 0.084%, an improvement of 58.4% compared to the unpolarized device, and a reverse scan of 0.089%, an improvement of about 147.5%. By comparing with the device without the anti-solvent process, it can be found that the optimized device has a more stable performance change during the polarization process, the overall device performance is higher, and the J-V curves of forward and reverse scan are closer. In particular, after the lower voltage polarization, the performance is substantially improved compared to the unoptimized device. An increase in the short circuit current density can be related to polarization switching. However, in a DC poling field experiment, there is no way to distinguish between increased current density due to electrical leakage currents (conductivity) and polarization switching. The polarization switching has been  
Figure 4: The performance parameters of unoptimized devices vary with the polarization conditions.