## 3 Results and Discussion
The appearance of XRD diffraction peaks in Figure 3a indicates that the film is composed of a plane structure, indicating that its molecular chains are mainly \(\alpha\)-\(\alpha\) linkages. As a comparison, the XRD result (red line) of PPy prepared under similar conditions using only water as solvent using the chemical oxidation method is also given in Figure 3a. Figure 3b shows the Raman spectrum of the PPy film. The scatting peaks correspond to different vibrations. The diffraction peak at 1575 corresponds to the stretching vibration of the C=C, the diffraction peak at 1047 corresponds to the bending vibration in the C-H symmetry plane, and the Raman peaks at 935 and 986 correspond to the deformation vibration of the pyrrole ring [3; 5]. Calculating the intensity ratio between the stretching vibration peak and the skeleton vibration peak can give a qualitative measurement of the conjugation length. To further investigate the structure of PPy film, the FTIR spectral in the range of 600 to 4000 was recorded as shown in Figure 3c. The broad band at 3000 to 3500 cm\({}^{-1}\) corresponds to N-H and C-H stretching vibrations of PPy. The peaks at 1555 and 1470 cm\({}^{-1}\) can be attributed to the asymmetric and symmetric stretching vibrations of Py rings, respectively. The peak observed at 1314 cm\({}^{-1}\) is due to the C-N stretching in the Py ring of the PPy backbones. The peak at 1194 cm\({}^{-1}\) corresponds to the C-H stretching of the Py ring while the peaks at 1044 and 920 cm\({}^{-1}\) were attributed to C-H in-plane deformation vibration and out-of-plane deformation vibration, respectively. The peak at 790 cm\({}^{-1}\) might be C-H and N-H out of plane deformation vibration [14; 15; 20]. From the XRD results and Raman data, it can be concluded that the prepared PPy film is mainly composed of longer conjugated molecular chains and forms a relatively regular planar configuration, which is conducive to the transfer of carriers within and between the molecular chains. Figure 4a shows the optical transmission spectrum of PPy film in the range of 200-800 nm. It can be seen that the transmittance of the PPy film in the visible light is above 80% and there is no obvious absorption in the ultraviolet region. This can also be seen in the downright inset of Figure 4a. In order to determine the conductivity of the PPy film, I-V and Hall tests were carried out, as shown in Figure 4b. It can be seen from the figure that a larger current can be obtained at a lower voltage, indicating that the PPy film has excellent conductivity. Hall results show that the PPy film shows p-type conductivity. The conductivity and carrier concentration of the prepared PPy film is 1 S/cm and 1 \(\times\) 10\({}^{18}\) cm\({}^{-3}\), respectively. Meanwhile, the carrier mobility is 20 cm/Vs. As mentioned above, the high conductivity can be attributed to the longer conjugated molecular chain and the regular structure of the molecular chains. In order to determine that the conductivity of the PPy film can vary with the preparation conditions, we also prepared samples with different pyrrole monomer and oxide ratios and tested their conductivity. The results are shown in Table 1. In the experiment, we fixed the concentration of pyrrole monomer and changed the concentration of oxidant to prepare a series of samples. It can be seen from the results that sample S2 exhibits the lowest conductivity, and sample S5 exhibits the highest conductivity. The  
conductivity range is 3.8 \(\times\) 10\({}^{-4}\)-2.7 S/cm, which shows that it can be adjusted in a larger range under different preparation conditions.