## 3 Results
characteristic hump at \(20\approx 20^{\circ}\) and noisy behavior in the XRD diffractogram is observed, which imply \(\pi\)-\(\pi\) stacking of the aromatic rings in PFB polymer and exhibits the amorphous nature of PFB. The bond dynamics of PFB are investigated by FTIR spectroscopy within a wide energy range of 600-4200 cm\({}^{-1}\), as shown in Figure 3d. In the FTIR spectroscopy, one measures the absorption/transmission of photons by molecules in the infrared (IR) region. Furthermore, different peaks represent the areas of IR spectrum where specific bond vibrations occur. The FTIR spectrum acts as a fingerprint for the identification of different compounds, molecules, functional groups, and nature of their bonds. From left to right, two strong peaks are observed at 651 and 812 cm\({}^{-1}\), both of which correspond to C-H bending vibration. A medium-strong peak at 1269 cm\({}^{-1}\) reveals C-N stretching, whereas an intense peak at 1500 cm\({}^{-1}\) demonstrates C-C stretching mode. The medium-weak peak at 1600 cm\({}^{-1}\) and strong spike at 2357 cm\({}^{-1}\) are attributed to C=C stretching of conjugated alkene and C\(\equiv\)C stretching modes, respectively. There are also some relatively broad and weak peaks at 2846-2918 cm\({}^{-1}\) containing C-H stretch mode. The sample displays a relatively broad intense hydrogen-bonded O-H stretch absorption centered on 3700 cm\({}^{-1}\). The overall FTIR analysis of PFB is presented in Table 1.  
To study the microelectronic properties of the Ag/PFB/p-Si heterojunction, _I-V_ characteristics are carried out at 300 K in dark conditions. The _I-V_ graph shown in Figure 4a is nonlinear and asymmetric, which demonstrate that p-Si/PFB heterojunction exhibits rectifying current behavior in the forward bias. An exponential increase in the forward current is observed due to the formation of a depletion region between the p-Si and PFB thin film. Rectification ratio (_RR_), the ratio of forward and reverse current, is extracted from the _I-V_ curve of the heterojunction whose maximum value is found to be 23.6 at \(\pm\)7.2 V, and the value of turn-on voltage \(V_{\text{turn on}}\) is 3.92 V. In the case of heavily doped semiconductors, rectifying behavior of the heterojunction is well described by thermionic emission-diffusion theory and/or field emission theory [26]. Assuming that PFB has as much high hole mobility as a heavily doped p-type semiconductor [27], then the forward-bias characteristics of  
Figure 3: (**a**) UV–vis absorption spectrum, (**b**) [PERSON]’s plot for bandgap measurement, (**c**) XRD diffractogram, and (**d**) FTIR spectrum of PFB thin film. the Ag/PFB/p-Si can be studied by thermionic emission-diffusion theory according to Equation (1). The current can be calculated by the following equation:  
\[I=I_{0}\left[\exp\left\{\frac{q(V-IR_{s}\,)}{nkT}\right\}-1\right] \tag{1}\]  
where \(I\) is forward current, \(I_{0}\) represents reverse saturation current, \(n\) is the ideality factor, \(q\) is electronic charge, \(V\) is applied voltage, \(R_{\rm{s}}\) is series resistance, \(T\) is absolute temperature, and \(k\) is the Boltzmann constant. \(I_{0}\) in Equation (1) can be expressed as:  
\[I_{0}=AA^{*}T^{2}\mbox{exp}\left[\frac{-q\Phi_{b}}{kT}\right] \tag{2}\] \begin{table}
\begin{tabular}{l l} \hline
**Band (cm\({}^{-1}\))** & **Assignment** \\ \hline
2918 & C-H stretch, alkyl \\
2846 & C-H stretch, aldehyde \\
2357 & Stretch alkyne (may be coordinated type) \\
1600 & C=C stretching of conjugated alkene \\
1500 & C-C stretch aldehyde \\
1313 & C-N stretch \\
1269 & C-N stretch \\
812 & C-H bending vibration \\
651 & C-H bend alkene \\ \hline \end{tabular}
\end{table} 
Table 1: PFB molecular composition with chemical bond dynamics. Figure 4: (**a**) \(I\)–\(V\) curves at room temperature, (**b**) ln (I)–V characteristics, (**c**) junction resistance vs. V curve, and (**d**) F(V) vs. V plot for the Ag/PFB/p-Si device.