# Ammonia Gas Sensing Characteristic of P3 HT-rGO-MWCNT Composite Films
## 3 Results and Discussion
### Ammonia Gas Sensing of P3 HT-Based Composite Films
The improved sensitivity of the sensor based on the Py-rGO blend was attributed to the oxygen and structural defects after chemical reduction, which makes the rGO material act as a p-type semiconductor. [PERSON] et al. [45] also showed that the adsorption efficiency of gas molecules (including NH\({}_{3}\)) was improved through the use of MWCNTs resulting from the enlarging effective surface area. In addition, MWCNTs embedded in rGO can be thought of as \"nano-bridges\" for the transfer of charge carriers. In this work, these \"nano-bridges\" were clearly shown in the FE-SEM microscope image (Figure 2c). Furthermore, inorganic nanoparticles embedded in the polymer would fill up most of the cracked spots in the polymer that were usually created during the post-annealing process [27]. Consequently, in the nanocomposite films, the cracked spots that acted as the charged traps were eliminated. From the above analysis results, the improvement in the performance of the sensors made from PGC composite film was attributed to the heterojunction of P3 HT/rGO, P3 HT/CNT, and a reduction in the charged traps in the polymer film. To clarify the role of rGO in the sensor, the sensors are based on P3 HT-MWCNTs (without rGO), where the weight ratio of P3 HT:MWCNT is 60:40 (abbreviated to P3C) were also fabricated. The sensitivity and relative sensitivity of the two types of devices were shown in Figure 6. The results showed that the response of the sensor linearly decreases with a decrease in ammonia gas concentration (\(C\), ppm), and the slope of the linear plot reflects the relative sensitivity (\(RS\)) of the sensor. Thus, \(RS\) can be determined by the following formula:  
\[RS=\frac{\Delta\eta}{\Delta C}(\%/\text{ppm}) \tag{3}\] \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Sensing Material** & **NH\({}_{3}\) Concentration (ppm)** & **Sensor Sensitivity (\%)** & **Reference** \\ \hline rGO+P3 HT & 50 & 12.63 & [41] \\ \hline SWCNT & 500 & 1.9 & [42] \\ \hline rGO+TiO\({}_{2}\) & 30 & 3.5 & [43] \\ \hline polythiophene/ MWCNTs & 2000 & 15 & [23] \\ \hline PGC-60 & 10 & 5 & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 1: PGC-60 ammonia sensor sensitivity in a comparison with literature data. Figure 6: The (**a**) sensitivity and (**b**) relative sensitivity of P3 HT-rGO-MWCNTs comparing to those of P3 HT-MWCNTs sensors. The result also indicated that the relative sensitivity of the P3C and PGC composite sensors was 0.012%/ppm and 0.031%/ppm, respectively. This clearly demonstrates that rGO played an important role in improving the performance parameters of sensors based on organic composites. Here, the relative sensitivity of the PGC sensor is about 2.5 times greater than that of the P3C sensor and about 1.5 times greater than that of the PEDOT:PSS sensor [46]. In summary, we would like to point out that in three-component composite sensors (namely P3 HT, rGO, and MWCNTs), each component plays its specific and important role. While rGO is an excellent electron transporter, as pointed out in [47], a conducting polymer, P3 HT, seen as a p-type organic semiconductor, is the adsorption activator to NH\({}_{3}\) gas. Owing to P3 HT, electrons of NH\({}_{3}\) molecules are temporarily detached from their molecule. Then due to rGO, electrons move fast inside films and couple with holes in P3 HT. Serving as charge carrier \"nano-bridges\", MWCNTs favor holes transported from P3 HT to the cathode of the device. In general, all three components in PGC sensors have significantly contributed to the improvement of both the sensitivity and response time in NH\({}_{3}\) gas sensing. The enhancement in charge transport during the performance of a composite-based NH\({}_{3}\) sensor can be explained by using the scheme of the energy levels, as shown in Figure 7.