## 3 Results and Discussion
### CNT/Si Devices with Films of Similar Transmittance  
Due to the difference between the transmittance values, another experiment was performed with CNT films with similar transmittance of about 95%. Whilst thinner films were used, the slow-filtered films were again inhomogeneous on the macroscale and the obviously thicker regions were avoided when sections were cut for use in the solar cells. An attempt was made to produce slow and fast-filtered films of roughly equivalent transmittance. Figure 7 shows that both sets of devices have the same maximum PCE of around 5.4%. In this case, however, the slow-filtered films produced a higher average PCE, with a higher average J\({}_{\text{sc}}\), and V\({}_{\text{oc}}\), but a lower average FF. As per the films used previously, the slow-filtered film segments used for solar device application were still thinner than the fast-filtered films. There was some variance between the films and so two films were used in each case. The fast-filtered films were found to be between 85% and 95% and the slower filtered films were from 95% to 97%. It is expected that this difference in thickness for the fast-filtered films accounts for the variance in device performance with these films. It is known that, when the transmittance of the CNT films approaches 90% and above that the devices will decline in performance as the ability of super thin films to transfer current is poor as the CNT network becomes patchy as thickness decreases. This explains the high variability in PCE for devices with fast-filtered films (Table 4) but it is surprising to see that the devices with slow-filtered films performed well and \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{4}{c}{**Slow-filtered Films**} & \multicolumn{4}{c}{**Fast-Filtered Films**} \\ \cline{2-7}  & \multirow{2}{*}{\(\mathbf{T_{550}}\)} & **Sheet** & \(\mathbf{\sigma_{dc}}\):\(\mathbf{\sigma_{OP}}\) **Ratio** & \multirow{2}{*}{\(\mathbf{T_{550}}\)} & **Sheet** & \(\mathbf{\sigma_{dc}}\):\(\mathbf{\sigma_{OP}}\) **Ratio** \\  & & **Resistance (\(\Omega\))** & **Slow-Filtered** & & **Resistance (\(\Omega\))** & **Fast-Filtered** \\ \hline As Prepared & 0.79 & 440 & 0.379425 & 0.53 & 220 & 0.621004 \\ \hline HCl 1 & 0.79 & 427 & 0.390997 & 0.53 & 200 & 0.682166 \\ \hline Thionyl Chloride & \multirow{2}{*}{0.79} & \multirow{2}{*}{319} & \multirow{2}{*}{0.524073} & \multirow{2}{*}{0.53} & \multirow{2}{*}{142} & \multirow{2}{*}{0.962568} \\ \cline{1-1} \cline{5-5}  & & & & & & \\ \hline HCl 2 & 0.79 & 325 & 0.513056 & 0.53 & 143 & 0.95487 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(\sigma_{\text{dc}}\): \(\sigma_{\text{OP}}\) ratio calculations for slow and fast films used in solar device production. Note that HCl was used in lieu of HF as HF would have dissolved the glass on which the CNT films were attached. with low variation considering that they all had transmittances above 90%. This performance again highlights the importance of the film smoothness. The sheet resistance values for these films were all an order of magnitude higher than that used previously. In addition, the values were much more varied and values on the order of \(\times 10^{6}\)\(\Omega\) were occasionally reported. These issues are all likely due to how thin the films were, thinner films will conduct poorly compared to thick films and will have more charge gaps and holes throughout the network. The outlying data points were removed when average sheet resistance was calculated. The sheet resistance and transmittance measurements were combined to produce \(\sigma_{\text{dc}}\):\(\sigma_{\text{OP}}\) ratios for the slow and fast-filtered films to allow for a better comparison. Table 5 shows a different result to Table 3, with the slow-filtered films producing higher \(\sigma_{\text{dc}}\):\(\sigma_{\text{OP}}\) ratios than the fast-filtered films.