## 3 Results and Discussion
### Optimization of the FK209 Cobalt TFSI Concentration in Mesoporous TiO\({}_{2}\)  
The highest efficiency of the PSCs was achieved with the M-TiO\({}_{2}\) layer doped with FK209 cobalt. Optimization of the FK209 concentration was performed to achieve best overall device performance. Table 3 shows that the M-TiO\({}_{2}\) layer doped with 2.5 mg of FK209 has highest conductivity (lower resistivity) and has higher mobility compared to M-TiO\({}_{2}\) prepared with dopant concentration of 1.5-mg or 5-mg. The improved properties obtained with 2.5 mg concentration is due to changes in crystal formation and grain size which affect the surface roughness and wettability of the material. It is clear from Figure 13 that the transparency of the M-TiO\({}_{2}\) doped with FK209 is more than 85% at 400 nm and over the entire visible wavelength range. There is not much variations in transparency with the doping concentration used; 1.5 mg, 2.5 mg or 5 mg. However, there is a slight increase in the transparency between 450-700 nm for the M-TiO\({}_{2}\) doped with 2.5 mg of FK209 compared to other concentration of FK209. Figure 14 shows the absorbance of the M-TiO\({}_{2}\) doped with different concentrations of FK209 measured using Ultraviolet-Visible spectrometry (Cary 6000i). As expected, there is small absorption (10-15%) between 450-800 nm wavelengths range, and much higher absorption between 300-350 nm wavelengths. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Sample** & **Sweep** & **Eff\%** & **FF\%** & **Voc** & **Jsc** & **Vmax** & **Jmax** & **Isc** & **R\({}_{\text{shunt}}\)** & **R\({}_{\text{series}}\)** \\
**Description** & **Direction** & **Eff\%** & **FF\%** & **[mV]** & **[mA/cm\({}^{2}\)]** & **[mV]** & **[mA/cm\({}^{2}\)]** & **[mA]** & **[\(\Omega\).cm\({}^{2}\)]** & **[\(\Omega\).cm\({}^{2}\)]** \\ \hline \multirow{3}{*}{M-TiO\({}_{2}\) Control} & Forward & 10 & 44.8 & 996 & 22.1 & 584 & 16.8 & 7.9 & 1224 & 18 \\  & Backward & 11.6 & 50 & 997 & 22.6 & 668 & 17 & 8.2 & 1289 & 12 \\  & Average & 10.8 & 47.4 & 996.5 & 22.3 & 626 & 16.9 & 8.05 & 1256 & 15 \\ \hline \multirow{3}{*}{M-TiO\({}_{2}\) doped with FK209} & Forward & 15 & 53 & 1049 & 26.4 & 724 & 20.3 & 9.4 & 1305 & 9.7 \\  & Backward & 16.3 & 59.5 & 1052 & 25.4 & 780 & 20.4 & 9.07 & 2024 & 9 \\  & Average & 15.6 & 56.2 & 1050 & 25.9 & 752 & 20.3 & 9.2 & 1664 & 9.3 \\ \hline \multirow{3}{*}{M-TiO\({}_{2}\) doped with FK209/Li\({}^{+}\)} & Forward & 13 & 45.4 & 1011 & 27.1 & 640 & 19.8 & 9.8 & 1249 & 14 \\  & Backward & 15.4 & 53.6 & 1060 & 26.2 & 724 & 20.7 & 9.3 & 3048 & 13.6 \\  & Average & 14.2 & 49.5 & 1035 & 26.9 & 682 & 20.2 & 9.5 & 2148 & 13.8 \\ \hline \multirow{3}{*}{M-TiO\({}_{2}\) doped with Li\({}^{+}\)} & Forward & 11 & 47.1 & 912 & 25.2 & 584 & 18.5 & 9 & 981 & 12.9 \\  & Backward & 13.3 & 51 & 925 & 26.8 & 612 & 20.9 & 9.8 & 1105 & 12.6 \\ \cline{1-1}  & Average & 12.1 & 49 & 918 & 26 & 598 & 19.7 & 9.4 & 1043 & 12.7 \\ \hline \end{tabular}
\end{table} 
Table 2: Perovskite solar cell key parameters measured for the different dopants investigated in this study. It is showing the average value for each set of parameter. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Name**} & **Conductivity** & **Bulk Resistivity** & **Mobility (\(\mu\))** & **Carrier Density** \\  & **(\(\sigma\)) \(\times\) 10\({}^{3}\)** & **(\(\rho\)) \(\times\) 10\({}^{-4}\)** & \(\times\) 10\({}^{3}\) [cm\({}^{2}\)/vs.] & \(\times\) 10\({}^{19}\) [cm\({}^{-3}\)] \\  & **[1/\(\Omega\).cm]** & **[\(\Omega\).cm]** & **[\(\Omega\).cm]** & **[\(\Omega\).cm]** \\ \hline M-TiO\({}_{2}\) doped with FK209 (1.5 mg) & 23 & 0.42 & 3.2 & 4.6 \\ M-TiO\({}_{2}\) doped with FK209 (2.5 mg) & 30 & 0.33 & 8.32 & 2.27 \\ M-TiO\({}_{2}\) doped with FK209 (5 mg) & 27 & 0.37 & 4.8 & 3.52 \\ \hline \end{tabular}
\end{table} 
Table 3: Electrical properties of the M-TiO\({}_{2}\) doped with different concentrations of FK209. The energy gap of the M-TiO\({}_{2}\) film can be extrapolated from the absorption data using Tauc plot [21].