## 3 Results and Discussion
### Optimization by Changing the Carrier Concentration  
During the modeling, first light impinges on one side of the cell while the other is completely dark and then it does so the other way around, and bifaciality (\(B_{f}\)) is computed. The I-V curve is calculated varying the carriers' concentration in each layer, and the electrical properties are recorded. Figures 11-13 in the Appendix A show the open circuit voltage (\(V_{oc}\)), short circuit current density (\(J_{sc}\)), fill factor (\(FF\)), and energy conversion efficiency (\(E_{ff}\)) as a function of \(c-Si(n)\) donor concentration (Figure 11), \(a-Si:H(p^{+})\) acceptor concentration (Figure 12), and \(a-Si:H(n^{+})\) donor concentration (Figure 13) for the Standard and Atacama Desert spectra. Figure 13 shows the optimization of the crystalline silicon layer \(c-Si(n)\) when donor concentration ranges are between \(0.4\times 10^{17}\) 1/cm\({}^{3}\) and \(1.4\times 10^{17}\) 1/cm\({}^{3}\). When the light impinges on the back side, the current density reaches the highest value, \(J_{sc}=34.88\) mA/cm\({}^{2}\), for a donor concentration of \(9.5\times 10^{16}\) 1/cm\({}^{3}\) (red circle in Figure 11). When the light hits from the front, the \(J_{SC}\) increases its value as the concentration of donors increases, and, in the modeling, it is not possible to infinit \begin{table}
\begin{tabular}{c c c} \hline
**Contact Parameters** & **Front Contact** & **Back Contact** \\ \hline Width (nm) & 3.4-34.0 & 70 \\ File & \#Gr.nk & ITO.nk \\ Metal work function & 3.0 eV & Yes (flatband) \\ Absorption loss & \#Gr.abs & ITO.abs \\ External reflection constant & \#Gr.ref & aSiCSi\_ITO.ref \\ Surface condition & Textured & Textured \\ Internal reflection constant & 0 & 0 \\ \hline \end{tabular}
\end{table} 
Table 2: Front and back contact parameters. \begin{table}
\begin{tabular}{c c c c c} \hline
**Metallization Parameters** & \multicolumn{2}{c}{**Fingers**} & \multicolumn{2}{c}{**Busbars**} \\ \hline  & Front & Back & Front & Back \\ Number & 120 & 120 & 5 & 5 \\ Height (\(\mathrm{\mu m}\)) & 30 & 30 & 30 & 30 \\ Width (\(\mathrm{\mu m}\)) & 45 & 45 & 500 & 500 \\ Cell area [cm\({}^{2}\)] & & & 244.315 & & \\ \hline \end{tabular}
\end{table} 
Table 3: Front and back metallization parameters. cause this leads to the Fermi energy level \((E_{f})\) being lower than the conduction energy \(E_{c}\) in the \(c-Si\) shell, which is not possible [17]. However, if the carrier concentration is \(>\)0.4 \(\times\) 10\({}^{17}\) 1/cm\({}^{3}\) in the \(c-Si\) layer concentration, this corresponds to \(J_{sc}=34.86\) mA/cm\({}^{2}\). The \(V_{oc}\) curve tends to decay with increasing donor concentration when the light strikes on the back and front parts. Bifaciality comes closer to 1 when reducing the concentration. Additionally, the energy conversion efficiency and the fill factor reach the highest value at a low concentration. For Atacama Desert solar spectral irradiance, when modeling is performed considering the fact that the light strikes the back side of the cell, the current density reaches the highest value, \(J_{sc}=34.86\) mA/cm\({}^{2}\), at a concentration of 10 \(\times\) 10\({}^{16}\) 1/cm\({}^{3}\). The optimum donor concentration is chosen to be the one that maximizes the short current density, which in Figure 5 is marked with a red circle for both spectra because the modeling is performed separately and independently when (i.) the light falls from the front and (ii.) when the light falls from behind. The electrical characteristics of the \(p-type\) hydrogenated amorphous silicon layer are very important for HIT solar cells. Figure 10 shows the \(a-Si:H(p^{+})\) hydrogenated amorphous silicon layer optimization with \(p-type\) carriers varying between \((6.05-6.30)\times 10^{17}\) 1/cm\({}^{3}\). In the modeling, most parameters increase with the number of carriers. However, for large concentrations, the Fermi energy level of the acceptors \((E_{f})\) reaches higher values than the valence energy levels \((E_{v})\), which is physically not possible.