## 3 Results and Discussion
### Optimization by Changing the Cell's Layers' Thickness  
The layer thickness \((w)\) plays a very important role in the optimization of the material, but, at the same time, it is extremely important to have an optimized thickness to achieve the highest energy conversion efficiency. This process can be carried out in the laboratory by varying the manufacturing time or the intensity of the gas flow [51; 52]. Figure 12 in the Appendix A shows the optimization of the \(n^{+}\)\((a-Si:H\)\(n^{+})\) hydrogenated amorphous silicon layer for thicknesses varying between \((3-12)\times 10^{-7}\) cm. Here, bifaciality comes closer to 1 at a smaller thickness. The open-circuit voltage and the short-circuit current density are constant in the simulation when the light strikes the front part of the solar cell, but they decrease as the thickness increases when modeling with the light striking from the back part of the solar cell. The fill factor is constant when the light strikes from the front part, but it has a slight decay of thickness when the light strikes from the back part. The electrical properties show constant values when the light strikes from the front part. Thus, the \(n^{+}\) layer thickness does not play an important role in HIT solar cells when the light strikes only from the front part, but if the light strikes from the back side, the \(n^{+}\) layer thickness is quite relevant. We denote the edge of the conduction band by (\(E_{c}\)). Bandshifts (\(\Delta E_{c}\)) are present at each \(a-Si:H(i)/a-Si:H(n)\) interface. If the thickness of the \(n-type\) layer decreases \(\Delta E_{c}=w^{-1/2}\), this calculation is not reflected directly from \(J_{sc}\) in Figure 10. The \(FF\) is shown where the two curves have the same value, and we therefore choose the value of the thickness where it is marked with the red circle. Under AM1.5 standard spectrum, the \(n^{+}\) layer is fixed at 7 nm, while under the Atacama Desert spectrum, it is fixed at 9 nm. Figure 11 in Appendix A shows the optimization of the \(type\)\(p^{+}\)\(a-Si:H(p^{+})\) hydrogenated amorphous silicon layer for thicknesses varying between \((3-12)\times 10^{-7}\)cm, showing that bifaciality is closer to 1 at a larger thickness. The open-circuit voltage values increase with thickness while the fill factor and the energy conversion efficiency decrease as the layer thickness increases. The short-circuit current density decreases as the thickness \((w)\) increases if light strikes from the front part, while it remains constant if the light strikes from the back side. The cell behavior is similar when modeling with AM1.5 standard spectrum or Atacama Desert light intensity. In the \(\mathrm{a-Si(p)/a-Si(i)}\) interface, \(\Delta E_{c}\) has a potential behavior of the form \(\Delta E_{c}=w^{1/2}\). Under the AM1.5 standard spectrum, for \(w=6\) nm, \(\Delta E_{c}\) presents the depletion zone in \(a-Si:H(p)\), which is reflected in the bifacial curve approaching 1 above \(w=6\) nm. The fill factor has the same value regardless of the illuminated size. On the other hand, for \(w=7\) nm, the \(J_{sc}\) and the \(FF\) are reflected under the Atacama Desert spectrum. Figure 11 in Appendix A shows the optimization of the \(n\)\(c-Si(n)\) crystalline silicon wafer with thicknesses varying between \((120-200)\times 10^{-4}\) cm, which shows that bifaciality comes closer to 1 as thickness decreases. The open-circuit voltage tends to decrease as thickness increases. The short-circuit current density values increase as thickness increases when the light strikes from the front part. When modeling with the standard spectrum and light striking from the back part, the short-circuit current density reaches its highest value, i.e., \(160\times 10^{-4}\) cm, so this is the chosen thickness for the \(\mathrm{c-Si}\) wafer under the AM1.5 standard spectrum.