## 3 Results and Discussion
The sum of the absorption at both two active layers is plotted as a red solid line and the total reflection is plotted as a black solid line. The values of absorption at the active layers and total reflection for the reference planar ITO tandem cell are also represented as red and black dotted lines, respectively. Since the reference planar ITO tandem layer is polarization insensitive, the dotted lines are the same for both figures. These figures show that TE behaves better than TM for both parts of our nanostructured tandem cell. Moreover, the c-Si cell partially absorbs energy at short wavelengths as its surface is directly exposed to light. However, most of this absorption comes from the reduction in the total reflectance of the device. Our calculation of the short-circuit current uses the weighted absorption at the active layer with the AM1.5 solar spectrum. Based on these observations, we do not expect the final performance to degrade due to this absorption at short wavelengths at the c-Si cell. When averaging the TE and TM results, we obtained the performance for the unpolarized solar irradiation. Our design maximizes the short-circuit current of each cell. This optimization also provides a lower total reflectance for the proposed design (black solid line in Figure 3) when compared the reference planar device (black dashed line in Figure 3). This reduced total reflectance appears over the whole spectral range of the device. Figure 3: Absorption and reflection for (**a**) TE and (**b**) TM cases. The gray color region represents the absorption of the perovskite active layer and the light blue color region is for the absorption at the c-Si active layer. The red solid line denotes the total absorption in the active layer for both of them and the black solid line is the total reflection of the nanostructure cell. The red and black dotted lines show the total absorption in perovskite and c-Si active layers and total reflection for the planar solar cell, respectively. Figure 2: Short-circuit current maps in terms of the thickness, \(H\), and width, \(W\) of the perovskite layer, for the c-Si cell (**a**) and the perovskite cell (**b**). The black line represents the value of the short-circuit current obtained for the reference planar cell. Regions I and II contain the configuration delivering a smaller or larger \(J_{SC}\) than the planar tandem cell, respectively. The black star denotes the configuration selected in this contribution, meeting the equal short-circuit current condition in both cells of the tandem configuration. Figure 4 shows the maps for the electric and magnetic field distributions for the TE and TM polarized light, respectively. We have evaluated these fields for two wavelengths, \(\lambda_{s}=600\) nm and \(\lambda_{l}=850\) nm, located at the spectral regions where the perovskite and c-Si cells absorb best, respectively. As expected, for \(\lambda_{s}\), the electric and magnetic fields are stronger at the perovskite cell, leaving almost no power for the c-Si cell to absorb. Additionally, for \(\lambda_{l}\), light is redirected by the grating towards the c-Si cell, generating larger field amplitudes. This trend is maintained for an angle of incidence of 60\({}^{\circ}\). In solar energy applications, solar cells receive sun irradiation from very different angles throughout the day. Therefore, solar cell devices must maintain a high performance under oblique illumination conditions. The dependence of the \(J_{SC}\) value of perovskite and c-Si junctions with respect to the angle of incidence is shown in Figure 5. The values for the planar device is also included for comparison. Both devices behave almost the same through the whole angular range, with a slightly better performance of the nanostructured device at small angles of incidence (between 0\({}^{\circ}\) and 20\({}^{\circ}\) degree) and a little better performance of the planar device at large angles of incidence (from 40\({}^{\circ}\) to 60\({}^{\circ}\) degree).