## 3 Results and Discussion
### Path towards Cell Parameters Optimization
The V\({}_{\text{oc}}\) and J\({}_{\text{sc}}\) values for SiO\({}_{2}\) thicknesses of 1.2 nm, 1.5 nm, and 1.8 nm, respectively, indicate approximately the same results, and again in the case of SiO\({}_{2}\) thicknesses of 0.6 nm and 0.9 nm, which are illustrated in Figure 10a,b. [PERSON] et al. [32] reported on a TOPCon solar cell with poly-Si having a V\({}_{\text{oc}}\) of 735 (mV) and J\({}_{\text{sc}}\) of 37.7 (mA/cm\({}^{2}\)), with an oxide layer of 1.4 nm and pinhole density of 10\({}^{-6}\)-10\({}^{-5}\); however, in our novel TOPCon structure with an nc-SiO\({}_{\text{x}}\) layer, the results reached up to a V\({}_{\text{oc}}\) of 761 mV and J\({}_{\text{sc}}\) of 42.5 mA/cm\({}^{2}\), with an oxide thickness of -1.2 nm and pinhole density of 1 \(\times\) 10\({}^{-4}\). The tunnel oxide increased the passivation quality at the rear, decreasing the current recombination density [33]. A thicker oxide layer increased the bandgap between electrons and holes at the quasi-fermi levels, thus increasing the V\({}_{\text{oc}}\) and reducing the leak current to almost zero [34]. On increasing the width of the thin oxide layer, the effect of SRV reduced, as observed in Figure 11. With the thinner oxide layer (~0.6 nm thick), there was a substantial decline in V\({}_{\text{oc}}\) from 761.5 to 742 mV with the rear SRV from 1 \(\times\) 10\({}^{1}\) to 1 \(\times\) 10\({}^{9}\) cm/s, thereby the J\({}_{\text{sc}}\) was decreased from 38 to 34 mA/cm\({}^{2}\). From the increase in oxide thickness, the SRV limiting effect was released and, therefore, the V\({}_{\text{oc}}\) as well as the J\({}_{\text{sc}}\) improved. With the thickness above 1.2 nm in Figure 11a, the SRV impact over V\({}_{\text{oc}}\) was diminished. In Figure 11b, the tunneling oxide thickness above 1.2 nm was essential for excellent passivation, where the SRV did not affect the cell performance. The cause of that decline can be understood with the dark J-V characteristics, with a diminishing tunneling current density (15-16 times) with every single increase of 0.2 nm oxide thickness [25], as well as a rise in parasitic resistance. As a result of these impressions, the efficiency of the structure rose to a 1.2 nm thickness, although, it then began to diminish. Through a rise in the oxide thickness, a diminishing tunneling efficiency was observed, and the conversion efficiency should diminish because of a reduced current passage. Meanwhile, the oxide layer decreased recombination because of the best passivation outcome as well as the selective passage of the charge carrier by means of tunneling. The reduction in tunneling efficiency was controlled by a decrease in recombination; consequently, we saw an overall increase in conversion efficiency. To limit the influence of SRV on the solar cell's efficiency, the tunnel oxide layer thickness should be kept between 0.8 and 1.2 nm. [PERSON] et al. [26] reported on a TOPCon solar cell with n+ poly-Si having a V\({}_{\rm{oc}}\) of 761 (mV) and J\({}_{\rm{sc}}\) of 43.2 (mA/cm\({}^{2}\)), with an oxide layer of \(\sim\)1 nm and SRV value of 1 \(\times\) 10\({}^{4}\) cm/s; however, in our novel TOPCon structure with an nc-SiO\({}_{\rm{x}}\) layer, the results reached up to 761.5 (mV) V\({}_{\rm{oc}}\) and 43.5 (mA/cm\({}^{2}\)) J\({}_{\rm{sc}}\), respectively, with an oxide layer of \(\sim\)1.2 nm and an SRV value of 1 \(\times\) 10\({}^{1}\). Figure 5:0 Effect of rear-SRV (1 \(\times\) 10\({}^{1}\)-1 \(\times\) 10\({}^{9}\) cm/s) with various oxide thickness (0.6–1.8 nm) on (**a**) V\({}_{\rm{oc}}\) and (**b**) J\({}_{\rm{sc}}\) on the TOPCon solar cell. Figure 5:1 Effect of pinholes density (1 \(\times\) 10\({}^{-7}\)–1 \(\times\) 10\({}^{1}\)) with various oxide thicknesses (0.6–1.8 nm) on (**a**) V\({}_{\rm{oc}}\) and (**b**) J\({}_{\rm{sc}}\) on the TOPCon solar cell.