## 3 Results and Discussion
### Path towards Cell Parameters Optimization
In our novel TOPCon structure with an nc-SiO\({}_{\rm x}\) layer, the simulation results reached up to V\({}_{\rm oc}\) 761.5 mV and J\({}_{\rm sc}\) 43.5 mA/cm\({}^{2}\) with an oxide layer of \(\sim\)1.2 nm plus a D\({}_{\rm it}\) value of 1 \(\times\) 10\({}^{8}\) cm\({}^{-2}\) eV\({}^{-1}\). [PERSON] et al. [31] published an experimentally based result for a low D\({}_{\rm it}\) value of up to 7 \(\times\) 10\({}^{11}\) cm\({}^{-2}\) eV\({}^{-1}\) that considered a tunnel oxide's strong passivation ability. Wet chemical oxidation procedures were used to synthesize this tunnel oxide. Figure 8: Effect of various bulk-defect density (1 \(\times\) 10\({}^{17}\)–1 \(\times\) 10\({}^{21}\) cm\({}^{-3}\)) with various oxide thicknesses (0.6–1.8 nm) on (a) V\({}_{\rm oc}\) and (b) J\({}_{\rm sc}\) on the TOPCon solar cell. Figure 9: Effect of various interface trap densities (1 \(\times\) 10\({}^{8}\)–1 \(\times\) 10\({}^{12}\) cm\({}^{-2}\)/eV) with various oxide thicknesses (0.6–1.8 nm) on (a) V\({}_{\rm oc}\) and (b) J\({}_{\rm sc}\) on the TOPCon solar cell. From the carrier transport study, we learned that in addition to the tunneling, the transport through pinholes affected the J-V characteristics of the junction significantly. Hence, it is convincing to suppose that carrier transport through pinholes could influence the performance of real TOPCon solar cells. The existence of a high-density oxide pinhole was also harmful to surface passivation, as presented in Figure 10. Therefore, the TOPCon solar cell performance, considering the probability of carrier transport through pinholes ranging from 10\({}^{-8}\) to10\({}^{1}\), was studied with five different thicknesses of the SiO\({}_{\text{x}}\) layer ranging from 0.6 nm, 0.9 nm, 1.2 nm, 1.5 nm, and 1.8 nm. Figure 10a,b shows the performance parameters considering the transport through pinholes. In such a case, the thin SiO\({}_{\text{x}}\) layer furnished quite a high tunneling current to permit a majority of the photo-carrier. A lower fill factor (FF) was found without transport via pinholes; a modest amount of transport through the pinholes increased the FF; too much transport through the pinholes decreased the FF, V\({}_{\text{oc}}\), and J\({}_{\text{sc}}\) considerably. Tunneling transport in the TOPCon solar cells with a comparably thick SiO\({}_{\text{x}}\) (1.5 nm and 1.8 nm) could not provide enough transport channels, limiting the current flow, and leading to a high series resistance (R\({}_{\text{s}}\)) as well as an inferior FF. Through the addition of the pinhole mitigated transport at a pinhole density ranging from 10\({}^{-8}\) to10\({}^{-6}\), the FF rose, Rs diminished, and thus, overall efficiency was enhanced. In the region of prominent pinhole transport (>10\({}^{-3}\)), the performance parameters (V\({}_{\text{oc}}\), and J\({}_{\text{sc}}\)) began to decline at all thicknesses of the SiO\({}_{\text{x}}\) layer and resulted in a diminishing efficiency. When pinholes were involved, apart from the transport through tunneling, the carriers were also transported through the pinholes, which diminished the R\({}_{\text{s}}\), and hence, ameliorated the FF as well as the efficiency. Nevertheless, the results showed that raising the pinhole transport adds a shunt path as well as decreases the carrier built up within the junction in a context of an open circuit condition, thus diminishing the V\({}_{\text{oc}}\). Moreover, the excess pinholes could decrease the passivation quality, raise the interface recombination, and deteriorate the cell's performance. With the help of a simulation study, it was shown that an appropriate amount of pinholes in the thin SiO\({}_{2}\) passivation layer is required for prominent efficiency of the TOPCon solar cells through a thick SiO\({}_{2}\), namely, 1.2 nm, which is a necessary for ameliorating the V\({}_{\text{oc}}\) as well as J\({}_{\text{sc}}\) in real solar cells.