## 3 Results and Discussion
### Path towards Cell Parameters Optimization
PECVD is a better tool for depositing a low-D\({}_{\text{tt}}\) oxide. Furthermore, it is challenging to maintain an oxide thickness of less than 2 nm and build a dense oxide layer with a low pinhole density using this approach. Thermal oxidation, which we adopted and detailed before in the experimental phase, has proven to be the most stable and probable contender among the remaining techniques for depositing a thin oxide. Tunneling efficiency decreases as oxide thickness grows, but tunneling efficiency improves as doping concentration increases. Therefore, to obtain high performance and excellent tunneling current in the TOPCon cells, optimization is necessary. Various device parameters were observed for an oxide thickness ranging from 0.6 nm to 1.8 nm and an nc-SiO\({}_{\text{x}}\) doping concentration from 1 \(\times\) 10\({}^{17}\) to 1 \(\times\) 10\({}^{21}\) cm\({}^{-3}\), as shown in Figure 7. Due to surface recombination, the V\({}_{\text{oc}}\) was low with a thick oxide layer and low doping density. As the doping density increased, V\({}_{\text{oc}}\) increased as well as the J\({}_{\text{sc}}\). V\({}_{\text{oc}}\) is a lead parameter to evaluate the device performance because it is computed through a current-voltage curve. Comparatively, similar trends were realized in the V\({}_{\text{oc}}\), as demonstrated in Figure 7a. The V\({}_{\text{oc}}\) was minimized to 745 mV for the architecture with a SiO\({}_{\text{2}}\) layer thickness of 0.6 nm. The maximum V\({}_{\text{oc}}\) value was enhanced up to the 761 mV by contributing a right oxide and nc-SiO\({}_{\text{x}}\) stack layer with proper doping level, which indicated that a TOPCon solar cell has the huge capacity to accomplish a quite high V\({}_{\text{oc}}\), as long as the front-sided surface recombination is depressed. Figure 7b shows that J\({}_{\text{sc}}\) reached up to 43 mA/cm\({}^{\text{2}}\) for the architecture with a SiO\({}_{\text{2}}\) layer of 1.2 nm. J\({}_{\text{sc}}\) was diminished to an inferior value of 25 mA/cm\({}^{\text{2}}\) by using the nc-SiO\({}_{\text{x}}\) layer under a low doping concentration of approximately 1 \(\times\) 10\({}^{17}\) cm\({}^{-3}\). Similarly, the J\({}_{\text{sc}}\) was diminished to about 25 mA/cm\({}^{\text{2}}\) by employing a tunnel oxide layer along with a thickness beyond 1.8 nm. When the thickness of the tunnel oxide was near 1.2 nm, the J\({}_{\text{sc}}\) depicted slight sensitivity to the nc-SiO\({}_{\text{x}}\) doping level, and exclusively once the doping concentration was more prominent with 1 \(\times\) 10\({}^{21}\) cm\({}^{-3}\). This required that the J\({}_{\text{sc}}\) be affected through a number of components, comprising the adopted parameters and mathematics model, such as wafer quality, doping concentration of the wafer, SRV, and doping of the nc-SiO\({}_{\text{x}}\) layer, that can account for the various findings computed by several researchers; however, the physics behind the simulation could not be modified. [PERSON] et al. [25] reported on a TOPCon solar cell with the n\({}^{+}\)-Si layer having a V\({}_{\text{oc}}\) of 737 (mV) and J\({}_{\text{sc}}\) of 37 (mA/cm\({}^{\text{2}}\)), with an oxide layer of \(\sim\)1 nm and a doping level  
Figure 6: Effect of oxide thickness (0.6–1.8 nm) with oxide work function (3.6–4.4 eV) on (**a**) V\({}_{\text{oc}}\) and (**b**) J\({}_{\text{sc}}\) on the TOPCon solar cell. (N\({}_{\rm d}\)) of 1 \(\times\) 10\({}^{19}\) cm\({}^{-3}\). However, in our novel TOPCon structure with an nc-SiO\({}_{\rm x}\) layer, the results reached up to 761 (mV) V\({}_{\rm oc}\) and 43 (mA/cm\({}^{2}\)) J\({}_{\rm sc}\), respectively, with an oxide layer of \(\sim\)1.2 nm and a doping level (N\({}_{\rm d}\)) of 1 \(\times\) 10\({}^{21}\) cm\({}^{-3}\). As the oxide thickness rises, the tunneling efficiency falls, but as the bulk defect density increases, the tunneling efficiency drops.