## 3 Results and Discussion
### Path towards Cell Parameters Optimization
The various device parameters were observed for oxide thickness from 0.6 nm to 1.8 nm, and nc-SiO\({}_{\rm x}\) bulk defect density from 1 \(\times\) 10\({}^{17}\) to 1 \(\times\) 10\({}^{21}\) cm\({}^{-3}\), as shown in Figure 8a,b. As demonstrated in Figure 8a, the V\({}_{\rm oc}\) decreased by 0.52 percent from 761 to 757 mV at a 1.2 nm oxide layer due to an increase in the bulk-defect density ranges from 1 \(\times\) 10\({}^{17}\) to 1 \(\times\) 10\({}^{21}\) cm\({}^{3}\). Since the oxide thickness began to increase from 1.2 nm, the V\({}_{\rm oc}\) reached a minimum value of approximately 755 mV at the work function of 4.0 eV for all the oxide layers. The studies revealed that a sufficient oxide thickness might tolerate the negative effects of defects while still producing satisfactory outcomes. The J\({}_{\rm sc}\) impact of the oxide thickness under a bulk-defect density in the nc-SiO\({}_{\rm 2}\) layer is shown in Figure 8b. Cell performance and surface passivation were diminished by the increase in oxide thickness. Luckily, after introducing a proper thin oxide around 1.2 nm, the J\({}_{\rm sc}\) turned less sensitive with the nc-SiO\({}_{\rm 2}\) thickness. In particular, the J\({}_{\rm sc}\) reached the highest value of about 43 mA/cm\({}^{2}\) with regards to an oxide thickness of around 1.2 nm. According to the findings, it was possible to achieve the maximum J\({}_{\rm sc}\) by inserting an appropriate thin tunnel oxide that eliminated the influence of the defects. The values of the tunnel oxide layers' interface trap density (D\({}_{\rm it}\)) were incorporated into the AFORS HET simulation, the results of which are presented in Figure 9. The effects of SiO\({}_{\rm 2}\) quality on the surface passivation and cell performance are investigated using D\({}_{\rm it}\) characteristics. It should be noted that D\({}_{\rm it}\) is fixed within the interface of the Si wafer and the oxide layer. As presented in Figure 9, the V\({}_{\rm oc}\) and J\({}_{\rm sc}\) of the complete structure decreased with the increase of D\({}_{\rm it}\). The D\({}_{\rm it}\) was ranging from 1 \(\times\) 10\({}^{8}\) cm\({}^{-2}\) eV\({}^{-1}\) to 1 \(\times\) 10\({}^{12}\) cm\({}^{-2}\) eV\({}^{-1}\). A more prominent J\({}_{\rm sc}\), V\({}_{\rm oc}\), and overall cell efficiency were achieved with a minimum D\({}_{\rm it}\) value. The main factor which affected the conversion efficiency was the V\({}_{\rm oc}\) (761.5 mV) for the minimal D\({}_{\rm it}\) (1 \(\times\) 10\({}^{8}\) cm\({}^{-2}\) eV\({}^{-1}\)) at a perfect thin oxide layer of around 1.2 nm, as presented in Figure 9a. The rear electrode directly contacted the back-surface field in the passivated emitter and rear cell (PERC) solar cells, whereas the carrier  
Figure 7: Effect of donor concentration (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. on the rear side of the structure passed to the nc-SiO\({}_{\rm x}\) layer through a tunneling mechanism in the passivated contact. Therefore, the tunneling oxide under a minimal D\({}_{\rm it}\) value resulted in an ameliorated conversion efficiency. The highest simulated value J\({}_{\rm sc}\) of 43.5 mA/cm\({}^{2}\) was accomplished when the D\({}_{\rm it}\) had a minimal value of approximately 1 \(\times\) 10\({}^{8}\) cm\({}^{-2}\) eV\({}^{-1}\) at a perfect thin oxide layer of around 1.2 nm, as shown in Figure 9b. The J\({}_{\rm sc}\) kept to above a J\({}_{\rm sc}\) of 43.5 mA/cm\({}^{2}\) at a D\({}_{\rm it}\) value of 1 \(\times\) 10\({}^{8}\) cm\({}^{-2}\) eV\({}^{-1}\), while it decreased to 29 mA/cm\({}^{2}\) when the D\({}_{\rm it}\) rose to 1 \(\times\) 10\({}^{12}\) cm\({}^{-2}\) eV\({}^{-1}\). [PERSON] et al. [30] reported on a TOPCon solar cell having a V\({}_{\rm oc}\) of 712 (mV) and J\({}_{\rm sc}\) of 41.30 (mA/cm\({}^{2}\)) with a D\({}_{\rm it}\) value of 1 \(\times\) 10\({}^{10}\) cm\({}^{-2}\) eV\({}^{-1}\).