## 3 Results and Discussion
### Path towards Cell Parameters Optimization  
First, we examined the case when varying the thickness of nc-SiO\({}_{\rm x}\). From the results, we learned that TOPCon solar cell performance is affected by the nc-SiO\({}_{\rm x}\) properties, such as the fabrication process and layer thickness, significantly. In this Section 3.3, we present a set of simulation results for the carrier transport in the TOPCon structure as used for the current-voltage measurement. Note that open circuit voltage (V\({}_{\rm oc}\)), as well as short circuit current (J\({}_{\rm sc}\)), is derived from the current-voltage characteristics curve to assess the entire Si solar cell performance, because this indicates the achievement of the solar cell in terms of efficiency. The consequences regarding tunnel oxide thickness were investigated along with their work function, as depicted in Figure 6. J\({}_{\rm sc}\) was greatly improved by embedding a thin oxide layer, which was similar to the case of a nanocrystalline-based TOPCon structure [28]. Generally, V\({}_{\rm oc}\) and J\({}_{\rm sc}\) increased gradually to the maximum value as the work function reduced and the oxide thickness increased. It should be note that the J\({}_{\rm sc}\) would drop down quickly as the tunnel oxide exceeded a certain thickness because of the invalidity of carrier tunneling (not shown in Figure 6); however, the V\({}_{\rm oc}\) and J\({}_{\rm sc}\) showed the same characteristics at the work function range from 3.6 to 4.0 eV. The nc-SiO\({}_{\rm x}\) layer, with a thickness of 30 nm, was interpreted as the model to elucidate this circumstance, for example, when the V\({}_{\rm oc}\) increased from 733 to 760 mV through an increase of the thickness of the oxide ranging from 0.6 to 1.8 nm. Particular crystalline nanostructures with a 4.0 eV work function and a thickness of 30 nm exhibited better performance with the tunnel oxide of a 1.2 nm thickness. The champion performing V\({}_{\rm oc}\) of the nc-SiO\({}_{\rm x}\) TOPCon solar cell reached 760 mV, and the J\({}_{\rm sc}\) reached 43 mA/cm\({}^{2}\) at a 1.2 nm thin tunnel oxide layer with up to a 4.0 eV work function, as shown in Figure 6a,b. The results of the V\({}_{\rm oc}\) and J\({}_{\rm sc}\), at a work function level of 3.6 eV, 3.8 eV, and 4.0 eV, respectively, show almost the same result. which is depicted in Figure 6a,b. This result suggests that this novel advanced TOPCon solar cell through an nc-SiO\({}_{\rm x}\) layer with a superior tunnel oxide, attains magnificent surface passivation, which is competitive with an ordinary poly-Si TOPCon solar cell. [PERSON] et al. [29] reported on a TOPCon solar cell with a low-work function electron-selective-collection (ESC) as having a V\({}_{\rm oc}\) of 735 (mV) and J\({}_{\rm sc}\) of 37 (mA/cm\({}^{2}\)), with an oxide layer over 0.8 nm and a work function range from 3.2 eV to 4.0 eV; however, in our novel TOPCon structure with the nc-SiO\({}_{\rm x}\) layer, the results achieved up to 760 (mV) V\({}_{\rm oc}\) and 43 (mA/cm\({}^{2}\)) J\({}_{\rm sc}\) with an oxide layer of \(\sim\)1.2 nm and work function up to 4.0 eV. Moreover, a few practical problems that might hinder the development of an experimental, high-efficiency TOPCon solar cell are now discussed. The first and most critical issue is determining how to produce a thin, low-D\({}_{\rm ltr}\), and low-D\({}_{\rm ph}\) oxide layer. A wet, chemically grown oxide layer (such as hot HNO\({}_{3}\)) is often of poor quality, with a high density of interfacial defects. To eradicate the defects in these oxides, a high-temperature anneal of 800 \({}^{\circ}\)C to 1100 \({}^{\circ}\)C is necessary; however, the growth of the oxide thickness is a side effect of high-temperature anneals, e.g., only the 800 \({}^{\circ}\)C anneal can lead to an oxide of \(>\)2 nm that will decay the fill factor significantly. Figure 5: Improvements in recombination current density and contact resistance after FGA annealing of the annealed nc-SiO\({}_{\rm x}\) layer.