## 5 Modeling and Simulating Si-SC Structures
### Modeling and Simulation of Si-SC with SLARC  
The optical reflectivity of Si-SC structures with and without SLARCs was experimentally and numerically investigated. SLARCs composed of SiO\({}_{2}\) and Si\({}_{3}\)N\({}_{4}\), each with a thickness of 90 nm, were fabricated and characterized. Figure 5 presents the measured and simulated reflectivity spectra for these structures. A comparative analysis of reflectivity values at specific wavelengths is provided in Table 2. A strong correlation was observed between the experimental and simulated reflectivity data for Si-SC structures with and without SLARCs, validating the accuracy of the modeling approach. Figure 5: The reflectivity spectra of Si-SCs with and without SLARCs: (**a**) measured reflectivity of Si-SC with SiO\({}_{2}\) SLARC (90 nm), and Si-SC with Si\({}_{3}\)N\({}_{4}\) ARC (90 nm), and (**b**) simulated reflectivity of Si-SC with and without SiO\({}_{2}\) and Si\({}_{3}\)N\({}_{4}\) SLARCs (quarter-wave thickness). All measurements and simulations were performed at room temperature over a wavelength range of 350 nm to 1000 nm. The obtained reflectivity data, in conjunction with refractive index measurements, enabled the calculation of optimal SLARC thicknesses based on the quarter-wave principle at a reference wavelength of 550 nm. The resulting SLARC configurations (SiO\({}_{2}\): 101 nm, Si\({}_{3}\)N\({}_{4}\): 73 nm) were then simulated to assess their impact on reflectivity across the solar spectrum (Figure 5b). To evaluate the electrical performance of the optimized SLARC structures, the IQE and EQE of Si-SCs were determined. The device structure was modeled using a top SiO\({}_{2}\) or Si\({}_{3}\)N\({}_{4}\) layer, a silver back reflector, and an aluminum emitter. Surface recombination velocities were assigned as follows: 1000 cm/s for aluminum, 10\({}^{7}\) cm/s for silver, and 1000 cm/s for both electrons and holes at the SiO\({}_{2}\)-Si and Si\({}_{3}\)N\({}_{4}\)-Si interfaces. In the electrical simulation, the electron and hole concentrations in the Si-SC are both set to \(1\times 10^{20}\) cm\({}^{-3}\)[20]. Table 3 presents a comparative analysis of IQE and EQE at selected wavelengths for Si-SCs with and without SLARC of SiO\({}_{2}\) (101 nm) and Si\({}_{3}\)N\({}_{4}\) (73 nm). While IQE provides insights into intrinsic material properties, EQE reflects the overall device efficiency, including optical losses. The observed discrepancies between IQE and EQE at shorter wavelengths highlight the impact of surface recombination on charge carrier collection. The electrical characteristics of Si-SCs, including \(V_{oc}\), \(J_{sc}\), FF, and PCE, were determined using Lumerical CHARGE simulator. The calculated J-V curves (Figure 6) reveal the impact of SLARCs on device performance. The observed enhancement in \(J_{sc}\) for SLARC-coated devices is attributed to the improved light harvesting efficiency, as evidenced by the reduced reflectivity. Table 4 summarizes the key electrical performance parameters for Si-SC structures with and without SLARCs. The inclusion of SiO\({}_{2}\) and Si\({}_{3}\)N\({}_{4}\) SLARCs resulted in significant enhancements in \(J_{sc}\) from 25.18 mA/cm\({}^{2}\) to 37.11 mA/cm\({}^{2}\), correspondingly increasing PCE from 12.27% to 18.47%. While \(V_{oc}\) and FF remained relatively constant, the observed improvements in \(J_{sc}\) and PCE directly correlate with the enhanced light harvesting capabilities of Si-SC with SLARCs, as evidenced by the IQE and EQE data.