## 3 Results and Discussions
### GaAs Single Junction Solar Cell with Variable Pad Thickness  
This study aims to enhance solar cell efficiency by leveraging the similar characteristics of \(AlGaAs\) and the materials used in this design. Consequently, \(AlGaAs\) is incorporated as a buffer layer in the \(GaAs\) single-junction structure, as illustrated in Figure 4. Further, the optimization of this layer is also an essential task to be ensured to achieve greater efficiency.  
Figure 4: Silvaco-Atlas of p+/n+ GaAs single junction with double BSF layer.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**BSF Layer “AlGaInP” (\(\mu\)m)** & \(J_{SC}\) (mA/cm\({}^{2}\)) & \(V_{OC}\) (V) & **FF (\%)** & **\(\eta\) (\%)** \\ \hline One\_BSF = 30 nm & 16.657 & 1.299 & 83.143 & 17.988 \\ One\_BSF = 50 nm & 17.170 & 1.3 & 83.081 & 18.540 \\ Double\_BSF = 30 nm & 18.536 & 1.3 & 83.396 & 20.097 \\ Double\_BSF = 50 nm & 19.384 & 1.3 & 83.660 & 21.088 \\ Other study [36] & 18.33 & 1.440 & 85.60 & 21.59 \\ \hline \end{tabular}
\end{table}
Table 3: Optimized InGaP single-junction solar cell with various thicknesses of the BSF layer.  
In this paper, the thickness of the \(GaAs\) single-junction with double BSF layer structure was optimized in a range from 10 nm to 50 nm, while maintaining a constant doping concentration of 5 \(\times\) 10\({}^{-18}\) cm\({}^{-3}\) in order to study its impact on the cell performance. The dominant parameters related to solar cells, with respect to \(AlGaAs\) layer thickness, are listed in Table 4.  
These parameters show substantial improvements as the thickness of the buffer layer increases, reaching their optimum around 50 nm. The presence of this buffer layer facilitates the efficient transport of photo-generated carriers across the junction, thus leading to a reduction in recombination losses and an accumulation of excess minority carriers at the junction. These combined effects contribute significantly to the overall improvement in the solar cell performance.  
Figure 6 shows that the current density is higher for the solar cell with a layer (50 nm) than for the solar cell with a layer (10 nm). This is due to the fact that the (50 nm) layer is thicker and therefore contains more free electrons. Specifically, the current density for the solar cell with a 50 nm n-layer is about 33.278 mA/cm\({}^{2}\), while the current density for the  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Thickness of AlGaAs Buffer Layer for GaAs SJ (nm)** & \(J_{SC}\) **(mA/cm\({}^{2}\))** & \(V_{OC}\) **(V)** & **FF (\%)** & \(\eta\) **(\%)** \\ \hline
10 nm & 29.821 & 1.036 & 86.901 & 26.850 \\
20 nm & 29.905 & 1.036 & 86.894 & 26.925 \\
30 nm & 30.379 & 1.036 & 86.858 & 27.352 \\
40 nm & 31.401 & 1.037 & 86.777 & 28.270 \\
50 nm & 33.278 & 1.039 & 86.626 & 29.954 \\ Other study [37] & 27.80 & 1.050 & 85.55 & 25.0 \\ \hline \end{tabular}
\end{table}
Table 4: Performance parameter of \(GaAs\) BSF with different thicknesses of the buffer layer.  
Figure 5: I–V Characteristic of \(GaAs\) single junction with different buffer layer thickness.  
solar cell with a 10 nm n-layer is about 29.821 mA/cm\({}^{2}\). This represents an increase in the efficiency of approximately 11.6%.